Internet Draft ETSI TC-SEC (ETSI) S/MIME Working Group J Ross (Security & Standards) expires in six months D Pinkas (Bull) Target Category: Informational N Pope (Security & Standards) March 2000 Electronic Signature Formats for long term electronic signature Status of this Memo This document is an Internet-Draft and is NOT offered in accordance with section of RFC 2026, and the author does not provide the IETF with any rights other than to publish as an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six Months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract The informational RFC defines the format of an electronic signature that can remain valid over long periods. This includes evidence as to its validity even if the signer or verifying party later attempts to deny (repudiates) the validity of the signature. The contents of this Informational RFC is technically equivalent to ETSI ES 201 733 V.1.1.1 Copyright (C). Individual copies of this ETSI deliverable can be downloaded from http://www.etsi.org 1. Introduction This document is intended to cover electronic signatures for various types of transactions, including business transactions (e.g. purchase requisition, contract, and invoice applications) where long term validity of such signatures is important. Electronic signatures can be used for any transaction between an individual and a company, between two companies, between an individual and a governmental body, etc. This document is independent of any environment. It can be applied to any environment e.g. smart cards, GSM SIM cards, special programs for electronic signatures etc. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 1] Internet Draft Electronic Signature Formats An electronic signature produced in accordance with this document provides evidence that can be processed to get confidence that some commitment has been explicitly endorsed under a Signature policy, at a given time, by a signer under an identifier, e.g. a name or a pseudonym, and optionally a role. The European Directive on a community framework for Electronic Signatures defines an electronic signature as: "data in electronic form which is attached to or logically associated with other electronic data and which serves as a method of authentication". An electronic signature as used in the current document is a form of advanced electronic signature as defined in the Directive. The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase, as shown) are to be interpreted as described in [RFC2119]. 2 Overview 2.1 Aim The aim of this document is to define an Electronic Signature (ES) that remains valid over long periods. This includes evidence as to its validity even if the signer or verifying party later attempts to deny (repudiates) the validity of the signature. A signer is the entity that creates an electronic signature. This document specifies use of trusted service providers (e.g. TimeStamping Authorities (TSA)), and the data that needs to be archived (e.g. cross certificates and revocation lists) to meet the requirements of long term electronic signatures. An electronic signature defined by this document can be used for arbitration in case of a dispute between the signer and verifier, which may occur at some later time, even years later. This document uses a signature policy, referenced by the signer, as the basis for establishing the validity of an electronic signature. A Trusted Service Provider (TSP) is an entity that helps to build trust relationships by making available or providing some information upon request. A verifier is an entity that verifies an evidence. (ISO/IEC 13888-1 [13]). Within the context of this document this is an entity that validates an electronic signature. A signature policy is a set of rules for the creation and validation of an electronic signature, under which the signature can be determined to be valid 2.2 Basis of Present Document This document is based on the use of public key cryptography to produce digital signatures, supported by public key certificates. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 2] Internet Draft Electronic Signature Formats A Public key certificate is a public keys of a user, together with some other information, rendered unforgeable by encipherment with the private key of the Certification Authority (CA) which issued it (ITU-T Recommendation X.509 [1]). This document also uses timestamping services to prove the validity of a signature long after the normal lifetime of critical elements of an electronic signature and to support non-repudiation. It also, as an option, uses additional timestamps to provide very long-term protection against key compromise or weakened algorithms. This document builds on existing standards that are widely adopted. This includes: * RFC 2630 [9] Crytographic Message Syntax (CMS); * ITU-T Recommendation X.509 [1] Authentication framework; * RFC 2459 [7] Internet X.509 Public Key Infrastructure (PKIX) Certificate and CRL Profile; * RFC (to be published) PKIX Timestamping protocol. NOTE: See clause 2 for a full set of references. 2.3 Major Parties The following are the major parties involved in a business transaction supported by electronic signatures as defined in this document: * the Signer; * the Verifier; * Trusted Service Providers (TSP); * the Arbitrator. The arbitrator is an entity that may be used to arbitrate a dispute between a signer and verifier when there is a disagreement on the validity of a digital signature. The Signer is the entity that creates the electronic signature. When the signer digitally signs over data using the prescribed format, this represents a commitment on behalf of the signing entity to the data being signed. The Verifier is the entity that validates the electronic signature, it may be a single entity or multiple entities. The Trusted Service Providers (TSPs) are one or more entities that help to build trust relationships between the signer and verifier. They support the signer and verifier by means of supporting services including: user certificates, cross-certificates, timestamping tokens, CRLs, ARLs, OCSP responses. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 3] Internet Draft Electronic Signature Formats The following TSPs are used to support the functions defined in this document: * Certification Authorities; * Registration Authorities; * Repository Authorities (e.g. a Directory); * TimeStamping Authorities; * Signature Policy Issuers. Certification Authorities provide users with public key certificates. Registration Authorities allows the registration of entities before a CA generates certificates. Repository Authorities publish CRLs issued by CAs, signature policies issued by Signature Policy Issuers and optionally public key certificates. TimeStamping Authorities attest that some data was formed before a given trusted time. Signature Policy Issuers define the technical and procedural requirements for electronic signature creation and validation, in order to meet a particular business need. In some cases the following additional TSPs are needed: * Attribute Authorities. Attributes Authorities provide users with attributes linked to public key certificates An Arbitrator is an entity that arbitrates disputes between a signer and a verifier. A signature policy issuer is an entity that defines the technical and procedural requirements for electronic signature creation and validation, in order to meet a particular business need 2.4 Electronic Signatures and Validation Data Validation of an electronic signature in accordance with this document requires: * The electronic signature; this includes: - the signature policy; - the signed user data; - the digital signature; - other signed attributes provided by the signer. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 4] Internet Draft Electronic Signature Formats * Validation data which is the additional data needed to validate the electronic signature; this includes: - certificates; - revocation status information, - trusted time-stamps from Trusted Service Providers (TSPs). * The signature policy specifies the technical requirements on signature creation and validation in order to meet a particular business need. A given legal/contractual context may recognize a particular signature policy as meeting its requirements. For example: a specific signature policy may be recognized by court of law as meeting the requirements of the European Directive for electronic commerce. A signature policy may be written using a formal notation like ASN.1 (see 6.1) or in an informal free text form provided the rules of the policy are clearly identified. However, for a given signature policy there shall be one definitive form which has a unique binary encoded value. Signed user data is the user's data that is signed. The Digital Signature is the digital signature applied over the following attributes provided by the signer: * hash of the user data; * signature Policy Identifier; * other signed attributes The other signed attributes include any additional information which must be signed to conform to the signature policy or this document (e.g. signing time). The Validation Data may be collected by the signer and/or the verifier and must meet the requirements of the signature policy. Additional data includes CA certificates as well as revocation status information in the form of Certificate Revocation Lists (CRLs) or certificate status information provided by an on-line service. Additional data also includes timestamps and other time related data used to provide evidence of the timing of given events. It is required, as a minimum, that either the signer or verifier obtains a timestamp over the signer's signature. A Certificate Revocation List (CRL) is signed list indicating a set of certificates that are no longer considered valid by the certificate issuer [X.509 FPAM]digital signature: data appended to, or a cryptographic transformation of, a data unit that allows a recipient of the data unit to prove the source and integrity of the data unit and protect against forgery, e.g. by the recipient (ISO 7498-2 [12]) ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 5] Internet Draft Electronic Signature Formats 2.5 Forms of Validation Data An electronic signature may exist in many forms including: * the Electronic Signature (ES), which includes the digital signature and other basic information provided by the signer; * the ES with Timestamp (ES-T), which adds a timestamp to the Electronic Signature, to take initial steps towards providing long term validity; * the ES with Complete validation data (ES-C), which adds to the ES-T references to the complete set of data supporting the validity of the electronic signature (i.e. revocation status information). The signer must provide at least the ES form, but in some cases may decide to provide the ES-T form and in the extreme case could provide the ES-C form. If the signer does not provide ES-T, the verifier must create the ES-T on first receipt of an electronic signature. The ES-T provides independent evidence of the existence of the signature at the time it was first verified which should be near the time it was created, and so protects against later repudiation of the existence of the signature. If the signer does not provide ES-C the verifier must create the ES-C when the complete set of revocation and other validation data is available. The ES satisfies the legal requirements for electronic signatures as defined in the European Directive on electronic signatures, see Annex C for further discussion on relationship of this document to the Directive. It provides basic authentication and integrity protection and can be created without accessing on-line (timestamping) services. However, without the addition of a timestamp the electronic signature does not protect against the threat that the signer later denies having created the electronic signature (i.e. does not provide non-repudiation of its existence). The ES-T time-stamp should be created close to the time that ES was created to provide maximum protection against repudiation. At this time ll the data needed to complete the validation may not be available but what information is readily available may be used to carry out some of the initial checks. For example, only part of the revocation information may be available for verification at that point in time. Generally, the ES-C form cannot be created at the same time as the ES, as it is necessary to allow time for any revocation information to be captured. Also, if a certificate is found to be temporarily suspended, it will be necessary to wait until the end of the suspension period. The signer should only create the ES-C in situations where it was prepared to wait for a sufficient length of time after creating the ES form before dispatching the ES-C. This, however, has the advantage that the verifier can be presented with the complete set of data supporting the validity of the ES. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 6] Internet Draft Electronic Signature Formats Support for ES-C by the verifier is mandated (see clause 14 for specific conformance requirements). An Electronic Signature (ES), with the additional validation data forming the ES-T and ES-C is illustrated in Figure 1: +------------------------------------------------------------ES-C-----+ |+--------------------------------------------ES-T-----+ | ||+------Elect.Signature (ES)----------+ +------------+| +-----------+| |||+---------+ +----------+ +---------+| |Timestamp || |Complete || ||||Signature| | Other | | Digital || |over digital|| |certificate|| ||||Policy ID| | Signed | |Signature|| |signature || |and || |||| | |Attributes| | || +------------+| |revocation || |||+---------+ +----------+ +---------+| | |references || ||+------------------------------------+ | +-----------+| |+-----------------------------------------------------+ | +---------------------------------------------------------------------+ Figure 1: Illustration of an ES, ES-T and ES-C 2.6 Extended Forms of Validation Data The complete validation data (ES-C) described above may be extended to form an ES with eXtended validation data (ES-X) to meet following additional requirements. Firstly, when the verifier does not has access to, * the signer's certificate, * all the CA certificates that make up the full certification path, * all the associated revocation status information, as referenced in the ES-C. then the values of these certificates and revocation information may be added to the ES-C. This form of extended validation data is called a X-Long. Secondly, if there is a risk that any CA keys used in the certificate chain may be compromised, then it is necessary to additionally timestamp the validation data by either: * timestamping all the validation data as held with the ES(ES-C), this eXtended validation data is called a Type 1 X-Timestamp; or * timestamping individual reference data as used for complete validation. This form of eXtended validation data is called a Type 2 X-Timestamp. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 7] Internet Draft Electronic Signature Formats NOTE: The advantages/drawbacks for Type 1 and Type 2 X-Timestamp are discussed in this document (see clause 4.4.6.) If all the above conditions occur then a combination of the two formats above may be used. This form of eXtended validation data is called a X-Long-Timestamped. Support for the extended forms of validation data is optional. An Electronic Signature (ES) , with the additional validation data forming the ES-X long is illustrated in Figure 2: +------------------------------------------------------- ES-X Long--+ |+--------------------------------------- EC-C --------+ | ||+---- Elect.Signature (ES)----+ +--------+| +--------+ | |||+-------+-+-------+-+-------+| +---------+|Complete|| |Complete| | ||||Signa- | |Other | |Digital|| |Timestamp||certi- || |certi- | | ||||ture | |Signed | |Signa- || |over ||ficate || |ficate | | ||||Policy | |Attri- | |ture || |digital ||and || |and | | ||||ID | |butes | | || |signature||revoc. || |revoc. | | |||+-------+ +-------+ +-------+| +---------+|refs || |data | | ||+-----------------------------+ +--------+| +--------+ | |+-----------------------------------------------------+ | +-------------------------------------------------------------------+ Figure 2: Illustration of an ES and ES-X long. An Electronic Signature (ES) , with the additional validation data forming the eXtended Validation Data - Type 1 is illustrated in Figure 3: +---------------------------------------------------------- ES-X 1 -+ |+---------------------------------------- EC-C --------+ | || +---- Elect.Signature (ES)----+ +--------+| +-------+ | || |+-------+ +-------+ +-------+| +---------+|Complete|| | | | || ||Signa- | |Other | |Digital|| |Timestamp||certifi-|| | Time- | | || ||ture | |Signed | |Signa- || |over ||cate and|| | stamp | | || ||Policy | |Attri- | |ture || |digital ||revoc. || | over | | || ||ID | |butes | | || |signature||refs || | CES | | || |+-------+ +-------+ +-------+| +---------+| || | | | || +-----------------------------+ +--------+| +-------+ | |+------------------------------------------------------+ | +-------------------------------------------------------------------+ Figure 3: Illustration of ES with ES-X Type 1 ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 8] Internet Draft Electronic Signature Formats An Electronic Signature (ES) , with the additional validation data forming the eXtended Validation Data - Type 2 is illustrated in Figure 4: +-------------------------------------------------------- ES-X 2 ---+ |+--------------------------------------- EC-C --------+ | ||+---- Elect.Signature (ES)----+ +--------+| +--------+ | |||+-------+ +-------+ +-------+| +---------+|Complete|| |Times | | ||||Signa- | |Other | |Digital|| |Timestamp||certs || |Stamp | | ||||ture | |Signed | |Signa- || |over ||and || |over | | ||||Policy | |Attri- | |ture || |digital ||revoc. || |Complete| | ||||ID | |butes | | || |signature||refs || |certs | | |||+-------+ +-------+ +-------+| +---------+| || |and | | ||+-----------------------------+ +--------+| |revoc. | | || | |refs | | |+-----------------------------------------------------+ +--------+ | +-------------------------------------------------------------------+ Figure 4: Illustration of ES with ES-X Type 2 2.7 Archive Validation Data Before the algorithms, keys and other cryptographic data used at the time the ES-C was built become weak and the cryptographic functions become vulnerable, or the certificates supporting previous timestamps expires, the signed data, the ES-C and any additional information (ES-X) should be timestamped. If possible this should use stronger algorithms (or longer key lengths) than in the original timestamp. This additional data and timestamp is called Archive Validation Data (ES-A). The Timestamping process may be repeated every time the protection used to timestamp a previous ES-A become weak. An ES-A may thus bear multiple embedded time stamps. Support for ES-A is optional. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 9] Internet Draft Electronic Signature Formats An example of an Electronic Signature (ES), with the additional validation data for the ES-C and ES-X forming the ES-A is illustrated in Figure 5. +-------------------------------- ES-A --------- ----------+ | +-------------------- ES-A -----------------+ | | | +--------- ES-X -------------- + | | | | |..............................| +-----+ | +-----+ | | | |..............................| |Time | | |Time | | | | |..............................| |Stamp| | |Stamp| | | | | | +-----+ | +-----+ | | | +----------------------------- + | | | +-------------------------------------------+ | +----------------------------------------------------------+ Figure 5: Illustration of ES -A 2.8 Arbitration The ES-C may be used for arbitration should there be a dispute between the signer and verifier, provided that: * the arbitrator knows where to retrieve the signer's certificate (if not already present), all the cross-certificates and the required CRLs and/or OCSPs responses referenced in the ES-C; * none of the issuing key from the certificate chain have ever been compromised; * the cryptography used at the time the ES-C was built has not been broken at the time the arbitration is performed. When the first condition is not met, then the plaintiff must provide an ES-X Long. When it is known by some external means that the second condition is not met, then the plaintiff must provide an ES-X Timestamped. When the two previous conditions are not met, the plaintiff must provide the two above information (i.e. an ES-X Timestamped and Long). When the last condition is not met, the plaintiff must provide an ES- A. It should be noticed that a verifier may need to get two time stamps at two different instants of time: one soon after the generation of the ES and one soon after some grace period allowing any entity from the certification chain to declare a key compromise. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 10] Internet Draft Electronic Signature Formats 2.9 Validation Process The Validation Process validates an electronic signature in accordance with the requirements of the signature policy. The output status of the validation process can be: * valid; * invalid; ... * incomplete verification. A Valid response indicates that the signature has passed verification and it complies with the signature validation policy. A signature validation policy is a part of the signature policy which specifies the technical requirements on the signer in creating a signature and verifier when validating a signature An Invalid response indicates that either the signature format is incorrect or that the digital signature value fails verification (e.g. the integrity checks on the digital signature value fails or any of the certificates on which the digital signature verification depends is known to be invalid or revoked). An Incomplete Validation response indicates that the format and digital signature verifications have not failed but there is insufficient information to determine if the electronic signature is valid under the signature policy. This can include situations where additional information, which does not effect the validity of the digital signature value, may be available but is invalid. In the case of Incomplete Validation, it may be possible to request that the electronic signature be checked again at a later date when additional validation information might become available. Also, in the case of incomplete validation, additional information may be made available to the application or user, thus allowing the application or user to decide what to do with partially correct electronic signatures. The validation process may also output validation data : * a signature timestamp; * the complete validation data; * the archive validation data. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 11] Internet Draft Electronic Signature Formats 2.10 Example Validation Sequence As described earlier the signer or verifier may collect all the additional data that forms the Electronic Signature. Figure 6, and subsequent description, describes how the validation process may build up a complete electronic signature over time. +---------------------------------------- ES-C ----------+ |+----------------------------- ES-T -------+ | ||+--- Elect.Signature (ES) ----+ | +--------+ | |||+-------+ +-------+ +-------+|+---------+| |Complete| | ||||Signa- | |Other | |Digital|||Timestamp|| |certifi-| | ||||ture | |Signed | |Signa- |||over || |cate and| | ||||Policy | |Attri- | |ture |||digital || |revoca- | | ||||ID | |butes | | |||signature|| |tion | | |||+-------+ +-------+ +-------+|+---------+| |referen-| | ||+------------\----------------+ ^ | |ces | | || \ | | +--------+ | || \ 1 / | ^ | |+----------------\----------------/--------+ | | +------------------\--------------/-------------- /------+ \ /2 ----3-----/ +----------+ | / / | Signed |\ v / | |User data | \ +--------------------+ +------------+ +----------+ \--->| Validation Process |---> |- Valid | +---|--^-------|--^--+ 4 |- Invalid | | | | | |- Validation| v | v | | Incomplete| +---------+ +--------+ +------------+ |Signature| |Trusted | | Policy | |Service | | Issuer | |Provider| +---------+ +--------+ Figure 6: Illustration of an ES with Complete validation data (ES-C) Soon after receiving the electronic signature (ES) from the signer (1), the digital signature value may be checked, the validation process must at least add a time-stamp (2), unless the signer has provided one which is trusted by the verifier. The validation process may also validate the electronic signature, as required under the identified signature policy, using additional data (e.g. certificates, CRL, etc.) provided by trusted service providers. If the validation process is not complete then the output from this stage is the ES-T. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 12] Internet Draft Electronic Signature Formats When all the additional data (e.g. the complete certificate and revocation information) necessary to validate the electronic signature first becomes available, then the validation process: * obtains all the necessary additional certificate and revocation status information; * completes all the validation checks on the ES, using the complete certificate and revocation information (if a timestamp is not already present, this may be added at the same stage combining ES-T and ES-C process); * records the complete certificate and revocation references (3); * indicates the validity status to the user (4). At the same time as the validation process creates the ES-C, the validation process may provide and/or record the values of certificates and revocation status information used in ES-C, called the ES-X Long (5). This is illustrated in figure 7: +---------------------------------------------------- ES-X ---------+ |+--------------------------------------- ES-C --------+ +--------+ | ||+--- Elect.Signature (ES) ----+ +--------+ | |Complete| | |||+-------+ +-------+ +-------+|+---------+|Complete| | |certifi-| | ||||Signa- | |Other | |Digital|||Timestamp||certifi-| | |cate | | ||||ture | |Signed | |Signa- |||over ||cate and| | |and | | ||||Policy | |Attri- | |ture |||digital ||revoca- | | |revoca- | | ||||ID | |butes | | |||signature||tion | | |tion | | |||+-------+ +---|---+ +-------+|+---------+|referen-| | |Data | | ||+--------------\--------------+ ^ |ces | | +--------+ | || \ | +--------+ | ^ | || \ 1 2/ ^ | | | |+------------------\--------------/-----------|-------+ / | +--------------------\------------/-----------/-------------/-------+ \ / ---3---/ / +----------+ | / / -----------5-----/ | Signed |\ v | | / |User data | \ +--------------------+ +-----------+ +----------+ \--->| Validation Process |---> | - Valid | +---|--^-------|--^--+ 4 | - Invalid | | | | | +-----------+ v | v | +---------+ +--------+ |Signature| |Trusted | | Policy | |Service | | Issuer | |Provider| +---------+ +--------+ Figure 7: Illustration ES with eXtended validation data (Long) ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 13] Internet Draft Electronic Signature Formats When the validation process creates the ES-C it may also create extended forms of validation data. A first alternative is to timestamp all data forming the Type 1 X-Timestamp (6). This is illustrated in figure 8: +---------------------------------------------------- ES-X -------+ |+--------------------------------------- ES-C --------+ +------+ | ||+--- Elect.Signature (ES) ----+ +--------+ | |Time- | | |||+-------+ +-------+ +-------+|+---------+|Complete| | |stamp | | ||||Signa- | |Other | |Digital|||Timestamp||certifi-| | |over | | ||||ture | |Signed | |Signa- |||over ||cate and| | |CES | | ||||Policy | |Attri- | |ture |||digital ||revoca- | | +------+ | ||||ID | |butes | | |||signature||tion | | ^ | |||+-------+ +--|----+ +-------+|+---------+|referen-| | | | ||+-------------|---------------+ ^ |ces | | | | || | | +--------+ | | | || \ 1 2/ ^ | | | |+----------------\------------------/---------|-------+ | | +------------------\----------------/----------/-------------/----+ \ / ----3--/ / +----------+ | / / --------------6---/ | Signed |\ v | | / |User data | \ +--------------------+ +-----------+ +----------+ \--->| Validation Process |---> | - Valid | +---|--^-------|--^--+ 4 | - Invalid | | | | | +-----------+ v | v | +---------+ +--------+ |Signature| |Trusted | | Policy | |Service | | Issuer | |Provider| +---------+ +--------+ Figure 8: Illustration of ES with eXtended validation data - Type 1 X- Timestamp ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 14] Internet Draft Electronic Signature Formats Another alternative is to timestamp the certificate and revocation information references used to validate the electronic signature (but not the signature) (6'); this is called Type 2 X-Timestamped. This is illustrated in figure 9: +---------------------------------------------------- ES-X ----------+ |+--------------------------------------- ES-C --------+ +---------+ | ||+--- Elect.Signature (ES) ----+ +--------+ | |Timestamp| | |||+-------+ +-------+ +-------+|+---------+|Complete| | |over | | ||||Signa- | |Other | |Digital|||Timestamp||certifi-| | |Complete | | ||||ture | |Signed | |Signa- |||over ||cate and| | |Certifi- | | ||||Policy | |Attri- | |ture |||digital ||revoc. | | |cate and | | ||||ID | |butes | | |||signature||refs | | |revoc. | | |||+-------+ +---^---+ +-------+|+----^----++---^----+ | |refs | | ||+--------------\--------------+ | | | +---------+ | |+----------------\------------------/----------|------+ ^ | +----------------1-\----------------/----------/--------------|------+ \ / -----3--/ | +----------+ | 2/ / --------------6'-----/ | Signed |\ v | | / |User data | \ +--------------------+ +-----------+ +----------+ \--->| Validation Process |---> | - Valid | +---|--^-------|--^--+ 4 | - Invalid | | | | | +-----------+ v | v | +---------+ +--------+ |Signature| |Trusted | | Policy | |Service | | Issuer | |Provider| +---------+ +--------+ Figure 9: Illustration of ES with eXtended validation data - Type 2 X- Timestamp ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 15] Internet Draft Electronic Signature Formats Before the algorithms used in any of electronic signatures become or are likely, to be compromised or rendered vulnerable in the future, it is necessary to timestamp the entire electronic signature, including all the values of the validation and user data as an ES with Archive validation data (ES-A) An ES-A is illustrated in figure 10: -------------------------------------------- ES-A --------------------+ ----------------------------------------------------------------+ | +------------------------------- EC-C --------++-----+ | | | ||Time-| | | |+-- Elect.Signature (ES) -+ +--------+||stamp| +-------+ | ||+------++-------++-------|+------+|Complete|||over | Complete| | |||Signa-||Other ||Digital||Time- ||certifi-|||CES | |certi- |+----| |||ture ||Signed ||Signa- ||stamp ||cate and||+-----+ |ficate |Arch-| |||Policy||Attri- ||ture ||over ||revoca- ||+------+ |and |ive | |||ID ||butes || ||digit.||tion |||Time- | |revoca-|Time | ||+------++---|---++-------||signa-||referen-|||stamp-| |tion |stamp| |+------------|------------+|ture ||ces |||over | |data |+----| | | +------++--------+|Complete\+-------+ ^ | | | ^ ^ ||cert. | | | | +-------------|----------------|---------|----+|and rev| | | | \ | / |refs. | | | | \ | / +-------+ | | | -----------------\-------------|-------/------------------------+ | | +----------+ \ | / / | | Signed | \2 |3 / /--------------7-------/ | |User data | \ | | / | +-------\--+ \ | | / | ---------\------------|--------|----|---/-----------------------------+ \ v | | | 1\ +--------------------+ +-----------+ \------>| Validation Process |---> | - Valid | +---|--^-------|--^--+ 4 | - Invalid | | | | | +-----------+ v | v | +---------+ +--------+ |Signature| |Trusted | | Policy | |Service | | Issuer | |Provider| +---------+ +--------+ Figure 10: Illustration of an ES with Archive validation data (ES-A) 2.11 Additional optional features This document also defines additional optional features to: * indicate a commitment type being made by the signer; * indicate the role under which a signature was created; * support multiple signatures. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 16] Internet Draft Electronic Signature Formats 3. Data structure of an Electronic Signature This clause uses and builds upon the Crypographic Message Syntax (CMS), as defined in RFC 2630, REF [CMS] , and Enhanced Security Services (ESS), as defined in RFC 2634 [10], REF [ESS] . The overall structure of Electronic Signature is as defined in [CMS]. The Electronic Signature (ES) uses attributes defined in [CMS], [ESS] and this document. This document defines in full the ES attributes which it uses and are not defined elsewhere. The mandated set of attributes and the digital signature value is defined as the minimum Electronic Signature (ES) required by this document. A signature policy MAY mandate other signed attributes are present. 3.1 General Syntax The general syntax of the ES is as defined in [CMS]. 3.2 Data Content Type The data content type of the ES is as defined in [CMS]. 3.3 Signed-data Content Type The Signed-data content type of the ES is as defined in [CMS]. To make sure that the verifier uses the right signers key, this document mandates that the hash of the signers certificate is always included in the Signing Certificate signed attribute. 3.4 SignedData Type The syntax of the SignedData type of the ES is as defined in [CMS]. The fields of type SignedData have the meanings defined [CMS] except that: * version is the syntax version number. The value of version must be 3. * The identification of signer's certificate used to create the signature is always signed. The validation policy may specify requirements for the presence of certain certificates. * The degenerate case where there are no signers is not valid in this document. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 17] Internet Draft Electronic Signature Formats 3.5 EncapsulatedContentInfo Type The syntax of the EncapsulatedContentInfo a type of the ES is as defined in [CMS]. For the purpose of long term validation as defined by this document, it is advisable that either the eContent is present, or the data which is signed is archived in such as way as to preserve the any data encoding. It is important that the OCTET STRING used to generate the signature remains the same every time either the verifier or an arbitrator validates the signature. The degenerate case where there are no signers is not valid in this document. 3.6 SignerInfo Type The syntax of the SignerInfo a type of the ES is as defined in [CMS]. Per-signer information is represented in the type SignerInfo. In the case of multiple independent signatures, there is an instance of this field for each signer. The fields of type SignerInfo have the meanings defined in [CMS} except that: signedAttributes must, as a minimum, contain the following attributes: * ContentType as defined in clause 3.7.1. * MessageDigest as defined in clause 3.7.2. * SigningTime as defined in clause 3.7.3. * SigningCertificate as defined in clause 3.8.1. * SignaturePolicyId as defined in clause 3.9.1. 3.6.1 Message Digest Calculation Process The message digest calculation process is as defined in [CMS]. 3.6.2 Message Signature Generation Process The input to the digital signature generation process is as defined in [CMS]. 3.6.3 Message Signature Verification Process The procedures for CMS signed data validation are as defined in [CMS] and enhanced in this document. The input to the signature verification process includes the signer's public key verified as correct using the ESS Signing Certificate or Other Signing Certificate attribute. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 18] Internet Draft Electronic Signature Formats 3.7 CMS Imported Mandatory Present Attributes The following attributes MUST be present with the signed-data defined by this document. The attributes are defined in [CMS]. 3.7.1 Content Type The syntax of the content-type attribute type of the ES is as defined in [CMS]. 3.7.2 Message Digest The syntax of the message-digest attribute type of the ES is as defined in [CMS]. 3.7.3 Signing Time The syntax of the message-digest attribute type of the ES is as defined in [CMS]and further qualified by this document. The signing-time attribute type specifies the time at which the signer claims to have performed the signing process. This present document recommends the use of GeneralizedTime. 3.8 Alternative Signing Certificate Attributes One, and only one, of the following two alternative attributes MUST be present with the signed-data defined by this document to identify the signing certificate. Both attributes include an identifier and a hash of the signing certificate. The first, which is adopted in existing standards, may be used if with the SHA-1 hashing algorithm. The other hall be used for other hashing algorithms are to be supported. The signing certificate attribute is designed to prevent the simple substitution and re-issue attacks, and to allow for a restricted set of authorization certificates to be used in verifying a signature. 3.8.1 ESS Signing Certificate Attribute Definition The syntax of the signing certificate attribute type of the ES is as defined in [ESS], and further qualified and profile in this document. The ESS signing certificate attribute must be a signed attribute. This document mandates the presence of this attribute as a signed CMS attribute, and the sequence must not be empty. The certificate used to verify the signature must be identified in the sequence, the Signature Validation Policy may mandate other certificates be present, that may include all the certificates up to the point of trust. The encoding of the ESSCertID for this certificate must include the issuerSerial field. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 19] Internet Draft Electronic Signature Formats The issuerAndSerialNumber present in the SignerInfo must be consistent with issuerSerial field. The certificate identified must be used during the signature verification process. If the hash of the certificate does not match the certificate used to verify the signature, the signature must be considered invalid. The sequence of policy information field is not used in this document. NOTE: Where an attribute certificate is used by the signer to associate a role, or other attributes of the signer, with the electronic signature this is placed in the Signer Attribute attribute as defined in clause 3.12.3. 3.8.2 Other Signing Certificate Attribute Definition The following attribute is identical to the ESS SigningCertificate defined above except that this attribute can be used with hashing algorithms other than SHA-1. This attribute must be used in the same manner as defined above for the ESS SigningCertificate attribute. The following object identifier identifies the signing certificate attribute: id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-aa(2) 19 } The signing certificate attribute value has the ASN.1 syntax OtherSigningCertificate OtherSigningCertificate ::= SEQUENCE { certs SEQUENCE OF OtherCertID, policies SEQUENCE OF PolicyInformation OPTIONAL -- NOT USED IN THIS DOCUMENT } OtherCertID ::= SEQUENCE { otherCertHash OtherHash, issuerSerial IssuerSerial OPTIONAL } OtherHash ::= CHOICE { sha1Hash OtherHashValue, -- This contains a SHA-1 hash otherHash OtherHashAlgAndValue} OtherHashValue ::= OCTET STRING OtherHashAlgAndValue ::= SEQUENCE { hashAlgorithm AlgorithmIdentifier, hashValue OtherHashValue } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 20] Internet Draft Electronic Signature Formats 3.9 Additional Mandatory Attributes 3.9.1 Signature policy Identifier This document mandates that a reference to the signature policy, which defines the rules for creation and validation of an electronic signature, is included as a signed attribute with every signature. The signature policy identifier must be a signed attribute. The following object identifier identifies the signature policy identifier attribute: id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-aa(2) 15 } Signature-policy-identifier attribute values have ASN.1 type SignaturePolicyIdentifier. SignaturePolicyIdentifier ::= SEQUENCE { sigPolicyIdentifier SigPolicyId, sigPolicyHash SigPolicyHash, sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF SigPolicyQualifierInfo OPTIONAL} The sigPolicyIdentifier field contains an object-identifier which uniquely identifies a specific version of the signature policy. The syntax of this field is as follows: SigPolicyId ::= OBJECT IDENTIFIER The sigPolicyHash field contains the identifier of the hash algorithm and the hash of the value of the signature policy. If the signature policy is defined using ASN.1 (see 6.1) the hash is calculated on the value without the outer type and length fields and the hashing algorithm must be as specified in the field signPolicyHshAlg. If the signature policy is defined using another structure, the type of structure and the hashing algorithm must be either specified as part of the signature policy, or indicated using a signature policy qualifier. SigPolicyHash ::= ETSIHashAlgAndValue ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 21] Internet Draft Electronic Signature Formats A signature policy identifier may be qualified with other information about the qualifier. The semantics and syntax of the qualifier is as associated with the object-identifier in the sigPolicyQualifierId field. The general syntax of this qualifier is as follows: SigPolicyQualifierInfo ::= SEQUENCE { sigPolicyQualifierId SigPolicyQualifierId, sigQualifier ANY DEFINED BY sigPolicyQualifierId } This document specifies the following qualifiers: * spuri: This contains the web URI or URL reference to the signature policy * spUserNotice: This contains a user notice which should be displayed whenever the signature is validated. -- sigpolicyQualifierIds defined in this document SigPolicyQualifierId ::= OBJECT IDENTIFIER id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-spq(5) 1 } SPuri ::= IA5String id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-spq(5) 2 } SPUserNotice ::= SEQUENCE { noticeRef NoticeReference OPTIONAL, explicitText DisplayText OPTIONAL} NoticeReference ::= SEQUENCE { organization DisplayText, noticeNumbers SEQUENCE OF INTEGER } DisplayText ::= CHOICE { visibleString VisibleString (SIZE (1..200)), bmpString BMPString (SIZE (1..200)), utf8String UTF8String (SIZE (1..200)) } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 22] Internet Draft Electronic Signature Formats 3.10 CMS Imported Optional Attributes The following attributes MAY be present with the signed-data defined by this document. The attributes are defined in ref [CMS] and are imported into this specification and were appropriate qualified and profiling by this document. 3.10.1 Countersignature The syntax of the countersignature attribute type of the ES is as defined in [CMS]. The countersignature attribute must be an unsigned attribute 3.11 ESS Imported Optional Attributes The following attributes MAY be present with the signed-data defined by this document. The attributes are defined in ref [ESS] and are imported into this specification and were appropriate qualified and profiling by this document. 3.11.1 Signed Content Reference Attribute The content reference attribute is a link from one SignedData to another. It may be used to link a reply to the original message to which it refers, or to incorporate by reference one SignedData into another. The content reference attribute MUST be used as defined in [ESS]. The content reference MUST be a signed attribute. The syntax of the content reference attribute type of the ES is as defined in [ESS]. 3.11.2 Content Identifier Attribute The content identifier attribute provides an identifier for the signed content for use when reference may be later required to that content, for example in the content reference attribute in other signed data sent later. The content identifier must be a signed attribute. The syntax of the content identifier attribute type of the ES is as defined in [ESS]. The minimal signedContentIdentifier should contain a concatenation of user-specific identification information (such as a user name or public keying material identification information), a GeneralizedTime string, and a random number. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 23] Internet Draft Electronic Signature Formats 3.12 Additional Optional Attributes 3.12.1 Commitment Type Indication Attribute There may be situation were a signer wants to explicitly indicate to a verifier that by signing the data, it illustrates a type of commitment on behalf of the signer. The commitmentTypeIndication attribute conveys such information. The commitmentTypeIndication attribute must be a signed attribute The commitment type may be: * defined as part of the signature policy, in which case the commitment type has precise semantics that is defined as part of the signature policy. * be a registered type, in which case the commitment type has precise semantics defined by registration, under the rules of the registration authority. Such a registration authority may be a trading association or a legislative authority. The signature policy specifies a set of attributes that it "recognizes". This "recognized" set includes all those commitment types defined as part of the signature policy as well as any externally defined commitment types that the policy may choose to recognize. Only recognized commitment types are allowed in this field. The following object identifier identifies the commitment type indication attribute: id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16} Commitment-Type-Indication attribute values have ASN.1 type CommitmentTypeIndication. CommitmentTypeIndication ::= SEQUENCE { commitmentTypeId CommitmentTypeIdentifier, commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF CommitmentTypeQualifier OPTIONAL} CommitmentTypeIdentifier ::= OBJECT IDENTIFIER CommitmentTypeQualifier ::= SEQUENCE { commitmentTypeIdentifier CommitmentTypeIdentifier, qualifier ANY DEFINED BY commitmentTypeIdentifier } The use of any qualifiers to the commitment type is outside the scope of this document. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 24] Internet Draft Electronic Signature Formats The following generic commitment types are defined in this document: id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1} id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2} id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 3} id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4} id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 5} id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 6} These generic commitment types have the following meaning: Proof of origin indicates that the signer recognizes to have created, approved and sent the message. Proof of receipt indicates that signer recognizes to have received the content of the message. Proof of delivery indicates that the TSP providing that indication has delivered a message in a local store accessible to the recipient of the message. Proof of sender indicates that the entity providing that indication has sent the message (but not necessarily created it). Proof of approval indicates that the signer has approved the content of the message. Proof of creation indicates that the signer has created the message (but not necessarily approved, nor sent it). NOTE: See clause A.3 for a full description of the commitment types defined above. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 25] Internet Draft Electronic Signature Formats 3.12.2 Signer Location The signer-location attribute is an attribute which specifies a mnemonic for an address associated with the signer at a particular geographical (e.g. city) location. The mnemonic is registered in the country in which the signer is located and is used in the provision of the Public Telegram Service (according to ITU-T Recommendation F.1 [5?????]). The signer-location attribute must be a signed attribute. The following object identifier identifies the signer-location attribute: id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17} Signer-location attribute values have ASN.1 type SignerLocation: SignerLocation ::= SEQUENCE { -- at least one of the following must be present countryName [0] DirectoryString OPTIONAL, -- As used to name a Country in X.500 localityName [1] DirectoryString OPTIONAL, -- As used to name a locality in X.500 postalAdddress [2] PostalAddress OPTIONAL } PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString 3.12.3 Signer Attributes The signer-attributes attribute is an attribute which specifies additional attributes of the signer (e.g. role). It may be either: * claimed attributes of the signer; * certified attributes of the signer; * the signer-attribute attribute must be a signed attribute attributes. The signer-attributes attribute must be a signed attribute. The following object identifier identifies the signer-attribute attribute: id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18} signer-attribute attribute values have ASN.1 type SignerAttribute. SignerAttribute ::= SEQUENCE OF CHOICE { claimedAttributes [0] ClaimedAttributes, certifiedAttributes [1] CertifiedAttributes } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 26] Internet Draft Electronic Signature Formats ClaimedAttributes ::= SEQUENCE OF Attribute CertifiedAttributes ::= AttributeCertificate -- As defined in X.509 : see section 10.3 NOTE: The claimed and certified attribute are imported from ITU-T Recommendations X.501 [16] and ITU-T Recommendation X.509 : Draft Amendment on Certificate Extensions, October 1999. 3.12.3 Content Timestamp The content timestamp attribute is an attribute which is the timestamp of the signed data content before it is signed. The content timestamp attribute must be a signed attribute. The following object identifier identifies the signer-attribute attribute: id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 20} Content timestamp attribute values have ASN.1 type ContentTimestamp: ContentTimestamp::= TimeStampToken The value of messageImprint field within TimeStampToken must be a hash of the value of eContent field within encapContentInfo within the signedData. For further information and definition of TimeStampToken see ref .. temp note; need to add the reference to the timestamping RFC. 3.13 Support for Multiple Signatures 3.13.1 Independent Signatures Multiple independent signatures (see clause 55) are supported by independent SignerInfo from each signer. Each SignerInfo must include all the attributes required under this document and must be processed independently by the verifier. 3.13.2 Embedded Signatures Multiple embedded signatures (see clause B.6) are supported using the counter-signature unsigned attribute (see clause 10.1). Each counter signature is carried in Countersignature held as an unsigned attribute to the SignerInfo to which the counter-signature is applied. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 27] Internet Draft Electronic Signature Formats 4. Validation Data This clause specifies the validation data structures which builds on the electronic signature specified in clause 3. This includes: * Timestamp applied to the electronic signature value. * Complete validation data which comprises the timestamp of the signature value, plus references to all the certificates and revocation information used for full validation of the electronic signature. The following optional eXtended forms of validation data are also defined: * X-timestamp: There are two types of timestamp used in extended validation data defined by this document. - Type 1 -Timestamp which comprises a timestamp over the ES with Complete validation data (ES-C). - Type 2 X-Timestamp which comprises of a timestamp over the certification path references and the revocation information references used to support the ES-C. * X-Long : This comprises a Complete validation data plus the actual values of all the certificates and revocation information used in the ES-C. * X-Long-Timestamp: This comprises a Type 1 or Type 2 X-Timestamp plus the actual values of all the certificates and revocation information used in the ES-C. This clause also specifies the data structures used in Archive validation data: * Archive validation data comprises a Complete validation data, the certificate and revocation values (as in a X-Long validation data), any other existing X-timestamps, plus the Signed User data and an additional archive timestamp over all that data. An archive timestamp may be repeatedly applied after long periods to maintain validity when electronic signature and timestamping algorithms weaken. The additional data required to create the forms of electronic signature identified above is carried as unsigned attributes associated with an individual signature by being placed in the unsignedAttrs field of SignerInfo (see clause 6????). Thus all the attributes defined in clause 9?? are unsigned attributes. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 28] Internet Draft Electronic Signature Formats NOTE: Where multiple signatures are to be supported, as described in clause 3.13, each signature has a separate SignerInfo. Thus, each signature requires its own unsigned attribute values to create ES-T, ES-C etc. 4.1 Electronic Signature Timestamp An Electronic Signature with Timestamp is an Electronic Signature for which part, but not all, of the additional data required for validation is available (i.e. some certificates and revocation information is available but not all). The minimum structure Timestamp validation data is: * The Signature Timestamp Attribute as defined in clause 4.1.1 over the ES signature value. 4.1.1 Signature Timestamp Attribute Definition The Signature Timestamp attribute is timestamp of the signature value. It is an unsigned attribute. Several instances of this attribute may occur with an electronic signature, from different TSAs. The Signature Validation Policy specifies, in the signatureTimestampDelay field of TimestampTrustConditions, an maximum acceptable time difference which is allowed between the time indicated in the signing time attribute and the time indicated by the Signature Timestamp attribute. If this delay is exceeded then the electronic signature must be considered as invalid. The following object identifier identifies the Signature Timestamp attribute: id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 14} The Signature timestamp attribute value has ASN.1 type SignatureTimeStampToken: SignatureTimeStampToken ::= TimeStampToken The value of messageImprint field within TimeStampToken must be a hash of the value of signature field within SignerInfo for the signedData being timestamped. For further information and definition of TimeStampToken see [TSP] Temp note ;ref to timestamping doc required ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 29] Internet Draft Electronic Signature Formats 4.2 Complete Validation Data An electronic signature with complete validation data is an Electronic Signature for which all the additional data required for validation (i.e. all certificates and revocation information) is available. Complete validation data (ES-C) build on the electronic signature Timestamp as defined above. The minimum structure of a Complete validation data is: * the Signature Timestamp Attribute, as defined in clause 4.1.1; * Complete Certificate Refs, as defined in clause 4.2.1; * Complete Revocation Refs, as defined in clause 4.2.2. The Complete validation data MAY also include the following additional information, forming a X-Long validation data, for use if later validation processes may not have access to this information: * Complete Certificate Values, as defined in clause 4.2.3; * Complete Revocation Values, as defined in clause 4.2.4. The Complete validation data MAY also include one of the following additional attributes, forming a X-Timestamp validation data, to provide additional protection against later CA compromise and provide integrity of the validation data used: * ES-C Timestamp, as defined in clause 4.2.5; or * Time-Stamped Certificates and CRLs references, as defined in clause 4.2.6. NOTE 1: As long as the CA's are trusted such that these keys cannot be compromised or the cryptography used broken, the ES-C provides long term proof of a valid electronic signature. A valid electronic signature is an electronic signature which passes validation according to a signature validation policy. NOTE 2: The ES-C provides the following important property for long standing signatures; that is having been found once to be valid, must continue to be so months or years later. Long after the validity period of the certificates have expired, or after the user key has been compromised. 4.2.1 Complete Certificate Refs Attribute Definition The Complete Certificate Refs attribute is an unsigned attribute. It references the full set of CA certificates that have been used to validate a ES with Complete validation data (ES-C) up to (but not including) the signer's certificate. Only a single instance of this attribute must occur with an electronic signature. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 31] Internet Draft Electronic Signature Formats Note: The signer's certified is referenced in the signing certificate attribute (see clause 3.1). id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21} The complete certificate refs attribute value has the ASN.1 syntax CompleteCertificateRefs. CompleteCertificateRefs ::= SEQUENCE OF ETSICertID ETSICertID is defined in clause 3.8.2. The IssuerSerial that must be present in ETSICertID. The certHash must match the hash of the certificate referenced. NOTE: Copies of the certificate values may be held using the Certificate Values attribute defined in clause 4.3.1. 4.2.2 Complete Revocation Refs Attribute Definition The Complete Revocation Refs attribute is an unsigned attribute. Only a single instance of this attribute must occur with an electronic signature. It references the full set of the CRL or OCSP responses that have been used in the validation of the signer and CA certificates used in ES with Complete validation data. The following object identifier identifies the CompleteRevocationRefs attribute: id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22} The complete revocation refs attribute value has the ASN.1 syntax CompleteRevocationRefs CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef CrlOcspRef ::= SEQUENCE { crlids [0] CRLListID OPTIONAL, ocspids [1] OcspListID OPTIONAL, otherRev [2] OtherRevRefs OPTIONAL } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 32] Internet Draft Electronic Signature Formats CompleteRevocationRefs must contain one CrlOcspRef for the signing certificate, followed by one for each ETSICertID in the CompleteCertificateRefs attribute. the second and subsequent CrlOcspRef fields must be in the same order as the ETSICertID to which they relate. At least one of CRLListID or OcspListID or OtherRevRefs should be present for all but the "trusted" CA of the certificate path. CRLListID ::= SEQUENCE { crls SEQUENCE OF CrlValidatedID} CrlValidatedID ::= SEQUENCE { crlHash ETSIHash, crlIdentifier CrlIdentifier OPTIONAL} CrlIdentifier ::= SEQUENCE { crlissuer Name, crlIssuedTime UTCTime, crlNumber INTEGER OPTIONAL } OcspListID ::= SEQUENCE { ocspResponses SEQUENCE OF OcspResponsesID} OcspResponsesID ::= SEQUENCE { ocspIdentifier OcspIdentifier, ocspRepHash ETSIHash OPTIONAL } OcspIdentifier ::= SEQUENCE { ocspResponderID ResponderID, -- As in OCSP response data producedAt GeneralizedTime -- As in OCSP response data } When creating an crlValidatedID, the crlHash is computed over the entire DER encoded CRL including the signature. The crlIdentifier would normally be present unless the CRL can be inferred from other information. The crlIdentifier is to identify the CRL using the issuer name and the CRL issued time which must correspond to the time "thisUpdate" contained in the issued CRL. The crlListID attribute is an unsigned attribute. In the case that the identified CRL is a Delta CRL then references to the set of CRLs to provide a complete revocation list must be included. The OcspIdentifier is to identify the OSCP response using the issuer name and the time of issue of the OCSP response which must correspond to the time "producedAt" contained in the issued OCSP response. Since it may be needed to make the difference between two OCSP responses received within the same second, then the hash of the response contained in the OcspResponsesID may be needed to solve the ambiguity. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 33] Internet Draft Electronic Signature Formats NOTE: Copies of the CRL and OCSP responses values may be held using the Revocation Values attribute defined in clause 4.3.2. OtherRevRefs ::= SEQUENCE { otherRevRefType OtherRevRefType, otherRevRefs ANY DEFINED BY otherRevRefType } OtherRevRefType ::= OBJECT IDENTIFIER The syntax and semantics of other revocation references is outside the scope of this document. The definition of the syntax of the other form of revocation information is as identified by OtherRevRefType. 4.3 Extended Validation Data 4.3.1 Certificate Values Attribute Definition The Certificate Values attribute is an unsigned attribute. Only a single instance of this attribute must occur with an electronic signature. It holds the values of certificates referenced in the CompleteCertificateRefs attribute. Note: If an Attribute Certificate is used, it is not provided in this structure but must be provided by the signer as a signer-attributes attribute (see clause 12.3). The following object identifier identifies the CertificateValues attribute: id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23} The certificate values attribute value has the ASN.1 syntax CertificateValues CertificateValues ::= SEQUENCE OF Certificate Certificate is defined in clause 10.1 (which is as defined in ITU-T Recommendation X.509 [1]) ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 34] Internet Draft Electronic Signature Formats 4.3.2 Revocation Values Attribute Definition The Revocation Values attribute is an unsigned attribute. Only a single instance of this attribute must occur with an electronic signature. It holds the values of CRLs and OCSP referenced in the CompleteRevocationRefs attribute. The following object identifier identifies the CertificateValues attribute: id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 24} The revocation values attribute value has the ASN.1 syntax RevocationValues RevocationValues ::= SEQUENCE { crlVals [0] SEQUENCE OF CertificateList OPTIONAL, ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL, otherRevVals [2] OtherRevVals } OtherRevVals ::= SEQUENCE { otherRevValType OtherRevValType, otherRevVals ANY DEFINED BY otherRevValType } OtherRevValType ::= OBJECT IDENTIFIER The syntax and semantics of the other revocation values is outside the scope of this document. The definition of the syntax of the other form of revocation information is as identified by OtherRevRefType. CertificateList is defined in clause 10.2 (which as defined in ITU-T Recommendation X.509 [1]). BasicOCSPResponse is defined in clause 10.3 (which as defined in ??? RFC 2560 [8] ???). 4.3.3 ES-C Timestamp Attribute Definition This attribute is used for the Type 1 X-Timestamped validation data. The ES-C Timestamp attribute is an unsigned attribute. It is timestamp of a hash of the electronic signature and the complete validation data (ES-C). It is a special purpose TimeStampToken Attribute which timestamps the ES-C. Several instances instance of this attribute may occur with an electronic signature from different TSAs. The following object identifier identifies the ES-C Timestamp attribute: id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25} ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 35] Internet Draft Electronic Signature Formats The ES-C timestamp attribute value has the ASN.1 syntax ESCTimeStampToken. ESCTimeStampToken ::= TimeStampToken The value of messageImprint field within TimeStampToken must be a hash of the concatenated values (without the type or length encoding for that value) of the following data objects as present in the ES with Complete validation data (ES-C): * signature field within SignerInfo; * SignatureTimeStampToken attribute; * CompleteCertificateRefs attribute; * CompleteRevocationRefs attribute. For further information and definition of the Time Stamp Token see clause [TSP]. Temp note ;ref to timestamping doc required. 4.3.4 Time-Stamped Certificates and CRLs Attribute Definition This attribute is used for the Type 2 X-Timestamp validation data. A TimestampedCertsCRLsRef attribute is an unsigned attribute. It is a list of referenced certificates and OCSP responses/CRLs which are been timestamped to protect against certain CA compromises. Its syntax is as follows: The following object identifier identifies the TimestampedCertsCRLsRef attribute: id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 26} The attribute value has the ASN.1 syntax TimestampedCertsCRLs. TimestampedCertsCRLs ::= TimeStampToken The value of messageImprint field within TimeStampToken must be a hash of the concatenated values (without the type or length encoding for that value) of the following data objects as present in the ES with Complete validation data (ES-C): * CompleteCertificateRefs attribute; * CompleteRevocationRefs attribute. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 36] Internet Draft Electronic Signature Formats 4.4 Archive Validation Data Where an electronic signature is required to last for a very long time, and a the timestamp on an electronic signature is in danger of being invalidated due to algorithm weakness or limits in the validity period of the TSA certificate, then it may be required to timestamp the electronic signature several times. When this is required an archive timestamp attribute may be required. This timestamp may be repeatedly applied over a period of time. 4.4.1 Archive Timestamp Attribute Definition The Archive Timestamp attribute is timestamp of the user data and the entire electronic signature. If the Certificate values and Revocation Values attributes are not present these attributes must be added to the electronic signature prior to the timestamp. The Archive Timestamp attribute is an unsigned attribute. Several instances of this attribute may occur with on electronic signature both over time and from different TSAs. The following object identifier identifies the Nested Archive Timestamp attribute: id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 27} Archive timestamp attribute values have the ASN.1 syntax ArchiveTimeStampToken ArchiveTimeStampToken ::= TimeStampToken The value of messageImprint field within TimeStampToken must be a hash of the concatenated values (without the type or length encoding for that value) of the following data objects as present in the electronic signature: * encapContentInfo eContent OCTET STRING; * signedAttributes; * signature field within SignerInfo; * SignatureTimeStampToken attribute; * CompleteCertificateRefs attribute; * CompleteRevocationData attribute; * CertificateValues attribute (If not already present this information must be included in the ES-A); * RevocationValues attribute (If not already present this information must be included in the ES-A); * ESCTimeStampToken attribute if present; * TimestampedCertsCRLs attribute if present; * any previous ArchiveTimeStampToken attributes. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 37] Internet Draft Electronic Signature Formats For further information and definition of TimeStampToken see see [TSP] Temp note ;ref to timestamping doc required The timestamp should be created using stronger algorithms (or longer key lengths) than in the original electronic signatures and weak algorithm (key length) timestamps . 5. Signature Policy Specification This document mandates that: * an electronic signature must be processed by the signer and verifier in accordance with the signature policy as identified by the signature policy attribute (see clause 4.1); * the signature policy must be identifiable by an Object Identifier; * there must exist a specification of the signature policy; * for a given signature policy there must be one definitive form of the specification which has a unique binary encoding; * a hash of the definitive specification, using an agreed algorithm, must be provided by the signer and checked by the verifier (see clause 4.1). A signature policy specification includes general information about the policy, the validation policy rules and other signature policy information. Clause 6 describes the kind of information to be included in a signature policy. The current document does not mandate the form of the signature policy specification. The signature policy may be specified either: * in a free form document for human interpretation; or * in a structured form using an agreed syntax and encoding. This document defines an ASN.1 based syntax that may be used to define a structured signature policy. 5.1 Overall ASN.1 Structure The overall structure of a signature policy defined using ASN.1 is given in this clause. Use of this ASN.1 structure is optional. This ASN.1 syntax is encoded using the Distinguished Encoding Rules (DER). ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 38] Internet Draft Electronic Signature Formats In this structure the policy information is preceded by an identifier for the hashing algorithm used to protect the signature policy and followed by the hash value which must be re-calculated and checked whenever the policy is passed between the issuer and signer/verifier. The hash is calculated without the outer type and length fields. SignaturePolicy ::= SEQUENCE { signPolicyHashAlg AlgorithmIdentifier, signPolicyInfo SignPolicyInfo, signPolicyHash SignPolicyHash OPTIONAL } SignPolicyHash ::= OCTET STRING SignPolicyInfo ::= SEQUENCE { signPolicyIdentifier SignPolicyId, dateOfIssue GeneralizedTime, policyIssuerName PolicyIssuerName, fieldOfApplication FieldOfApplication, signatureValidationPolicy SignatureValidationPolicy, signPolExtensions SignPolExtensions OPTIONAL } SignPolicyId ::= OBJECT IDENTIFIER The policyIssuerName field identifies the policy issuer in one or more of the general name forms. PolicyIssuerName ::= GeneralNames The fieldofApplication is a description of the expected application of this policy. FieldOfApplication ::= DirectoryString The signature validation policy rules are fully processable to allow the validation of electronic signatures issued under that signature policy. They are described in the rest of this clause. 5.2 Signature Validation Policy The signature validation policy defines for the signer which data elements must be present in the electronic signature he provides and for the verifier which data elements must be present under that signature policy for an electronic signature to be potentially valid. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 39] Internet Draft Electronic Signature Formats The signature validation policy is described as follows: SignatureValidationPolicy ::= SEQUENCE { signingPeriod SigningPeriod, commonRules CommonRules, commitmentRules CommitmentRules, signPolExtensions SignPolExtensions OPTIONAL } The signingPeriod identifies the date and time before which the signature policy should not be used for creating signatures, and an optional date after which it should not be used for creating signatures. SigningPeriod ::= SEQUENCE { notBefore GeneralizedTime, notAfter GeneralizedTime OPTIONAL } 5.3 Common Rules The CommonRules define rules that are common to all commitment types. These rules are defined in terms of trust conditions for certificates, timestamps and attributes, along with any constraints on attributes that may be included in the electronic signature. CommonRules ::= SEQUENCE { signerAndVeriferRules [0] SignerAndVerifierRules OPTIONAL, signingCertTrustCondition [1] SigningCertTrustCondition OPTIONAL, timeStampTrustCondition [2] TimestampTrustCondition OPTIONAL, attributeTrustCondition [3] AttributeTrustCondition OPTIONAL, algorithmConstraintSet [4] AlgorithmConstraintSet OPTIONAL, signPolExtensions [5] SignPolExtensions OPTIONAL } If a field is present in CommonRules then the equivalent field must not be present in any of the CommitmentRules (see below). If any of the following fields are not present in CommonRules then it must be present in each CommitmentRule: * signerAndVeriferRules; * signingCertTrustCondition; * timeStampTrustCondition. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 40] Internet Draft Electronic Signature Formats 5.4 Commitment Rules The CommitmentRules consists of the validation rules which apply to given commitment types: CommitmentRules ::= SEQUENCE OF CommitmentRule The CommitmentRule for given commitment types are defined in terms of trust conditions for certificates, timestamps and attributes, along with any constraints on attributes that may be included in the electronic signature. CommitmentRule ::= SEQUENCE { selCommitmentTypes SelectedCommitmentTypes, signerAndVeriferRules [0] SignerAndVerifierRules OPTIONAL, signingCertTrustCondition [1] SigningCertTrustCondition OPTIONAL, timeStampTrustCondition [2] TimestampTrustCondition OPTIONAL, attributeTrustCondition [3] AttributeTrustCondition OPTIONAL, algorithmConstraintSet [4] AlgorithmConstraintSet OPTIONAL, signPolExtensions [5] SignPolExtensions OPTIONAL } SelectedCommitmentTypes ::= SEQUENCE OF CHOICE { empty NULL, recognizedCommitmentType CommitmentType } If the SelectedCommitmentTypes indicates "empty" then this rule applied when a commitment type is not present (i.e.the type of commitment is indicated in the semantics of the message). Otherwise, the electronic signature must contain a commitment type indication that must fit one of the commitments types that are mentioned in CommitmentType. A specific commitment type identifier must not appear in more than one commitment rule. CommitmentType ::= SEQUENCE { identifier CommitmentTypeIdentifier, fieldOfApplication [0] FieldOfApplication OPTIONAL, semantics [1] DirectoryString OPTIONAL } The fieldOfApplication and semantics fields define the specific use and meaning of the commitment within the overall field of application defined for the policy. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 41] Internet Draft Electronic Signature Formats 5.5 Signer and Verifier Rules The SignerAndVerifierRules consists of signer rule and verification rules as defined below: SignerAndVerifierRules ::= SEQUENCE { signerRules SignerRules, verifierRules VerifierRules } 5.5.1 Signer Rules The signer rules identify: * if the eContent is empty and the signature is calculated using a hash of signed data external to CMS structure. * the CMS signed attributes that must be provided by the signer under this policy; * the CMS unsigned attribute that must be provided by the signer under this policy; * whether the certificate identifiers from the full certification path up to the trust point must be provided by the signer in the SigningCertificate attribute; * whether a signer's certificate, or all certificates in the certification path to the trust point must be provided by the signer in the certificates field of SignedData. SignerRules ::= SEQUENCE { externalSignedData BOOLEAN OPTIONAL, -- True if signed data is external to CMS structure -- False if signed data part of CMS structure -- not present if either allowed mandatedSignedAttr CMSAttrs, -- Mandated CMS signed attributes mandatedUnsignedAttr CMSAttrs, -- Mandated CMS unsigned attributed mandatedCertificateRef [0] CertRefReq DEFAULT signerOnly, -- Mandated Certificate Reference mandatedCertificateInfo [1] CertInfoReq DEFAULT none, -- Mandated Certificate Info signPolExtensions [2] SignPolExtensions OPTIONAL } CMSAttrs ::= SEQUENCE OF OBJECT IDENTIFIER The mandatedSignedAttr field must include the object identifier for all those signed attributes required by this document as well as additional attributes required by this policy. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 42] Internet Draft Electronic Signature Formats The mandatedUnsignedAttr field must include the object identifier for all those unsigned attributes required by this document as well as additional attributes required this policy. For example, if a signature timestamp (see clause 1.1) is required by the signer the object identifier for this attribute must be included. The mandatedCertificateRef identifies whether just the signer's certificate, or all the full certificate path must be provided by the signer. CertRefReq ::= ENUMERATED { signerOnly (1), -- Only reference to signer cert mandated fullPath (2) -- References for full cert path up to a trust point required } The mandatedCertificateInfo field identifies whether a signer's certificate, or all certificates in the certification path to the trust point must be provided by the signer in the certificates field of SignedData. CertInfoReq ::= ENUMERATED { none (0) , -- No mandatory requirements signerOnly (1) , -- Only reference to signer cert mandated fullPath (2) -- References for full cert path up to a -- trust point mandated } 5.5.2 Verifier Rules The verifier rules identify: * The CMS unsigned attributes that must be present under this policy and must be added by the verifier if not added by the signer. VerifierRules ::= SEQUENCE { mandatedUnsignedAttr MandatedUnsignedAttr, signPolExtensions SignPolExtensions OPTIONAL } MandatedUnsignedAttr ::= CMSAttrs -- Mandated CMS unsigned attributed ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 43] Internet Draft Electronic Signature Formats 5.6 Certificate and Revocation Requirement The SigningCertTrustCondition, TimestampTrustCondition and AttributeTrustCondition (defined in subsequent sub-clauses) make use of two ASN1 structures which are defined below: CertificateTrustTrees and CertRevReq. 5.6.1 Certificate Requirements The certificateTrustTrees identifies a set of self signed certificates for the trust points used to start (or end) certificate path processing and the initial conditions for certificate path validation as defined RFC 2459 [7] section 5. This ASN1 structure is used to define policy for validating the signing certificate, the TSA's certificate and attribute certificates. CertificateTrustTrees ::= SEQUENCE OF CertificateTrustPoint CertificateTrustPoint ::= SEQUENCE { trustpoint Certificate, -- self-signed certificate pathLenConstraint [0] PathLenConstraint OPTIONAL, acceptablePolicySet [1] AcceptablePolicySet OPTIONAL, -- If not present "any policy" nameConstraints [2] NameConstraints OPTIONAL, policyConstraints [3] PolicyConstraints OPTIONAL } The trustPoint field gives the self signed certificate for the CA that is used as the trust point for the start of certificate path processing. The pathLenConstraint field gives the maximum number of CA certificates that may be in a certification path following the trustpoint. A value of zero indicates that only the given trustpoint certificate and an end-entity certificate may be used. If present, the pathLenConstraint field must be greater than or equal to zero. Where pathLenConstraint is not present, there is no limit to the allowed length of the certification path. PathLenConstraint ::= INTEGER (0..MAX) The acceptablePolicySet field identifies the initial set of certificate policies, any of which are acceptable under the signature policy. AcceptablePolicySet ::= SEQUENCE OF CertPolicyId CertPolicyId ::= OBJECT IDENTIFIER ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 44] Internet Draft Electronic Signature Formats The nameConstraints field indicates a name space within which all subject names in subsequent certificates in a certification path must be located. Restrictions may apply to the subject distinguished name or subject alternative names. Restrictions apply only when the specified name form is present. If no name of the type is in the certificate, the certificate is acceptable. Restrictions are defined in terms of permitted or excluded name subtrees. Any name matching a restriction in the excludedSubtrees field is invalid regardless of information appearing in the ermittedSubtrees. NameConstraints ::= SEQUENCE { permittedSubtrees [0] GeneralSubtrees OPTIONAL, excludedSubtrees [1] GeneralSubtrees OPTIONAL } GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree GeneralSubtree ::= SEQUENCE { base GeneralName, minimum [0] BaseDistance DEFAULT 0, maximum [1] BaseDistance OPTIONAL } BaseDistance ::= INTEGER (0..MAX) The policyConstraints extension constrains path processing in two ways. It can be used to prohibit policy mapping or require that each certificate in a path contain an acceptable policy identifier. The policyConstraints field, if present specifies requirement for explicit indication of the certificate policy and/or the constraints on policy mapping. PolicyConstraints ::= SEQUENCE { requireExplicitPolicy [0] SkipCerts OPTIONAL, inhibitPolicyMapping [1] SkipCerts OPTIONAL } SkipCerts ::= INTEGER (0..MAX) If the inhibitPolicyMapping field is present, the value indicates the number of additional certificates that may appear in the path (including the trustpoint's self certificate) before policy mapping is no longer permitted. For example, a value of one indicates that policy mapping may be processed in certificates issued by the subject of this certificate, but not in additional certificates in the path. If the requireExplicitPolicy field is present, subsequent certificates must include an acceptable policy identifier. The value of requireExplicitPolicy indicates the number of additional certificates that may appear in the path (including the trustpoint's self certificate) before an explicit policy is required. An acceptable policy identifier is the identifier of a policy required by the user of the certification path or the identifier of a policy which has been declared equivalent through policy mapping. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 45] Internet Draft Electronic Signature Formats 5.6.2 Revocation Requirements The RevocRequirements field specifies minimum requirements for revocation information, obtained through CRLs and/or OCSP responses, to be used in checking the revocation status of certificates. This ASN1 structure is used to define policy for validating the signing certificate, the TSA's certificate and attribute certificates. CertRevReq ::= SEQUENCE { endCertRevReq RevReq, caCerts [0] RevReq } Certificate revocation requirements are specified in terms of checks required on: * endCertRevReq: end certificates (i.e. the signers certificate, the attribute certificate or the timestamping authority certificate). * caCerts: CA certificates. RevReq ::= SEQUENCE { enuRevReq EnuRevReq, exRevReq SignPolExtensions OPTIONAL} An authority certificate is certificate issued to an authority (e.g. either to a certification authority or to an attribute authority (AA)). A TimeStamping Authority (TSA) is a trusted third party that creates time stamp tokens in order to indicate that a datum existed at a particular point in time (RFC??: "Internet X.509 Public Key Infrastructure - Time Stamp Protocol"). EnuRevReq ::= ENUMERATED { clrCheck (0), --Checks must be made against current CRLs -- (or authority revocation lists (ARL)) ocspCheck (1), -- The revocation status must be checked -- using the Online Certificate Status Protocol -- (OCSP),RFC 2450. bothCheck (2), -- Both CRL and OCSP checks must be carried out eitherCheck (3), -- At least one of CRL or OCSP checks must be -- carried out noCheck (4), -- no check is mandated other (5) -- Other mechanism as defined by signature poilicy -- extension } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 46] Internet Draft Electronic Signature Formats Revocation requirements are specified in terms of: * clrCheck: Checks must be made against current CRLs (or authority revocation lists); * ocspCheck: The revocation status must be checked using the Online Certificate Status Protocol (RFC 2450); * bothCheck: Both OCSP and CRL checks must be carried out; * eitherCheck: Either OCSP or CRL checks must be carried out; * noCheck: No check is mandated. 5.7 Signing Certificate Trust Conditions The SigningCertTrustCondition field identifies trust conditions for certificate path processing used to validate the signing certificate. SigningCertTrustCondition ::= SEQUENCE { signerTrustTrees CertificateTrustTrees, signerRevReq CertRevReq } 5.8 TimeStamp Trust Conditions The TimeStampTrustCondition field identifies trust conditions for certificate path processing used to authenticate the timstamping authority and constraints on the name of the timestamping authority. This applies to the timestamp that must be present in every ES-T. TimestampTrustCondition ::= SEQUENCE { ttsCertificateTrustTrees [0] CertificateTrustTrees OPTIONAL, ttsRevReq [1] CertRevReq OPTIONAL, ttsNameConstraints [2] NameConstraints OPTIONAL, cautionPeriod [3] DeltaTime OPTIONAL, signatureTimestampDelay [4] DeltaTime OPTIONAL } DeltaTime ::= SEQUENCE { deltaSeconds INTEGER, deltaMinutes INTEGER, deltaHours INTEGER, deltaDays INTEGER } If ttsCertificateTrustTrees is not present then the same rule as defined in certificateTrustCondition applies to certification of the timestamping authorities public key. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 47] Internet Draft Electronic Signature Formats The tstrRevReq specifies minimum requirements for revocation information, obtained through CRLs and/or OCSP responses, to be used in checking the revocation status of the time stamp that must be present in the ES-T. If ttsNameConstraints is not present then there are no additional naming constraints on the trusted timestamping authority other than those implied by the ttsCertificateTrustTrees. The cautionPeriod field specifies a caution period after the signing time that it is mandated the verifier must wait to get high assurance of the validity of the signer's key and that any relevant revocation has been notified. The revocation status information forming the ES with Complete validation data must not be collected and used to validate the electronic signature until after this caution period. The signatureTimestampDelay field specifies a maximum acceptable time between the signing time and the time at which the signature timestamp, as used to form the ES Timestamped, is created for the verifier. If the signature timestamp is later that the time in the signing-time attribute by more than the value given in signatureTimestampDelay, the signature must be considered invalid. 5.9 Attribute Trust Conditions If the attributeTrustCondition field is not present then any certified attributes may not considered to be valid under this validation policy. The AttributeTrustCondition field is defined as follows: AttributeTrustCondition ::= SEQUENCE { attributeMandated BOOLEAN, -- Attribute must be present howCertAttribute HowCertAttribute, attrCertificateTrustTrees [0] CertificateTrustTrees OPTIONAL, attrRevReq [1] CertRevReq OPTIONAL, attributeConstraints [2] AttributeConstraints OPTIONAL } If attributeMandated is true then an attribute, certified within the following constraints, must be present. If false, then the signature is still valid if no attribute is specified. The howCertAttribute field specifies whether attributes uncertified attributes "claimed" by the signer, or certified in an attribute certificate or either using the signer attributes attribute defined in 4.12.3. HowCertAttribute ::= ENUMERATED { claimedAttribute (0), certifiedAttribtes (1), either (2) } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 48] Internet Draft Electronic Signature Formats The attrCertificateTrustTrees specifies certificate path conditions for any attribute certificate. If not present the same rules apply as in certificateTrustCondition. The attrRevReq specifies minimum requirements for revocation information, obtained through CRLs and/or OCSP responses, to be used in checking the revocation status of Attribute Certificates, if any are present. If the attributeConstraints field is not present then there are no constraints on the attributes that may be validated under this policy. The attributeConstraints field is defined as follows: AttributeConstraints ::= SEQUENCE { attributeTypeConstarints [0] AttributeTypeConstraints OPTIONAL, attributeValueConstarints [1] AttributeValueConstraints OPTIONAL } If present, the attributeTypeConstarints field specifies the attribute types which are considered valid under the signature policy. Any value for that attribute is considered valid. AttributeTypeConstraints ::= SEQUENCE OF AttributeType If present, the attributeTypeConstraints field specifies the specific attribute values which are considered valid under the signature policy. AttributeValueConstraints ::= SEQUENCE OF AttributeTypeAndValue 5.10 Algorithm Constraints The algorithmConstrains fields, if present, identifies the signing algorithms (hash, public key cryptography, combined hash and public key cryptography) that may be used for specific purposes and any minimum length. If this field is not present then the policy applies no constraints. AlgorithmConstraintSet ::= SEQUENCE { -- Algorithm constrains on: signerAlgorithmConstraints [0] AlgorithmConstraints OPTIONAL, -- signer eeCertAlgorithmConstraints [1] AlgorithmConstraints OPTIONAL, -- issuer of end entity certs. caCertAlgorithmConstraints [2] AlgorithmConstraints OPTIONAL, -- issuer of CA certificates aaCertAlgorithmConstraints [3] AlgorithmConstraints OPTIONAL, -- Attribute Authority tsaCertAlgorithmConstraints [4] AlgorithmConstraints OPTIONAL -- TimeStamping Authority } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 49] Internet Draft Electronic Signature Formats AlgorithmConstraints ::= SEQUENCE OF AlgAndLength AlgAndLength ::= SEQUENCE { algID OBJECT IDENTIFIER, minKeyLength INTEGER OPTIONAL, -- Minimum key length in bits other SignPolExtensions OPTIONAL } An Attribute Authority (AA)is authority which assigns privileges by issuing attribute certificates 5.11 Signature Policy Extensions Additional signature policy rules may be added to: * the overall signature policy structure, as defined in clause 5.1; * the signature validation policy structure, as defined in clause 5.2; * the common rules, as defined in clause 5.3; * the commitment rules, as defined in clause 5.4; * the signer rules, as defined in clause 5.5.1; * the verifier rules, as defined in clause 5.5.2; * the revocation requirements in clause 5.6.2; * the algorithm constraints in clause 5.10. These extensions to the signature policy rules must be defined using an ASN.1 syntax with an associated object identifier carried in the SignPolExtn as defined below: SignPolExtensions ::= SEQUENCE OF SignPolExtn SignPolExtn ::= SEQUENCE { extnID OBJECT IDENTIFIER, extnValue OCTET STRING } The extnID field must contain the object identifier for the extension. The extnValue field must contain the DER (see ITU-T Recommendation X.690 [4]) encoded value of the extension. The definition of an extension, as identified by extnID must include a definition of the syntax and semantics of the extension. 6. Security considerations 6.1 Protection of Private Key The security of the electronic signature mechanism defined in this document depends on the privacy of the signer's private key. Implementations must take steps to ensure that private keys cannot be compromised. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 50] Internet Draft Electronic Signature Formats 6.2 Choice of Algorithms Implementers should be aware that cryptographic algorithms become weaker with time. As new cryptoanalysis techniques are developed and computing performance improves, the work factor to break a particular cryptographic algorithm will reduce. Therefore, cryptographic algorithm implementations should be modular allowing new algorithms to be readily inserted. That is, implementers should be prepared for the set of mandatory to implement algorithms to change over time. 7. Conformance Requirements This document only defines conformance requirements up to a ES with Complete validation data (ES-C). This means that none of the extended and archive forms of Electronic Signature (ES-X, ES-A) need to be implemented to get conformance to this standard. This document mandates support for elements of the signature policy. 7.1 Signer A system supporting signers according to this document must, at a minimum, support generation of an electronic signature consisting of the following components: * The general CMS syntax and content type as defined in RFC 2630 (see clauses 4.1 and 4.2). * CMS SignedData as defined in RFC 2630 with version set to 3 and at least one SignerInfo must be present (see clauses 4.3, 4.4, 4.5, 4.6). * The following CMS Attributes as defined in RFC 2630 : - ContentType; This must always be present (see clause 3.7.1); - MessageDigest; This must always be present (see clause 3.7.2); - SigningTime; This must always be present (see clause 3.7.3). * The following ESS Attributes as defined in RFC 2634 : - SigningCertificate: This must be set as defined in clauses 3.8.1 and 3.8.2. * The following Attributes as defined in clause 3.9: - SignaturePolicyIdentifier; This must always be present. * Public Key Certificates as defined in ITU-T Recommendation X.509 [1] and profiled in RFC 2459 [7] (see clause 9.1). ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 51] Internet Draft Electronic Signature Formats 7.2 Verifier A system supporting verifiers according to this document must, at a minimum, support: * Verification of the mandated components of an electronic signature, as defined in clause 14.1. * Signature Timestamp attribute, as defined in clause 5.1.1. * Complete Certificate Refs attribute, as defined in clause 5.2.1. * Complete Revocation Refs Attribute, as defined in clause 5.2.2. * Public Key Certificates, as defined in ITU-T Recommendation X.509 and profiled in RFC 2459 (see clause 10.1) * Either of: - Certificate Revocation Lists. as defined in ITU-T Recommendation X.509 [1] and profiled in RFC 2459 [7] (see clause 10.2); Or - On-line Certificate Status Protocol, as defined in RFC 2560 (see clause 10.3). 7.3 Signature Policy Both signer and verifier systems must be able to process an electronic signature in accordance with the specification of at least one signature policy, as identified by the signature policy attribute (see clause 4.9.1). 8. References [RFC2510] C. Adams, S. Farrell, "Internet X.509 Public Key Infrastructure, Certificate Management Protocols," RFC 2510, March 1999. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2246] T. Dierks, C. Allen, "The TLS Protocol, Version 1.0," RFC 2246, January 1999. [RFC 2634] P. Hoffman, "Enhanced Security Services for S/MIME", [RFC 2630] R. Housley, "Cryptographic Message Syntax", RFC 2630, June 1999. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 52] Internet Draft Electronic Signature Formats [RFC2459] R. Housley, W. Ford, W. Polk, D. Solo, "Internet X.509 Public Key Infrastructure, Certificate and CRL Profile," RFC 2459, January 1999. [PKCS9] RSA Laboratories, "The Public-Key Cryptography Standards (PKCS)", RSA Data Security Inc., Redwood City, California, November 1993 Release. [ISONR] ISO/IEC 10181-5: Security Frameworks in Open Systems. Non-Repudiation Framework. April 1997. 9. Authors' Addresses This Informational RFC has been produced in ETSI TC-SEC. ETSI F-06921 Sophia Antipolis, Cedex - FRANCE 650 Route des Lucioles - Sophia Antipolis Valbonne - France Tel: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16 secretariat@etsi.fr http://www.etsi.org ETSI Contact Point Harri Rasilainen ETSI F-06921 Sophie Antipolis 650 Route des Lucioles Sophia Antipolis, Valbonne FRANCE harri.rasilainen@etsi.fr Additional Contact Points John Ross Security & Standards 192 Moulsham Street Chelmsford, Essex CM2 0LG United Kingdom ross@secstan.com Denis Pinkas Nick Pope Bull S.A. Security & Standards 12, rue de Paris 192 Moulsham Street B.P. 59 Chelmsford, Essex 78231 Le Pecq CM2 0LG FRANCE United Kingdom pinkas.denis@bull.net pope@secstan.com ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 53] Internet Draft Electronic Signature Formats 10. Full Copyright Statement Copyright (C) The Internet Society (2000). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 11.Temportary Issues It might be interesting to split this document into two RFCs, one RFC dealing only with ES formats, the other one only with Signature Policies. In such a case, the basis of this split will be, sections 6 and annex C will be removed from this document and placed in the another RFC dealing with Signature policies. The signature policy ASN.1 will be removed the current ASN.1 modules in annex A and placed in a new ASN.1 module in the other RFC dealing with Signature Policies. Opinions are requested on this issue. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 54] Internet Draft Electronic Signature Formats Note: If there is a request to split this document into two RFCs, one RFC dealing with ES formats, the other with Signature policies, then the signature policy ASN.1 will be removed the current ASN.1 modules in annex A and placed in a new ASN.1 module in the other RFC dealing with Signature policies. Annex A (normative): ASN.1 Definitions This annex provides a summary of all the ASN.1 syntax definitions for new syntax defined in this document. A.1 Definitions Using X.208 (1988) ASN.1 Syntax NOTE: The ASN.1 module defined in clause A.1 has precedence over that defined in Annex A-2 in the case of any conflict. ETS-ElectronicSignature-88syntax { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 5} DEFINITIONS EXPLICIT TAGS ::= BEGIN -- EXPORTS All - IMPORTS -- Crypographic Message Syntax (CMS): RFC 2630 ContentInfo, ContentType, id-data, id-signedData, SignedData, EncapsulatedContentInfo, SignerInfo, id-contentType, id-messageDigest, MessageDigest, id-signingTime, SigningTime, id-countersignature, Countersignature FROM CryptographicMessageSyntax { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) cms(1) } -- ESS Defined attributes: RFC 2634 -- (Enhanced Security Services for S/MIME) id-aa-signingCertificate, SigningCertificate, IssuerSerial, id-aa-contentReference, ContentReference, id-aa-contentIdentifier, ContentIdentifier FROM ExtendedSecurityServices { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 55] Internet Draft Electronic Signature Formats -- Internet X.509 Public Key Infrastructure - - Certificate and CRL Profile: RFC 2459 Certificate, AlgorithmIdentifier, CertificateList, Name, GeneralNames, GeneralName, DirectoryString,Attribute, AttributeTypeAndValue, AttributeType, AttributeValue, PolicyInformation, BMPString, UTF8String FROM PKIX1Explicit88 {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit- 88(1)} -- X.509 '97 Authentication Framework AttributeCertificate FROM AuthenticationFramework {joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3} -- The imported AttributeCertificate is defined using the X.680 1997 -- ASN.1 Syntax, -- an equivalent using the 88 ASN.1 syntax may be used. -- OCSP 2560 BasicOCSPResponse, ResponderID FROM OCSP {-- OID not assigned -- } -- Time Stamp Protocol Internet Draft -- TimeStampToken FROM TSP {-- OID not assigned -- }; -- S/MIME Object Identifier arcs used in this document -- ================================================================== -- S/MIME OID arc used in this document -- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2) -- us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 } -- S/MIME Arcs -- id-mod OBJECT IDENTIFIER ::= { id-smime 0 } -- modules -- id-ct OBJECT IDENTIFIER ::= { id-smime 1 } -- content types -- id-aa OBJECT IDENTIFIER ::= { id-smime 2 } -- attributes -- id-spq OBJECT IDENTIFIER ::= { id-smime 5 } -- signature policy qualifier -- id-cti OBJECT IDENTIFIER ::= { id-smime 6 } -- commitment type identifier ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 56] Internet Draft Electronic Signature Formats -- Definitions of Object Identifier arcs used in this document -- ================================================================== -- The allocation of OIDs to specific objects are given below with the -- associated ASN.1 syntax definition -- OID used referencing electronic signature mechanisms based on this -- standard for use with the IDUP API (see annex D) id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::= { itu-t(0) identified-organization(4) etsi(0) electronic-signature-standard (1733) part1 (1) idupMechanism (4)etsiESv1(1) } -- CMS Attributes Defined in this document -- ============================================== -- Mandatory Electronic Signature Attributes -- OtherSigningCertificate id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-aa(2) 19 } OtherSigningCertificate ::= SEQUENCE { certs SEQUENCE OF OtherCertID, policies SEQUENCE OF PolicyInformation OPTIONAL -- NOT USED IN THIS DOCUMENT } OtherCertID ::= SEQUENCE { otherCertHash OtherHash, issuerSerial IssuerSerial OPTIONAL } OtherHash ::= CHOICE { sha1Hash OtherHashValue, -- This contains a SHA-1 hash otherHash OtherHashAlgAndValue} OtherHashValue ::= OCTET STRING OtherHashAlgAndValue ::= SEQUENCE { hashAlgorithm AlgorithmIdentifier, hashValue OtherHashValue } -- Signature Policy Identifier id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-aa(2) 15 } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 57] Internet Draft Electronic Signature Formats SignaturePolicyIdentifier ::= SEQUENCE { sigPolicyIdentifier SigPolicyId, sigPolicyHash SigPolicyHash, sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF SigPolicyQualifierInfo OPTIONAL} SigPolicyId ::= OBJECT IDENTIFIER SigPolicyHash ::= ETSIHashAlgAndValue SigPolicyQualifierInfo ::= SEQUENCE { sigPolicyQualifierId SigPolicyQualifierId, sigQualifier ANY DEFINED BY sigPolicyQualifierId } SigPolicyQualifierId ::= OBJECT IDENTIFIER id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-spq(5) 1 } SPuri ::= IA5String id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-spq(5) 2 } SPUserNotice ::= SEQUENCE { noticeRef NoticeReference OPTIONAL, explicitText DisplayText OPTIONAL} NoticeReference ::= SEQUENCE { organization DisplayText, noticeNumbers SEQUENCE OF INTEGER } DisplayText ::= CHOICE { visibleString VisibleString (SIZE (1..200)), bmpString BMPString (SIZE (1..200)), utf8String UTF8String (SIZE (1..200)) } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 58] Internet Draft Electronic Signature Formats -- Optional Electronic Signature Attributes -- Commitment Type id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16} CommitmentTypeIndication ::= SEQUENCE { commitmentTypeId CommitmentTypeIdentifier, commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF CommitmentTypeQualifier OPTIONAL} CommitmentTypeIdentifier ::= OBJECT IDENTIFIER CommitmentTypeQualifier ::= SEQUENCE { commitmentTypeIdentifier CommitmentTypeIdentifier, qualifier ANY DEFINED BY commitmentTypeIdentifier } id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1} id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2} id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 3} id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4} id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 5} id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 6} ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 59] Internet Draft Electronic Signature Formats -- Signer Location id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17} SignerLocation ::= SEQUENCE { -- At least one of the following must be present countryName [0] DirectoryString OPTIONAL, -- As used to name a Country in X.500 localityName [1] DirectoryString OPTIONAL, -- As used to name a locality in X.500 postalAdddress [2] PostalAddress OPTIONAL } PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString -- Signer Attributes id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18} SignerAttribute ::= SEQUENCE OF CHOICE { claimedAttributes [0] ClaimedAttributes, certifiedAttributes [1] CertifiedAttributes } ClaimedAttributes ::= SEQUENCE OF Attribute CertifiedAttributes ::= AttributeCertificate -- As defined in X.509 : see section 10.3 -- Content Timestamp id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 20} ContentTimestamp::= TimeStampToken -- Validation Data -- Signature Timestamp id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 14} SignatureTimeStampToken ::= TimeStampToken ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 60] Internet Draft Electronic Signature Formats -- Complete Certificate Refs. id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21} CompleteCertificateRefs ::= SEQUENCE OF ETSICertID -- Complete Revocation Refs id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22} CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef CrlOcspRef ::= SEQUENCE { crlids [0] CRLListID OPTIONAL, ocspids [1] OcspListID OPTIONAL, otherRev [2] OtherRevRefs OPTIONAL } CRLListID ::= SEQUENCE { crls SEQUENCE OF CrlValidatedID} CrlValidatedID ::= SEQUENCE { crlHash ETSIHash, crlIdentifier CrlIdentifier OPTIONAL} CrlIdentifier ::= SEQUENCE { crlissuer Name, crlIssuedTime UTCTime, crlNumber INTEGER OPTIONAL } OcspListID ::= SEQUENCE { ocspResponses SEQUENCE OF OcspResponsesID} OcspResponsesID ::= SEQUENCE { ocspIdentifier OcspIdentifier, ocspRepHash ETSIHash OPTIONAL } OcspIdentifier ::= SEQUENCE { ocspResponderID ResponderID, -- As in OCSP response data producedAt GeneralizedTime -- As in OCSP response data } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 61] Internet Draft Electronic Signature Formats OtherRevRefs ::= SEQUENCE { otherRevRefType OtherRevRefType, otherRevRefs ANY DEFINED BY otherRevRefType } OtherRevRefType ::= OBJECT IDENTIFIER -- Certificate Values id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23} CertificateValues ::= SEQUENCE OF Certificate -- Certificate Revocation Values id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 24} RevocationValues ::= SEQUENCE { crlVals [0] SEQUENCE OF CertificateList OPTIONAL, ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL, otherRevVals [2] OtherRevVals } OtherRevVals ::= SEQUENCE { otherRevValType OtherRevValType, otherRevVals ANY DEFINED BY otherRevValType } OtherRevValType ::= OBJECT IDENTIFIER -- ES-C Timestamp id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25} ESCTimeStampToken ::= TimeStampToken -- Time-Stamped Certificates and CRLs id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 26} TimestampedCertsCRLs ::= TimeStampToken ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 62] Internet Draft Electronic Signature Formats -- Archive Timestamp id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member- body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 27} ArchiveTimeStampToken ::= TimeStampToken -- Signature Policy Specification -- ============================== SignaturePolicy ::= SEQUENCE { signPolicyHashAlg AlgorithmIdentifier, signPolicyInfo SignPolicyInfo, signPolicyHash SignPolicyHash OPTIONAL } SignPolicyHash ::= OCTET STRING SignPolicyInfo ::= SEQUENCE { signPolicyIdentifier SignPolicyId, dateOfIssue GeneralizedTime, policyIssuerName PolicyIssuerName, fieldOfApplication FieldOfApplication, signatureValidationPolicy SignatureValidationPolicy, signPolExtensions SignPolExtensions OPTIONAL } SignPolicyId ::= OBJECT IDENTIFIER PolicyIssuerName ::= GeneralNames FieldOfApplication ::= DirectoryString SignatureValidationPolicy ::= SEQUENCE { signingPeriod SigningPeriod, commonRules CommonRules, commitmentRules CommitmentRules, signPolExtensions SignPolExtensions OPTIONAL } SigningPeriod ::= SEQUENCE { notBefore GeneralizedTime, notAfter GeneralizedTime OPTIONAL } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 63] Internet Draft Electronic Signature Formats CommonRules ::= SEQUENCE { signerAndVeriferRules [0] SignerAndVerifierRules OPTIONAL, signingCertTrustCondition [1] SigningCertTrustCondition OPTIONAL, timeStampTrustCondition [2] TimestampTrustCondition OPTIONAL, attributeTrustCondition [3] AttributeTrustCondition OPTIONAL, algorithmConstraintSet [4] AlgorithmConstraintSet OPTIONAL, signPolExtensions [5] SignPolExtensions OPTIONAL } CommitmentRules ::= SEQUENCE OF CommitmentRule CommitmentRule ::= SEQUENCE { selCommitmentTypes SelectedCommitmentTypes, signerAndVeriferRules [0] SignerAndVerifierRules OPTIONAL, signingCertTrustCondition [1] SigningCertTrustCondition OPTIONAL, timeStampTrustCondition [2] TimestampTrustCondition OPTIONAL, attributeTrustCondition [3] AttributeTrustCondition OPTIONAL, algorithmConstraintSet [4] AlgorithmConstraintSet OPTIONAL, signPolExtensions [5] SignPolExtensions OPTIONAL } SelectedCommitmentTypes ::= SEQUENCE OF CHOICE { empty NULL, recognizedCommitmentType CommitmentType } CommitmentType ::= SEQUENCE { identifier CommitmentTypeIdentifier, fieldOfApplication [0] FieldOfApplication OPTIONAL, semantics [1] DirectoryString OPTIONAL } SignerAndVerifierRules ::= SEQUENCE { signerRules SignerRules, verifierRules VerifierRules } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 64] Internet Draft Electronic Signature Formats SignerRules ::= SEQUENCE { externalSignedData BOOLEAN OPTIONAL, -- True if signed data is external to CMS structure -- False if signed data part of CMS structure -- not present if either allowed mandatedSignedAttr CMSAttrs, -- Mandated CMS signed attributes mandatedUnsignedAttr CMSAttrs, -- Mandated CMS unsigned attributed mandatedCertificateRef [0] CertRefReq DEFAULT signerOnly, -- Mandated Certificate Reference mandatedCertificateInfo [1] CertInfoReq DEFAULT none, -- Mandated Certificate Info signPolExtensions [2] SignPolExtensions OPTIONAL} CMSAttrs ::= SEQUENCE OF OBJECT IDENTIFIER CertRefReq ::= ENUMERATED { signerOnly (1), -- Only reference to signer cert mandated fullPath (2) -- References for full cert path up to a trust point required } CertInfoReq ::= ENUMERATED { none (0), -- No mandatory requirements signerOnly (1), -- Only reference to signer cert mandated fullPath (2) -- References for full cert path up to a trust point mandated } VerifierRules ::= SEQUENCE { mandatedUnsignedAttr MandatedUnsignedAttr, signPolExtensions SignPolExtensions OPTIONAL } MandatedUnsignedAttr ::= CMSAttrs -- Mandated CMS unsigned attributed ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 65] Internet Draft Electronic Signature Formats CertificateTrustTrees ::= SEQUENCE OF CertificateTrustPoint CertificateTrustPoint ::= SEQUENCE { trustpoint Certificate, -- self-signed certificate pathLenConstraint [0] PathLenConstraint OPTIONAL, acceptablePolicySet [1] AcceptablePolicySet OPTIONAL, -- If not present "any policy" nameConstraints [2] NameConstraints OPTIONAL, policyConstraints [3] PolicyConstraints OPTIONAL } PathLenConstraint ::= INTEGER (0..MAX) AcceptablePolicySet ::= SEQUENCE OF CertPolicyId CertPolicyId ::= OBJECT IDENTIFIER NameConstraints ::= SEQUENCE { permittedSubtrees [0] GeneralSubtrees OPTIONAL, excludedSubtrees [1] GeneralSubtrees OPTIONAL } GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree GeneralSubtree ::= SEQUENCE { base GeneralName, minimum [0] BaseDistance DEFAULT 0, maximum [1] BaseDistance OPTIONAL } BaseDistance ::= INTEGER (0..MAX) PolicyConstraints ::= SEQUENCE { requireExplicitPolicy [0] SkipCerts OPTIONAL, inhibitPolicyMapping [1] SkipCerts OPTIONAL } SkipCerts ::= INTEGER (0..MAX) CertRevReq ::= SEQUENCE { endCertRevReq RevReq, caCerts [0] RevReq } RevReq ::= SEQUENCE { enuRevReq EnuRevReq, exRevReq SignPolExtensions OPTIONAL} ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 66] Internet Draft Electronic Signature Formats EnuRevReq ::= ENUMERATED { clrCheck (0), --Checks must be made against current CRLs -- (or authority revocation lists) ocspCheck (1), -- The revocation status must be checked -- using the Online Certificate Status Protocol (RFC 2450) bothCheck (2), -- Both CRL and OCSP checks must be carried out eitherCheck (3), -- At least one of CRL or OCSP checks must be carried out noCheck (4), -- no check is mandated other (5) -- Other mechanism as defined by signature policy extension } SigningCertTrustCondition ::= SEQUENCE { signerTrustTrees CertificateTrustTrees, signerRevReq CertRevReq } TimestampTrustCondition ::= SEQUENCE { ttsCertificateTrustTrees [0] CertificateTrustTrees OPTIONAL, ttsRevReq [1] CertRevReq OPTIONAL, ttsNameConstraints [2] NameConstraints OPTIONAL, cautionPeriod [3] DeltaTime OPTIONAL, signatureTimestampDelay [4] DeltaTime OPTIONAL } DeltaTime ::= SEQUENCE { deltaSeconds INTEGER, deltaMinutes INTEGER, deltaHours INTEGER, deltaDays INTEGER } AttributeTrustCondition ::= SEQUENCE { attributeMandated BOOLEAN, -- Attribute must be present howCertAttribute HowCertAttribute, attrCertificateTrustTrees [0] CertificateTrustTrees OPTIONAL, attrRevReq [1] CertRevReq OPTIONAL, attributeConstraints [2] AttributeConstraints OPTIONAL } HowCertAttribute ::= ENUMERATED { claimedAttribute (0), certifiedAttribtes (1), either (2) } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 67] Internet Draft Electronic Signature Formats AttributeConstraints ::= SEQUENCE { attributeTypeConstarints [0] AttributeTypeConstraints OPTIONAL, attributeValueConstarints [1] AttributeValueConstraints OPTIONAL } AttributeTypeConstraints ::= SEQUENCE OF AttributeType AttributeValueConstraints ::= SEQUENCE OF AttributeTypeAndValue AlgorithmConstraintSet ::= SEQUENCE { -- Algorithm constrains on: signerAlgorithmConstraints [0] AlgorithmConstraints OPTIONAL, -- signer eeCertAlgorithmConstraints [1] AlgorithmConstraints OPTIONAL, -- issuer of end entity certs. caCertAlgorithmConstraints [2] AlgorithmConstraints OPTIONAL, -- issuer of CA certificates aaCertAlgorithmConstraints [3] AlgorithmConstraints OPTIONAL, -- Attribute Authority tsaCertAlgorithmConstraints [4] AlgorithmConstraints OPTIONAL -- TimeStamping Authority } AlgorithmConstraints ::= SEQUENCE OF AlgAndLength AlgAndLength ::= SEQUENCE { algID OBJECT IDENTIFIER, minKeyLength INTEGER OPTIONAL, -- Minimum key length in bits other SignPolExtensions OPTIONAL } SignPolExtensions ::= SEQUENCE OF SignPolExtn SignPolExtn ::= SEQUENCE { extnID OBJECT IDENTIFIER, extnValue OCTET STRING } END -- ETS-ElectronicSignature-88syntax -- ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 68] Internet Draft Electronic Signature Formats A.2 Definitions Using X.680 1997 ASN.1 Syntax NOTE: The ASN.1 module defined in clause A.1 has precedence over that defined in clause A.2 in the case of any conflict. ETS-ElectronicSignature-97Syntax { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-mod(0) 6} DEFINITIONS EXPLICIT TAGS ::= BEGIN -- EXPORTS All - IMPORTS -- Crypographic Message Syntax (CMS): RFC 2630 ContentInfo, ContentType, id-data, id-signedData, SignedData, EncapsulatedContentInfo, SignerInfo, id-contentType, id-messageDigest, MessageDigest, id-signingTime, SigningTime, id-countersignature, Countersignature FROM CryptographicMessageSyntax { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) cms(1) } -- ESS Defined attributes: RFC 2634 (Enhanced Security Services -- for S/MIME) id-aa-signingCertificate, SigningCertificate, IssuerSerial, id-aa-contentReference, ContentReference, id-aa-contentIdentifier, ContentIdentifier FROM ExtendedSecurityServices { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) ess(2) } -- Internet X.509 Public Key Infrastructure - - Certificate and CRL Profile:RFC 2459 Certificate, AlgorithmIdentifier, CertificateList, Name, GeneralNames, GeneralName, DirectoryString, Attribute, AttributeTypeAndValue, AttributeType, AttributeValue, PolicyInformation. FROM PKIX1Explicit93 {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit-88(1)} -- X.509 '97 Authentication Framework AttributeCertificate FROM AuthenticationFramework {joint-iso-ccitt ds(5) module(1) authenticationFramework(7) 3} ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 69] Internet Draft Electronic Signature Formats -- OCSP 2560 BasicOCSPResponse, ResponderID FROM OCSP -- { OID not assigned } -- Time Stamp Protocol Internet Draft TimeStampToken FROM TSP -- { OID not assigned }; -- S/MIME Object Identifier arcs used in this document -- ================================================================== -- S/MIME OID arc used in this document -- id-smime OBJECT IDENTIFIER ::= { iso(1) member-body(2) -- us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 16 } -- S/MIME Arcs -- id-mod OBJECT IDENTIFIER ::= { id-smime 0 } -- modules -- id-ct OBJECT IDENTIFIER ::= { id-smime 1 } -- content types -- id-aa OBJECT IDENTIFIER ::= { id-smime 2 } -- attributes -- id-spq OBJECT IDENTIFIER ::= { id-smime 5 } -- signature policy qualifier -- id-cti OBJECT IDENTIFIER ::= { id-smime 6 } -- commitment type identifier -- Definitions of Object Identifier arcs used in this document -- ================================================================== -- The allocation of OIDs to specific objects are given below with the -- associated ASN.1 syntax definition -- OID used referencing electronic signature mechanisms based on this -- standard for use with the IDUP API (see annex D) id-etsi-es-IDUP-Mechanism-v1 OBJECT IDENTIFIER ::= { itu-t(0) identified-organization(4) etsi(0) electronic-signature-standard (1733) part1 (1) idupMechanism (4)etsiESv1(1) } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 70] Internet Draft Electronic Signature Formats -- CMS Attributes Defined in this document -- ============================================== -- Mandatory Electronic Signature Attributes -- OtherSigningCertificate id-aa-ets-otherSigCert OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-aa(2) 19 } OtherSigningCertificate ::= SEQUENCE { certs SEQUENCE OF OtherCertID, policies SEQUENCE OF PolicyInformation OPTIONAL -- NOT USED IN THIS DOCUMENT } OtherCertID ::= SEQUENCE { otherCertHash OtherHash, issuerSerial IssuerSerial OPTIONAL } OtherHash ::= CHOICE { sha1Hash OtherHashValue, -- This contains a SHA-1 hash otherHash OtherHashAlgAndValue} OtherHashValue ::= OCTET STRING OtherHashAlgAndValue ::= SEQUENCE { hashAlgorithm AlgorithmIdentifier, hashValue OtherHashValue } -- Signature Policy Identifier id-aa-ets-sigPolicyId OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-aa(2) 15 } SignaturePolicyIdentifier ::= SEQUENCE { sigPolicyIdentifier SigPolicyId, sigPolicyHash SigPolicyHash, sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF SigPolicyQualifierInfo OPTIONAL} ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 71] Internet Draft Electronic Signature Formats SigPolicyId ::= OBJECT IDENTIFIER SigPolicyHash ::= ETSIHashAlgAndValue SigPolicyQualifierInfo ::= SEQUENCE { sigPolicyQualifierId SIG-POLICY-QUALIFIER.&id ({SupportedSigPolicyQualifiers}), qualifier SIG-POLICY-QUALIFIER.&Qualifier ({SupportedSigPolicyQualifiers} {@sigPolicyQualifierId})OPTIONAL } SupportedSigPolicyQualifiers SIG-POLICY-QUALIFIER ::= { noticeToUser | pointerToSigPolSpec } SIG-POLICY-QUALIFIER ::= CLASS { &id OBJECT IDENTIFIER UNIQUE, &Qualifier OPTIONAL } WITH SYNTAX { SIG-POLICY-QUALIFIER-ID &id [SIG-QUALIFIER-TYPE &Qualifier] } noticeToUser SIG-POLICY-QUALIFIER ::= { SIG-POLICY-QUALIFIER-ID id-sqt-unotice SIG-QUALIFIER-TYPE SPUserNotice } pointerToSigPolSpec SIG-POLICY-QUALIFIER ::= { SIG-POLICY-QUALIFIER-ID id-sqt-uri SIG-QUALIFIER-TYPE SPuri } id-spq-ets-uri OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-spq(5) 1 } SPuri ::= IA5String id-spq-ets-unotice OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-spq(5) 2 } SPUserNotice ::= SEQUENCE { noticeRef NoticeReference OPTIONAL, explicitText DisplayText OPTIONAL} NoticeReference ::= SEQUENCE { organization DisplayText, noticeNumbers SEQUENCE OF INTEGER } DisplayText ::= CHOICE { visibleString VisibleString (SIZE (1..200)), bmpString BMPString (SIZE (1..200)), utf8String UTF8String (SIZE (1..200)) } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 72] Internet Draft Electronic Signature Formats -- Optional Electronic Signature Attributes -- Commitment Type id-aa-ets-commitmentType OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 16} CommitmentTypeIndication ::= SEQUENCE { commitmentTypeId CommitmentTypeIdentifier, commitmentTypeQualifier SEQUENCE SIZE (1..MAX) OF CommitmentTypeQualifier OPTIONAL} CommitmentTypeIdentifier ::= OBJECT IDENTIFIER CommitmentTypeQualifier ::= SEQUENCE { commitmentQualifierId COMMITMENT-QUALIFIER.&id, qualifier COMMITMENT-QUALIFIER.&Qualifier OPTIONAL } COMMITMENT-QUALIFIER ::= CLASS { &id OBJECT IDENTIFIER UNIQUE, &Qualifier OPTIONAL } WITH SYNTAX { COMMITMENT-QUALIFIER-ID &id [COMMITMENT-TYPE &Qualifier] } id-cti-ets-proofOfOrigin OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 1} id-cti-ets-proofOfReceipt OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 2} id-cti-ets-proofOfDelivery OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 3} id-cti-ets-proofOfSender OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 4} id-cti-ets-proofOfApproval OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 5} id-cti-ets-proofOfCreation OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) cti(6) 6} ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 73] Internet Draft Electronic Signature Formats -- Signer Location id-aa-ets-signerLocation OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 17} SignerLocation ::= SEQUENCE { -- at least one of the following must be present countryName [0] DirectoryString OPTIONAL, -- As used to name a Country in X.500 localityName [1] DirectoryString OPTIONAL, -- As used to name a locality in X.500 postalAdddress [2] PostalAddress OPTIONAL } PostalAddress ::= SEQUENCE SIZE(1..6) OF DirectoryString -- Signer Attributes id-aa-ets-signerAttr OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 18} SignerAttribute ::= SEQUENCE OF CHOICE { claimedAttributes [0] ClaimedAttributes, certifiedAttributes [1] CertifiedAttributes } ClaimedAttributes ::= SEQUENCE OF Attribute CertifiedAttributes ::= AttributeCertificate -- As defined in X.509 : see section 10.3 -- Content Timestamp id-aa-ets-contentTimestamp OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 20} ContentTimestamp::= TimeStampToken -- Validation Data -- Signature Timestamp id-aa-signatureTimeStampToken OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 14} SignatureTimeStampToken ::= TimeStampToken ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 74] Internet Draft Electronic Signature Formats -- Complete Certificate Refs. id-aa-ets-certificateRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 21} CompleteCertificateRefs ::= SEQUENCE OF ETSICertID -- Complete Revocation Refs id-aa-ets-revocationRefs OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 22} CompleteRevocationRefs ::= SEQUENCE OF CrlOcspRef CrlOcspRef ::= SEQUENCE { crlids [0] CRLListID OPTIONAL, ocspids [1] OcspListID OPTIONAL, otherRev [2] OtherRevRefs OPTIONAL } CRLListID ::= SEQUENCE { crls SEQUENCE OF CrlValidatedID} CrlValidatedID ::= SEQUENCE { crlHash ETSIHash, crlIdentifier CrlIdentifier OPTIONAL} CrlIdentifier ::= SEQUENCE { crlissuer Name, crlIssuedTime UTCTime, crlNumber INTEGER OPTIONAL } OcspListID ::= SEQUENCE { ocspResponses SEQUENCE OF OcspResponsesID} OcspResponsesID ::= SEQUENCE { ocspIdentifier OcspIdentifier, ocspRepHash ETSIHash OPTIONAL } OcspIdentifier ::= SEQUENCE { ocspResponderID ResponderID, -- As in OCSP response data producedAt GeneralizedTime -- As in OCSP response data } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 75] Internet Draft Electronic Signature Formats OtherRevRefs ::= SEQUENCE { otherRevRefType OTHER-REVOCATION-REF.&id, otherRevRefs OTHER-REVOCATION-REF.&Type } OTHER-REVOCATION-REF ::= CLASS { &Type, &id OBJECT IDENTIFIER UNIQUE } WITH SYNTAX { &Type ID &id } -- Certificate Values id-aa-ets-certValues OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 23} CertificateValues ::= SEQUENCE OF Certificate -- Certificate Revocation Values id-aa-ets-revocationValues OBJECT IDENTIFIER ::= { iso(1) member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 24} RevocationValues ::= SEQUENCE { crlVals [0] SEQUENCE OF CertificateList OPTIONAL, ocspVals [1] SEQUENCE OF BasicOCSPResponse OPTIONAL, otherRevVals [2] OtherRevVals } OtherRevVals ::= SEQUENCE { otherRevValType OTHER-REVOCATION-VAL.&id, otherRevVals OTHER-REVOCATION-VAL.&Type } OTHER-REVOCATION-VAL ::= CLASS { &Type, &id OBJECT IDENTIFIER UNIQUE } WITH SYNTAX { &Type ID &id } -- ES-C Timestamp id-aa-ets-escTimeStamp OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 25} ESCTimeStampToken ::= TimeStampToken ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 76] Internet Draft Electronic Signature Formats -- Time-Stamped Certificates and CRLs id-aa-ets-certCRLTimestamp OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 26} TimestampedCertsCRLs ::= TimeStampToken -- Archive Timestamp id-aa-ets-archiveTimestamp OBJECT IDENTIFIER ::= { iso(1) member-body(2)us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2) 27} ArchiveTimeStampToken ::= TimeStampToken -- Signature Policy Specification -- ============================== SignaturePolicy ::= SEQUENCE { signPolicyHashAlg AlgorithmIdentifier, signPolicyInfo SignPolicyInfo, signPolicyHash SignPolicyHash OPTIONAL } SignPolicyHash ::= OCTET STRING SignPolicyInfo ::= SEQUENCE { signPolicyIdentifier SignPolicyId, dateOfIssue GeneralizedTime, policyIssuerName PolicyIssuerName, fieldOfApplication FieldOfApplication, signatureValidationPolicy SignatureValidationPolicy, signPolExtensions SignPolExtensions OPTIONAL } SignPolicyId ::= OBJECT IDENTIFIER PolicyIssuerName ::= GeneralNames FieldOfApplication ::= DirectoryString SignatureValidationPolicy ::= SEQUENCE { signingPeriod SigningPeriod, commonRules CommonRules, commitmentRules CommitmentRules, signPolExtensions SignPolExtensions OPTIONAL } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 77] Internet Draft Electronic Signature Formats SigningPeriod ::= SEQUENCE { notBefore GeneralizedTime, notAfter GeneralizedTime OPTIONAL } CommonRules ::= SEQUENCE { signerAndVeriferRules [0] SignerAndVerifierRules OPTIONAL, signingCertTrustCondition [1] SigningCertTrustCondition OPTIONAL, timeStampTrustCondition [2] TimestampTrustCondition OPTIONAL, attributeTrustCondition [3] AttributeTrustCondition OPTIONAL, algorithmConstraintSet [4] AlgorithmConstraintSet OPTIONAL, signPolExtensions [5] SignPolExtensions OPTIONAL } CommitmentRules ::= SEQUENCE OF CommitmentRule CommitmentRule ::= SEQUENCE { selCommitmentTypes SelectedCommitmentTypes, signerAndVeriferRules [0] SignerAndVerifierRules OPTIONAL, signingCertTrustCondition [1] SigningCertTrustCondition OPTIONAL, timeStampTrustCondition [2] TimestampTrustCondition OPTIONAL, attributeTrustCondition [3] AttributeTrustCondition OPTIONAL, algorithmConstraintSet [4] AlgorithmConstraintSet OPTIONAL, signPolExtensions [5] SignPolExtensions OPTIONAL } SelectedCommitmentTypes ::= SEQUENCE OF CHOICE { empty NULL, recognizedCommitmentType CommitmentType } CommitmentType ::= SEQUENCE { identifier CommitmentTypeIdentifier, fieldOfApplication [0] FieldOfApplication OPTIONAL, semantics [1] DirectoryString OPTIONAL } SignerAndVerifierRules ::= SEQUENCE { signerRules SignerRules, verifierRules VerifierRules } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 78] Internet Draft Electronic Signature Formats SignerRules ::= SEQUENCE { externalSignedData BOOLEAN OPTIONAL, -- True if signed data is external to CMS structure -- False if signed data part of CMS structure -- not present if either allowed mandatedSignedAttr CMSAttrs, -- Mandated CMS signed attributes mandatedUnsignedAttr CMSAttrs, -- Mandated CMS unsigned attributed mandatedCertificateRef [0] CertRefReq DEFAULT signerOnly, -- Mandated Certificate Reference mandatedCertificateInfo [1] CertInfoReq DEFAULT none, -- Mandated Certificate Info signPolExtensions [2] SignPolExtensions OPTIONAL } CMSAttrs ::= SEQUENCE OF OBJECT IDENTIFIER CertRefReq ::= ENUMERATED { signerOnly (1), -- Only reference to signer cert mandated fullPath (2) -- References for full cert path up to a trust -- point required } CertInfoReq ::= ENUMERATED { none (0) , -- No mandatory requirements signerOnly (1) , -- Only reference to signer cert mandated fullPath (2) -- References for full cert path up to a -- trust point mandated } VerifierRules ::= SEQUENCE { mandatedUnsignedAttr MandatedUnsignedAttr, signPolExtensions SignPolExtensions OPTIONAL } MandatedUnsignedAttr ::= CMSAttrs -- Mandated CMS unsigned attributed ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 79] Internet Draft Electronic Signature Formats CertificateTrustTrees ::= SEQUENCE OF CertificateTrustPoint CertificateTrustPoint ::= SEQUENCE { trustpoint Certificate, -- self-signed certificate pathLenConstraint [0] PathLenConstraint OPTIONAL, acceptablePolicySet [1] AcceptablePolicySet OPTIONAL, -- If not present "any policy" nameConstraints [2] NameConstraints OPTIONAL, policyConstraints [3] PolicyConstraints OPTIONAL } PathLenConstraint ::= INTEGER (0..MAX) AcceptablePolicySet ::= SEQUENCE OF CertPolicyId CertPolicyId ::= OBJECT IDENTIFIER NameConstraints ::= SEQUENCE { permittedSubtrees [0] GeneralSubtrees OPTIONAL, excludedSubtrees [1] GeneralSubtrees OPTIONAL } GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree GeneralSubtree ::= SEQUENCE { base GeneralName, minimum [0] BaseDistance DEFAULT 0, maximum [1] BaseDistance OPTIONAL } BaseDistance ::= INTEGER (0..MAX) PolicyConstraints ::= SEQUENCE { requireExplicitPolicy [0] SkipCerts OPTIONAL, inhibitPolicyMapping [1] SkipCerts OPTIONAL } SkipCerts ::= INTEGER (0..MAX) CertRevReq ::= SEQUENCE { endCertRevReq RevReq, caCerts [0] RevReq } RevReq ::= SEQUENCE { enuRevReq EnuRevReq, exRevReq SignPolExtensions OPTIONAL} ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 80] Internet Draft Electronic Signature Formats EnuRevReq ::= ENUMERATED { clrCheck (0), -- Checks must be made against current CRLs -- (or authority revocation lists) ocspCheck (1), -- The revocation status must be checked using -- the Online Certificate Status Protocol (RFC 2450) bothCheck (2), -- Both CRL and OCSP checks must be carried out eitherCheck (3), -- At least one of CRL or OCSP checks must be carried out noCheck (4), -- no check is mandated other (5) -- Other mechanism as defined by signature poilicy -- extension } SigningCertTrustCondition ::= SEQUENCE { signerTrustTrees CertificateTrustTrees, signerRevReq CertRevReq } TimestampTrustCondition ::= SEQUENCE { ttsCertificateTrustTrees [0] CertificateTrustTrees OPTIONAL, ttsRevReq [1] CertRevReq OPTIONAL, ttsNameConstraints [2] NameConstraints OPTIONAL, cautionPeriod [3] DeltaTime OPTIONAL, signatureTimestampDelay [4] DeltaTime OPTIONAL } DeltaTime ::= SEQUENCE { deltaSeconds INTEGER, deltaMinutes INTEGER, deltaHours INTEGER, deltaDays INTEGER } AttributeTrustCondition ::= SEQUENCE { attributeMandated BOOLEAN, -- Attribute must be present howCertAttribute HowCertAttribute, attrCertificateTrustTrees [0] CertificateTrustTrees OPTIONAL, attrRevReq [1] CertRevReq OPTIONAL, attributeConstraints [2] AttributeConstraints OPTIONAL } ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 81] Internet Draft Electronic Signature Formats HowCertAttribute ::= ENUMERATED { claimedAttribute (0), certifiedAttribtes (1), either (2) } AttributeConstraints ::= SEQUENCE { attributeTypeConstarints [0] AttributeTypeConstraints OPTIONAL, attributeValueConstarints [1] AttributeValueConstraints OPTIONAL } AttributeTypeConstraints ::= SEQUENCE OF AttributeType AttributeValueConstraints ::= SEQUENCE OF AttributeTypeAndValue AlgorithmConstraintSet ::= SEQUENCE { -- Algorithm constrains on: signerAlgorithmConstraints [0] AlgorithmConstraints OPTIONAL, -- signer eeCertAlgorithmConstraints [1] AlgorithmConstraints OPTIONAL, -- issuer of end entity certs. caCertAlgorithmConstraints [2] AlgorithmConstraints OPTIONAL, -- issuer of CA certificates aaCertAlgorithmConstraints [3] AlgorithmConstraints OPTIONAL, -- Attribute Authority tsaCertAlgorithmConstraints [4] AlgorithmConstraints OPTIONAL -- TimeStamping Authority } AlgorithmConstraints ::= SEQUENCE OF AlgAndLength AlgAndLength ::= SEQUENCE { algID OBJECT IDENTIFIER, minKeyLength INTEGER OPTIONAL, -- Minimum key length in bits other SignPolExtensions OPTIONAL } SignPolExtensions ::= SEQUENCE OF SignPolExtn SignPolExtn ::= SEQUENCE { extnID OBJECT IDENTIFIER, extnValue OCTET STRING } END -- ETS-ElectronicSignature-97Syntax ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 82] Internet Draft Electronic Signature Formats Annex B (informative): General Description This annex captures the concepts that apply to this document and the rational for the elements of the specification defined using ASN.1 in the main text of this document. The specification below includes a description why the component is needed, with a brief description of the vulnerabilities and threats and the manner by which they are countered. B.1 The Signature Policy The signature policy is a set of rules for the creation and validation of an electronic signature, under which the signature can be determined to be valid. A given legal/contractual context may recognize a particular signature policy as meeting its requirements. A signature policy may be issued, for example, by a party relying on the electronic signatures and selected by the signer for use with that relying party. Alternatively, a signature policy may be established through an electronic trading association for use amongst its members. Both the signer and verifier use the same signature policy. A signature policy has a globally unique reference, which is bound to an electronic signature by the signer as part of the signature calculation. The signature policy needs to be available in human readable form so that it can be assessed to meet the requirements of the legal and contractual context in which it is being applied. To facilitate the automatic processing of an electronic signature the parts of the signature policy which specify the electronic rules for the creation and validation of the electronic signature also needs to be in a computer processable form. The signature policy thus includes the following: * Rules, which apply to functionality, covered by this document (referred to as the Signature Validation Policy). * Rules which may be implied through adoption of Certificate Policies that apply to the electronic signature (e.g. rules for ensuring the secrecy of the private signing key). * Rules, which relate to the environment used by the signer, e.g. the use of an agreed CAD (Card Accepting Device) used in conjunction with a smart card. The Signature Validation Policy may be structured so that it can be computer processable. The current document includes, as an option, a formal structure for the signature validation policy based on the used of Abstract Syntax Notation 1 (ASN.1). Other formats of the signature validation policy are allowed by this document. However, for a given signature policy there must be one definitive form that has a unique binary encoded value. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 83] Internet Draft Electronic Signature Formats The Signature Validation Policy includes rules regarding use of TSPs (CA, Attribute Authorities, Time Stamping Authorities) as well as rules defining the components of the electronic signature that must be provided by the signer with data required by the verifier to provide long term proof. B.2 Signed Information The information being signed may be defined as a MIME-encapsulated message which can be used to signal the format of the content in order to select the right display or application. It can be composed of formatted text (e.g. EDIFACT), free text or of fields from an electronic form (e-form). For example, the Adobe(tm) format "pdf" may be used or the eXtensible Mark up Language (XML). B.3 Components of an Electronic Signature B.3.1 Reference to the Signature Policy The definition of electronic signature includes: "a commitment has been explicitly endorsed under a "Signature policy", at a given time, by a signer under an identifier, e.g. a name or a pseudonym, and optionally a role". When two independent parties want to evaluate an electronic signature, it is fundamental that they get the same result. To meet this requirement the technical components and technical aspects used in creating the signature must be referenced, this is provided by a reference to the "Signature Validation Policy". The "Signature Validation Policy" defines: * the components of an electronic signature to be provided by the signer; * any additional components (i.e. verifier components) used to validate an electronic signature at the time of receipt by a verifier and later by an arbitrator, auditor or other independent parties. By signing over the signature policy identifier, the algorithm identifier and the hash of the signature policy, the signer explicitly indicates that he or she has applied the signature policy in creating the signature. Thus, undertakes any commitments implied by the signature policy, any indication of commitment type included in the electronic signature, and the user data that is signed. The hash algorithm identifier and value is included to ensure that both the signer and verifier use exactly the same signature policy. This unambiguously binds the signer and verifier to same definitive form of the signature policy has a unique binary encoding. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 84] Internet Draft Electronic Signature Formats In order to identify unambiguously the "Signature Validation Policy" to be used to verify the signature an identifier and hash of the "Signature policy" must be part of the signed data. Additional information about the policy (e.g. web reference to the document) may be carried as "qualifiers" to the signature policy identifier B.3.2 Commitment Type Indication The definition of electronic signature includes: "a commitment has been explicitly endorsed under a signature policy, at a given time, by a signer under an identifier, e.g. a name or a pseudonym, and optionally a role". The commitment type can be indicated in the electronic signature either: * explicitly using a "commitment type indication" in the electronic signature; * implicitly or explicitly from the semantics of the signed data. If the indicated commitment type is explicit using a "commitment type indication" in the electronic signature , acceptance of a verified signature implies acceptance of the semantics of that commitment type. The semantics of explicit commitment types indications must be specified either as part of the signature policy or may be registered for generic use across multiple policies. If a signature includes a commitment type indication other than one of those recognized under the signature policy the signature must be treated as invalid. How commitment is indicated using the semantics of the data being signed is outside the scope of this document. NOTE: Examples of commitment indicated through the semantics of the data being signed, are: * An explicit commitment made by the signer indicated by the type of data being signed over. Thus, the data structure being signed can have an explicit commitment within the context of the application (e.g. EDIFACT purchase order). * An implicit commitment which is a commitment made by the signer because the data being signed over has specific semantics (meaning) which is only interpretable by humans, (i.e. free text). ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 85] Internet Draft Electronic Signature Formats B.3.4 Certificate Identifier from the Signer The definition of the ETSI electronic signature includes: "a commitment has been explicitly endorsed under a signature policy, at a given time, by a signer under an identifier, e.g. a name or a pseudonym, and optionally a role." In many real life environments users will be able to get from different CAs or even from the same CA, different certificates containing the same public key for different names. The prime advantage is that a user can use the same private key for different purposes. Multiple use of the private key is an advantage when a smart card is used to protect the private key, since the storage of a smart card is always limited. When several CAs are involved, each different certificate may contain a different identity, e.g. as a national or as an employee from a company. Thus when a private key is used for various purposes, the certificate is needed to clarify the context in which the private key was used when generating the signature. Where there is the possibility of multiple use of private keys it is necessary for the signer to indicate to the verifier the precise certificate to be used. Many current schemes simply add the certificate after the signed data and thus are subject to various substitution attacks. An example of a substitution attack is a "bad" CA that would issue a certificate to someone with the public key of someone else. If the certificate from the signer was simply appended to the signature and thus not protected by the signature, any one could substitute one certificate by another and the message would appear to be signed by some one else. In order to counter this kind of attack, the identifier of the signer has to be protected by the digital signature from the signer. Although it does not provide the same advantages as the previous technique, another technique to counter that threat has been identified. It requires all CAs to perform a Proof Of Possession of the private key at the time of registration. The problem with that technique is that it does not provide any guarantee at the time of verification and only some proof "after the event" may be obtained, if and only if the CA keeps the Proof Of Possession in audit trail. In order to identify unambiguously the certificate to be used for the verification of the signature an identifier of the certificate from the signer must be part of the signed data. B.3.5 Role Attributes The definition of electronic signature includes: "a commitment has been explicitly endorsed under a non repudiation security policy, at a given time, by a signer under an identifier, e.g. a name or a pseudonym, and optionally a role. " ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 86] Internet Draft Electronic Signature Formats While the name of the signer is important, the position of the signer within a company or an organization can be even more important. Some contracts may only be valid if signed by a user in a particular role, e.g. a Sales Director. In many cases whom the sales Director really is, is not that important but being sure that the signer is empowered by his company to be the Sales Director is fundamental. This document defines two different ways for providing this feature: * by placing a claimed role name in the CMS signed attributes field; * by placing a attribute certificate containing a certified role name in the CMS signed attributes field. NOTE: Another possible approach would have been to use additional attributes containing the roles name(s) in the signer's certificate. However, it was decided not to follow this approach as it breaks the basic philosophy of the certificate being issued for one primary purpose. Also, by using separate certificates for management of the signer's identity certificate and management of additional roles can simplify the management, as new identity keys need not be issued if a use of role is to be changed. B.3.5.1 Claimed Role The signer may be trusted to state his own role without any certificate to corroborate this claim. In which case the claimed role can be added to the signature as a signed attribute. B.3.5.2 Certified Role Unlike public key certificates that bind an identifier to a public key, Attribute Certificates bind the identifier of a certificate to some attributes, like a role. An Attribute Certificate is NOT issued by a CA but by an Attribute Authority (AA). The Attribute Authority will be most of the time under the control of an organization or a company that is best placed to know which attributes are relevant for which individual. The Attribute Authority may use or point to public key certificates issued by any CA, provided that the appropriate trust may be placed in that CA. Attribute Certificates may have various periods of validity. That period may be quite short, e.g. one day. While this requires that a new Attribute Certificate is obtained every day, valid for that day, this can be advantageous since revocation of such certificates may not be needed. When signing, the signer will have to specify which Attribute Certificate it selects. In order to do so, the Attribute Certificate will have to be included in the signed data in order to be protected by the digital signature from the signer. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 87] Internet Draft Electronic Signature Formats In order to identify unambiguously the attribute certificate(s) to be used for the verification of the signature an identifier of the attribute certificate(s) from the signer must be part of the signed data. B.3.6 Signer Location In some transactions the purported location of the signer at the time he or she applies his signature may need to be indicated. For this reason an optional location indicator must be able to be included. In order to provide indication of the location of the signer at the time he or she applied his signature a location attribute may be included in the signature. B.3.7 Signing Time The definition of electronic signature includes: "a commitment has been explicitly endorsed under a signature policy, at a given time, by a signer under an identifier, e.g. a name or a pseudonym, and optionally a role. " There are several ways to address this problem. The solution adopted in this document is to sign over a time which the signer claims is the signing time (i.e. claimed signing time) and to require a trusted time stamp to be obtained when building a ES with Timestamp. When a verifier accepts a signature, the two times must be within acceptable limits. The solution that is adopted in this document offers the major advantage that electronic signatures can be generated without any on- line connection to a trusted time source (i.e. they may be generated off-line). Thus two dates and two signatures are required: * a signing time indicated by the signer and which is part of the data signed by the signer (i.e. part of the basic electronic signature); * a time indicated by a TimeStamping Authority (TSA) which is signed over the digital signature value of the basic electronic signature. The signer, verifier or both may obtain the TSA timestamp. In order for an electronic signature to be valid under a signature policy, it must be timestamped by a TSA where the signing time as indicated by the signer and the time of time stamping as indicated by a TSA must be "close enough" to meet the requirements of the signature validation policy. "Close enough" means a few minutes, hours or even days according to the "Signature Validation Policy". ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 88] Internet Draft Electronic Signature Formats NOTE: The need for Timestamping is further explained in clause B.4.5. A further optional attribute is defined in this document to timestamp the content, to provide proof of the existence of the content, at the time indicated by the timestamp. Using this optional attribute a trusted secure time may be obtained before the document is signed and included under the digital signature. This solution requires an on-line connection to a trusted timestamping service before generating the signature and may not represent the precise signing time, since it can be obtained in advance. However, this optional attribute may be used by the signer to prove that the signed object existed before the date included in the timestamp (see 4.12.3, Content Timestamp). Also, the signing time should be between the time indicated by this timestamp and time indicated by the ES-T timestamp. B.4 Components of Validation Data B.4.1 Revocation Status Information A verifier will have to prove that the certificate of the signer was valid at the time of the signature. This can be done by either: * using Certificate Revocation Lists (CRLs); * using responses from an on-line certificate status server (for example; obtained through the OCSP protocol). B.4.2 CRL Information When using CRLs to get revocation information, a verifier will have to make sure that he or she gets at the time of the first verification the appropriate certificate revocation information from the signer's CA. This should be done as soon as possible to minimize the time delay between the generation and verification of the signature. This involves checking that the signer certificate serial number is not included in the CRL. The signer, the verifier or any other third party may obtain either this CRL. If obtained by the signer, then it must be conveyed to the verifier. It may be convenient to archive the CRL for ease of subsequent verification or arbitration. Alternatively, provided the CRL is archived elsewhere which is accessible for the purpose of arbitration, then the serial number of the CRL used may be archived together with the verified electronic signature. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 89] Internet Draft Electronic Signature Formats It may happen that the certificate serial number appears in the CRL but with the status "suspended" (i.e. on hold). In such a case, the electronic signature is not yet valid, since it is not possible to know whether the certificate will or will not be revoked at the end of the suspension period. If a decision has to be taken immediately then the signature has to be considered as invalid. If a decision can wait until the end of the suspension period, then two cases are possible: * the certificate serial number has disappeared from the list and thus the certificate can be considered as valid and that CRL must be captured and archived either by the verifier or elsewhere and be kept accessible for the purpose of arbitration. * the certificate serial number has been maintained on the list with the status definitively revoked and thus the electronic signature must be considered as invalid and discarded. At this point the verifier may be convinced that he or she got a valid signature, but is not yet in a position to prove at a later time that the signature was verified as valid. Before addressing this point, an alternative to CRL is to use OCSP responses. B.4.3 OCSP Information When using OCSP to get revocation information , a verifier will have to make sure that he or she gets at the time of the first verification an OCSP response that contains the status "valid". This should be done as soon as possible after the generation of the signature. The signer, the verifier or any other third party may fetch this OCSP response. Since OSCP responses are transient and thus are not archived by any TSP including CA, it is the responsibility of every verifier to make sure that it is stored in a safe place. The simplest way is to store them associated with the electronic signature. An alternative would be to store them in some storage so that they can then be easily retrieved. In the same way as for the case of the CRL, it may happen that the certificate is declared as invalid but with the secondary status "suspended". In such a case, the electronic signature is not yet valid, since it is not possible to know whether the certificate will or will not be revoked at the end of the suspension period. If a decision has to be taken immediately then the electronic signature has to be considered as invalid. If a decision can wait until the end of the suspension period, then two cases are possible: * An OCSP response with a valid status is obtained at a later date and thus the certificate can be considered as valid and that OCSP response must be captured. * An OCSP response with an invalid status is obtained with a secondary status indicating that the certificate is definitively revoked and thus the electronic signature must be considered as invalid and discarded. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 90] Internet Draft Electronic Signature Formats As in the CRL case, at this point, the verifier may be convinced that he or she got a valid signature, but is not yet in a position to prove at a later time that the signature was verified as valid. B.4.4 Certification Path A verifier will have to prove that the certification path was valid, at the time of the signature, up to a trust point according to the naming constraints and the certificate policy constraints from the "Signature Validation Policy". It will be necessary to capture all the certificates from the certification path, starting with those from the signer and ending up with those of the self-signed certificate from one trusted root of the "Signature Validation Policy". In addition, it will be necessary to capture the Authority Revocation Lists (ARLs) to prove than none of the CAs from the chain was revoked at the time of the signature. As in the OCSP case, at this point, the verifier may be convinced that he or she got a valid signature, but is not yet in a position to prove at a later time that the signature was verified as valid. B.4.5 Timestamping for Long Life of Signature An important property for long standing signatures is that a signature, having been found once to be valid, must continue to be so months or years later. A signer, verifier or both may be required to provide on request, proof that a digital signature was created or verified during the validity period of the all the certificates that make up the certificate path. In this case, the signer, verifier or both will also be required to provide proof that all the user and CA certificates used were not revoked when the signature was created or verified. It would be quite unacceptable, to consider a signature as invalid even if the keys or certificates were later compromised. Thus there is a need to be able to demonstrate that the signature keys was valid around the time that the signature was created to provide long term evidence of the validity of a signature. It could be the case that a certificate was valid at the time of the signature but revoked some time later. In this event, evidence must be provided that the document was signed before the signing key was revoked. Timestamping by a Time Stamping Authority (TSA) can provide such evidence. A time stamp is obtained by sending the hash value of the given data to the TSA. The returned "timestamp" is a signed document that contains the hash value, the identity of the TSA, and the time of stamping. This proves that the given data existed before the time of stamping. Timestamping a digital signature (by sending a hash of the signature to the TSA) before the revocation of the signer's private key, provides evidence that the signature has been created before the key was revoked. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 91] Internet Draft Electronic Signature Formats If a recipient wants to hold a valid electronic signature he will have to ensure that he has obtained a valid time stamp for it, before that key (and any key involved in the validation) is revoked. The sooner the timestamp is obtained after the signing time, the better. It is important to note that signatures may be generated "off-line" and time-stamped at a later time by anyone, for example by the signer or any recipient interested in the value of the signature. The time stamp can thus be provided by the signer together with the signed document, or obtained by the recipient following receipt of the signed document. The time stamp is NOT a component of the Electronic Signature, but the essential component of the ES with Timestamp. It is required in this document that signer's digital signature value is timestamped by a trusted source, known as a TimeStamping Authority. This document requires that the signer's digital signature value is timestamped by a trusted source before the electronic signature can become a ES with Complete validation data (ES-C). The acceptable TSAs are specified in the Signature Validation Policy. Should both the signer and verifier be required to timestamp the signature value to meet the requirements of the signature policy, the signature policy MAY specify a permitted time delay between the two time stamps. B.4.6 Timestamping for Long Life of Signature before CA Key Compromises Timestamped extended electronic signatures are needed when there is a requirement to safeguard against the possibility of a CA key in the certificate chain ever being compromised. A verifier may be required to provide on request, proof that the certification path and the revocation information used a the time of the signature were valid, even in the case where one of the issuing keys or OCSP responder keys is later compromised. The current document defines two ways of using timestamps to protect against this compromise: * Timestamp the ES with Complete validation data, when an OCSP response is used to get the status of the certificate from the signer. * Timestamp only the certification path and revocation information references when a CRL is used to get the status of the certificate from the signer. NOTE: the signer, verifier or both may obtain the timestamp. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 92] Internet Draft Electronic Signature Formats B.4.6.1 Timestamping the ES with Complete validation data When an OCSP response is used, it is necessary to time stamp in particular that response in the case the key from the responder would be compromised. Since the information contained in the OCSP response is user specific and time specific, an individual time stamp is needed for every signature received. Instead of placing the time stamp only over the certification path references and the revocation information references, which include the OCSP response, the time stamp is placed on the ES-C. Since the certification path and revocation information references are included in the ES with Complete validation data they are also protected. For the same cryptographic price, this provides an integrity mechanism over the ES with Complete validation data. Any modification can be immediately detected. It should be noticed that other means of protecting/detecting the integrity of the ES with Complete Validation Data exist and could be used. Although the technique requires a time stamp for every signature, it is well suited for individual users wishing to have an integrity protected copy of all the validated signatures they have received. By timestamping the complete electronic signature, including the digital signature as well as the references to the certificates and revocation status information used to support validation of that signature, the timestamp ensures that there is no ambiguity in the means of validating that signature. This technique is referred to as ES with eXtended validation data (ES- X), type 1 Timestamped in this document. NOTE: Trust is achieved in the references by including a hash of the data being referenced. If it is desired for any reason to keep a copy of the additional data being referenced, the additional data may be attached to the electronic signature, in which case the electronic signature becomes a ES-X Long as defined by this document. A ES-X Long Timestamped is simply the concatenation of a ES-X Timestamped with a copy of the additional data being referenced. B.4.6.2 Timestamping Certificates and Revocation Information References Timestamping each ES with Complete validation data as defined above may not be efficient, particularly when the same set of CA certificates and CRL information is used to validate many signatures. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 93] Internet Draft Electronic Signature Formats Timestamping CA certificates will stop any attacker from issuing bogus CA certificates that could be claimed to existing before the CA key was compromised. Any bogus timestamped CA certificates will show that the certificate was created after the legitimate CA key was compromised. In the same way, timestamping CA CRLs, will stop any attacker from issuing bogus CA CRLs which could be claimed to existing before the CA key was compromised. Timestamping of commonly used certificates and CRLs can be done centrally, e.g. inside a company or by a service provider. This method reduces the amount of data the verifier has to timestamp, for example it could reduce to just one time stamp per day (i.e. in the case were all the signers use the same CA and the CRL applies for the whole day). The information that needs to be time stamped is not the actual certificates and CRLs but the unambiguous references to those certificates and CRLs. To comply with extended validation data, type 2 Timestamped, this document requires the following: * All the CA certificates references and revocation information references (i.e. CRLs) used in validating the ES-C are covered by one or more timestamp. Thus a ES-C with a timestamp signature value at time T1, can be proved valid if all the CA and CRL references are timestamped at time T1+. B.4.7 Timestamping for Long Life of Signature Advances in computing increase the probability of being able to break algorithms and compromise keys. There is therefore a requirement to be able to protect electronic signatures against this probability. Over a period of time weaknesses may occur in the cryptographic algorithms used to create an electronic signature (e.g. due to the time available for cryptoanalysis, or improvements in cryptoanalytical techniques). Before this such weaknesses become likely, a verifier should take extra measures to maintain the validity of the electronic signature. Several techniques could be used to achieve this goal depending on the nature of the weakened cryptography. In order to simplify, a single technique, called Archive validation data, covering all the cases is being used in this document. Archive validation data consists of the Complete validation data and the complete certificate and revocation data, time stamped together with the electronic signature. The Archive validation data is necessary if the hash function and the crypto algorithms that were used to create the signature are no longer secure. Also, if it cannot be assumed that the hash function used by the Time Stamping Authority is secure, then nested timestamps of Archived Electronic Signature are required. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 94] Internet Draft Electronic Signature Formats The potential for Trusted Service Provider (TSP) key compromise should be significantly lower than user keys, because TSP(s) are expected to use stronger cryptography and better key protection. It can be expected that new algorithms (or old ones with greater key lengths) will be used. In such a case, a sequence of timestamps will protect against forgery. Each timestamp needs to be affixed before either the compromise of the signing key or of the cracking of the algorithms used by the TSA. TSAs (TimeStamping Authorities) should have long keys (e.g. which at the time of drafting this document was 2048 bits for the signing RSA algorithm) and/or a "good" or different algorithm. Nested timestamps will also protect the verifier against key compromise or cracking the algorithm on the old electronic signatures. The process will need to be performed and iterated before the cryptographic algorithms used for generating the previous time stamp are no longer secure. Archive validation data may thus bear multiple embedded time stamps. B.4.8 Reference to Additional Data Using type 1 or 2 of Timestamped extended validation data verifiers still needs to keep track of all the components that were used to validate the signature, in order to be able to retrieve them again later on. These components may be archived by an external source like a trusted service provider, in which case referenced information that is provided as part of the ES with Complete validation data (ES-C) is adequate. The actual certificates and CRL information reference in the ES-C can be gathered when needed for arbitration. B.4.9 Timestamping for Mutual Recognition In some business scenarios both the signer and the verifier need to timestamp their own copy of the signature value. Ideally the two timestamps should be as close as possible to each other. Example: A contract is signed by two parties A and B representing their respective organizations, to timestamp the signer and verifier data two approaches are possible: * under the terms of the contract pre-defined common "trusted" TSA may be used; * if both organizations run their own timestamping services, A and B can have the transaction timestamped by these two timestamping services.In the latter case, the electronic signature will only be considered as valid, if both timestamps were obtained in due time (i.e. there should not be a long delay between obtaining the two timestamps). Thus, neither A nor B can repudiate the signing time indicated by their own timestamping service. Therefore, A and B do not need to agree on a common "trusted" TSA to get a valid transaction. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 95] Internet Draft Electronic Signature Formats It is important to note that signatures may be generated "off-line" and timestamped at a later time by anyone, e.g. by the signer or any recipient interested in validating the signature. The timestamp over the signature from the signer can thus be provided by the signer together with the signed document, and /or obtained by the verifier following receipt of the signed document. The business scenarios may thus dictate that one or more of the long- term signature timestamping methods describe above be used. This will need to be part of a mutually agreed the Signature Validation Policy with is part of the overall signature policy under which digital signature may be used to support the business relationship between the two parties. B.4.10 TSA Key Compromise TSA servers should be built in such a way that once the private signature key is installed, that there is minimal likelihood of compromise over as long as possible period. Thus the validity period for the TSA's keys should be as long as possible. Both the ES-T and the ES-C contain at least one time stamp over the signer's signature. In order to protect against the compromise of the private signature key used to produce that timestamp, the Archive validation data can be used when a different TimeStamping Authority key is involved to produce the additional timestamp. If it is believed that the TSA key used in providing an earlier timestamp may ever be compromised (e.g. outside its validity period), then the ES-A should be used. For extremely long periods this may be applied repeatedly using new TSA keys. B.5 Multiple Signatures Some electronic signatures may only be valid if they bear more than one signature. This is the case generally when a contract is signed between two parties. The ordering of the signatures may or may not be important, i.e. one may or may not need to be applied before the other. Several forms of multiple and counter signatures need to be supported, which fall into two basic categories: * independent signatures; * embedded signatures. Independent signatures are parallel signatures where the ordering of the signatures is not important. The capability to have more than one independent signature over the same data must be provided. Embedded signatures are applied one after the other and are used where the order the signatures are applied is important. The capability to sign over signed data must be provided. These forms are described in clause 4.13. All other multiple signature schemes, e.g. a signed document with a countersignature, double countersignatures or multiple signatures, can be reduced to one or more occurrence of the above two cases. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 96] Internet Draft Electronic Signature Formats Annex C (informative): C.1 Signature Policy and Signature Validation Policy The definition of electronic signature mentions: "a commitment has been explicitly endorsed under a "Signature Policy", at a given time, by a signer under an identifier, e.g. a name or a pseudonym, and optionally a role. " Electronic signatures are commonly applied within the context of a legal or contractual framework. This establishes the requirements on the electronic signatures and any special semantics (e.g. agreement, intent). These requirements may be defined in very general abstract terms or in terms of detailed rules. The specific semantics associated with an electronic signature implied by a legal or contractual framework are outside the scope of this document. If the signature policy is recognized, within the legal/contractual context, as providing commitment, then the signer explicitly agrees with terms and conditions which are implicitly or explicitly part of the signed data. When two independent parties want to evaluate an electronic signature, it is fundamental that they get the same result. It is therefore important that the conditions agreed by the signer at the time of signing are indicated to the verifier and any arbitrator. An aspect that enables this to be known by all parties is the signature policy. The technical implications of the signature policy on the electronic signature with all the validation data are called the "Signature Validation Policy". The signature validation policy specifies the rules used to validate the signature. This document does not mandate the form and encoding of the specification of the signature policy. However, for a given signature policy there must be one definitive form that has a unique binary encoded value. This document includes, as an option, a formal structure for signature validation policy based on the use of Abstract Syntax Notation 1 (ASN.1). Given the specification of the signature policy and its hash value an implementation of a verification process must obey the rules defined in the specification. This document places no restriction on how it should be implemented. Provide the implementation conforms to the conformance requirements as define in clause 14.1, 14.2 and 14.3 implementation options include: ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 97] Internet Draft Electronic Signature Formats A validation process that supports a specific signature policy as identified by the signature policy OID. Such an implementation should conform to a human readable description provided all the processing rules of the signature policy are clearly defined. However, if additional policies need to be supported, then such an implementation would need to be customized for each additional policy. This type of implementation may be simpler to implement initially, but can be difficult to enhance to support numerous additional signature policies. A validation process that is dynamically programmable and able to adapt its validation rules in accordance with a description of the signature policy provided in a computer-processable language. This present document defines such a policy using an ASN.1 structure (see 6.1). This type of implementation could support multiple signature policies without being modified every time, provided all the validation rules specified as part of the signature policy are known by the implementation. (i.e. only requires modification if there are additional rules specified). The precise content of a signature policy is not mandated by the current document. However, a signature policy must be sufficiently definitive to avoid any ambiguity as to its implementation requirements. It must be absolutely clear under which conditions an electronic signature should be accepted. For this reason, it should contain the following information: * General information about the signature policy which includes: - a unique identifier of the policy; - the name of the issuer of the policy; - the date the policy was issued; - the field of application of the policy. * The signature verification policy which includes: - the signing period, - a list of recognized commitment types; - rules for Use of Certification Authorities; - rules for Use of Revocation Status Information; - rules for Use of Roles; - rules for use of Timestamping and Timing; - signature verification data to be provided by the signer/collected by verifier; - any constraints on signature algorithms and key lengths. * Other signature policy rules required to meet the objectives of the signature. Variations of the validation policy rules may apply to different commitment types. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 98] Internet Draft Electronic Signature Formats C.2 Identification of Signature Policy When data is signed the signer indicates the signature policy applicable to that electronic signature by including an object identifier for the signature policy with the signature. The signer and verifier must apply the rules specified by the identified policy. In addition to the identifier of the signature policy the signer must include the hash of the signature policy, so it can be verified that the policy selected by the signer is the identical to the one being used the verifier. A signature policy may be qualified by additional information. This can includes: * A URL where a copy of the Signature Policy may be obtained; * A user notice that should be displayed when the signature is verified; If no signature policy is identified then the signature may be assumed to have been generated/verified without any policy constraints, and hence may be given no specific legal or contractual significance through the context of a signature policy. A "Signature Policy" will be identifiable by an OID (Object Identifier) and verifiable using a hash of the signature policy. C.3 General Signature Policy Information General information should be recorded about the signature policy along with the definition of the rules which form the signature policy as described in subsequent subclauses. This should include: * Policy Object Identifier: The "Signature Policy" will be identifiable by an OID (Object Identifier) whose last component (i.e. right most) is an integer that is specific to a particular version issued on the given date. * Date of issue: When the "Signature Policy" was issued. * Signature Policy Issuer name: An identifier for the body responsible for issuing the Signature Policy. This may be used by the signer or verifying in deciding if a policy is to be trusted, in which case the signer/verifier must authenticate the origin of the signature policy as coming from the identified issuer. * Signing period: The start time and date, optionally with an end time and date, for the period over which the signature policy may be used to generate electronic signatures. * Field of application: This defines in general terms the general legal/contract/application contexts in which the signature policy is to be used and the specific purposes for which the electronic signature is to be applied. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 99] Internet Draft Electronic Signature Formats C.4 Recognized Commitment Types The signature validation policy may recognize one or more types of commitment as being supported by electronic signatures produced under the security policy.If an electronic signature does not contain a recognized commitment type then the semantics of the electronic signature is dependent on the data being signed and the context in which it is being used. Only recognized commitment types are allowed in an electronic signature. The definition of a commitment type includes: * the object identifier for the commitment; * the contractual/legal/application context in which the signature may be used (e.g. submission of messages); * a description of the support provided within the terms of the context (e.g. proof that the identified source submitted the message if the signature is created when message submission is initiated). The definition of a commitment type can be registered: * as part of the validation policy; * as part of the application/contract/legal environment; * as part of generic register of definitions. The legal/contractual context will determine the rules applied to the signature, as defined by the signature policy and its recognized commitment types, make it fit for purpose intended. C.5 Rules for Use of Certification Authorities The certificate validation process of the verifier, and hence the certificates that may be used by the signer for a valid electronic signature, may be constrained by the combination of the trust point and certificate path constraints in the signature validation policy. C.5.1 Trust Points The signature validation policy defines the certification authority trust points that are to be used for signature verification. Several trust points may be specified under one signature policy. Specific trust points may be specified for a particular type of commitment defined under the signature policy. For a signature to be valid a certification path must exists between the Certification Authority that has granted the certificate selected by the signer (i.e. the used user-certificate) and one of the trust point of the "Signature Validation Policy". ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 100] Internet Draft Electronic Signature Formats C.5.2 Certification Path There may be constraints on the use of certificates issued by one or more CA(s) in the certificate chain and trust points. The two prime constraints are certificate policy constraints and naming constraints: * Certificate policy constraints limit the certification chain between the user certificate and the certificate of the trusted point to a given set of certificate policies, or equivalents identified through certificate policy mapping. * The naming constraints limit the forms of names that the CA is allowed to certify. Name constraints are particularly important when a "Signature policy" identifies more than one trust point. In this case, a certificate of a particular trusted point may only be used to verify signatures from users with names permitted under the name constraint. Certificate Authorities may be organized in a tree structure, this tree structure may represent the trust relationship between various CA(s) and the users CA. Alternatively, a mesh relationship may exist where a combination of tree and peer cross-certificates may be used. The requirement of the certificate path in this document is that it provides the trust relationship between all the CAs and the signers user certificate. The starting point from a verification point of view, is the "trust point". A trust point is usually a CA that publishes self-certified certificates, is the starting point from which the verifier verifies the certificate chain. Naming constraints may apply from the trust point, in which case they apply throughout the set of certificates that make up the certificate path down to the signer's user certificate. Policy constraints can be easier to process but to be effective require the presence of a certificate policy identifier in the certificates used in a certification path. Certificate path processing, thus generally starts with one of the trust point from the signature policy and ends with the user certificate. The certificate path processing procedures defined in RFC 2459 clause 6 identifies the following initial parameters that are selected by the verifier in certificate path processing: * acceptable certificate policies; * naming constraints in terms of constrained and excluded naming subtree; * requirements for explicit certificate policy indication and whether certificate policy mapping are allowed; * restrictions on the certificate path length. The signature validation policy identifies constraints on these parameters. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 101] Internet Draft Electronic Signature Formats C.5 Revocation Rules The signature policy should defines rules specifying requirements for the use of certificate revocation lists (CRLs) and/or on-line certificate status check service to check the validity of a certificate. These rules specify the mandated minimum checks that must be carried out. It is expected that in many cases either check may be selected with CRLs checks being carried out for certificate status that are unavailable from OCSP servers. The verifier may take into account information in the certificate in deciding how best to check the revocation status (e.g. a certificate extension field about authority information access or a CRL distribution point) provided that it does not conflict with the signature policy revocation rules. C.6 Rules for the Use of Roles Roles can be supported as claimed roles or as certified roles using Attribute Certificates. C.6.1 Attribute Values When signature under a role is mandated by the signature policy, then either Attribute Certificates may be used or the signer may provide a claimed role attribute. The acceptable attribute types or values may be dependent on the type of commitment. For example, a user may have several roles that allow the user to sign data that imply commitments based on one or more of his roles. C.6.2 Trust Points for Certified Attributes When a signature under a certified role is mandated by the signature policy, Attribute Authorities are used and need to be validated as part of the overall validation of the electronic signature. The trust points for Attribute Authorities do not need to be the same as the trust points to evaluate a certificate from the CA of the signer. Thus the trust point for verifying roles need not be the same as trust point used to validate the certificate path of the user's key. Naming and certification policy constraints may apply to the AA in similar circumstance to when they apply to CA. Constraints on the AA and CA need not be exactly the same. AA(s) may be used when a signer is creating a signature on behalf of an organization, they can be particularly useful when the signature represents an organizational role. AA(s) may or may not be the same authority as CA(s). Thus, the Signature Policy identifies trust points that can be used for Attribute Authorities, either by reference to the same trust points as used for Certification Authorities, or by an independent list. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 102] Internet Draft Electronic Signature Formats C.6.3 Certification Path for Certified Attributes Attribute Authorities may be organized in a tree structure in similar way to CA where the AAs are the leafs of such a tree. Naming and other constraints may be required on attribute certificate paths in a similar manner to other electronic signature certificate paths. Thus, the Signature Policy identify constraints on the following parameters used as input to the certificate path processing: * acceptable certificate policies, including requirements for explicit certificate policy indication and whether certificate policy mapping is allowed; * naming constraints in terms of constrained and excluded naming subtrees; * restrictions on the certificate path length. C.7 Rules for the Use of Timestamping and Timing The following rules should be used when specifying, constraints on the certificate paths for timestamping authorities, constraints on the timestamping authority names and general timing constraints. C.7.1 Trust Points and Certificate Paths Signature keys from timestamping authorities will need to be supported by a certification path. The certification path used for timestamping authorities requires a trustpoint and possibly path constraints in the same way that the certificate path for the signer's key. C.7.2 Timestamping Authority Names Restrictions may need to be placed by the validation policy on the named entities that may act a timestamping authorities. C.7.3 Timing Constraints - Caution Period Before an electronic signature may really be valid, the verifier has to be sure that the holder of the private key was really the only one in possession of key at the time of signing. However, there is an inevitable delay between a compromise or loss of key being noted, and a report of revocation being distributed. To allow greater confidence in the validity of a signature, a "cautionary period" may be identified before a signature may be said to be valid with high confidence. A verifier may revalidate a signature after this cautionary signature, or wait for this period before validating a signature. The validation policy may specify such a cautionary period. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 103] Internet Draft Electronic Signature Formats C.7.4 Timing Constraints - Timestamp Delay There will be some delay between the time that a signature is created and the time the signer's digital signature is timestamped. However, the longer this elapsed period the greater the risk of the signature being invalidated due to compromise or deliberate revocation of its private signing key by the signer. Thus the signature policy should specify a maximum acceptable delay between the signing time as claimed by the signer and the time included within the timestamp. C.8 Rules for Verification Data to be followed By specifying the requirements on the signer and verifier the responsibilities of the two parties can be clearly defined to establish all the necessary information. These verification data rules should include: * requirements on the signer to provide given signed attributes; * requirements on the verifier to obtain additional certificates, CRLs, results of on line certificate status checks and to use timestamps (if no already provided by the signer). C.9 Rules for Algorithm Constraints and Key Lengths The signature validation policy may identify a set of signing algorithms (hashing, public key, combinations) and minimum key lengths that may be used: * by the signer in creating the signature; * in end entity public key Certificates; * CA Certificates; * attribute Certificates; * by the timestamping authority. C.10 Other Signature Policy Rules The signature policy may specify additional policy rules, for example rules that relate to the environment used by the signer. These additional rules may be defined in computer processable and/or human readable form. C.11 Signature Policy Protection When signer or verifier obtains a copy of the Signature Policy from an issuer, the source should be authenticated (for example by using electronic signatures). When the signer references a signature policy the Object Identifier (OID) of the policy, the hash value and the hash algorithm OID of that policy must be included in the Electronic Signature. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 104] Internet Draft Electronic Signature Formats It is a mandatory requirement of this present document that the signature policy value computes to one, and only one hash value using the specified hash algorithm. This means that there must be a single binary value of the encoded form of the signature policy for the unique hash value to be calculated. For example, there may exist a particular file type, length and format on which the hash value is calculated which is fixed and definitive for a particular signature policy. The hash value may be obtained by: the signer performing his own computation of the hash over the signature policy using his preferred hash algorithm permitted by the signature policy, and the definitive binary encoded form. the signer, having verified the source of the policy, may use both the hash algorithm and the hash value included in the computer processable form of the policy (see section 6.1). ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 105] Internet Draft Electronic Signature Formats Annex D (informative): Identifiers and roles D.1 Signer Name Forms The name used by the signer, held as the subject in the signer's certificate, must uniquely identify the entity. The name must be allocated and verified on registration with the Certification Authority, either directly or indirectly through a Registration Authority, before being issued with a Certificate. This document places no restrictions on the form of the name. The subject's name may be a distinguished name, as defined in ITU-T Recommendation X.500 [15], held in the subject field of the certificate, or any other name form held in the X.509 subjectAltName certificate extension field. In the case that the subject has no distinguished name, the subject name can be an empty sequence and the subjectAltName extension must be critical. D.2 TSP Name Forms All TSP name forms (Certification Authorities, Attribute Authorities and TimeStamping Authorities) must be in the form of a distinguished name held in the subject field of the certificate. The TSP name form must include identifiers for the organization providing the service and the legal jurisdiction (e.g. country) under which it operates. D.3 Roles and Signer Attributes Where a signer signs as an individual but wishes to also identify him/herself as acting on behalf of an organization, it may be necessary to provide two independent forms of identification. The first identity, with is directly associated with the signing key identifies him/her as an individual. The second, which is managed independently, identifies that person acting as part of the organization, possibly with a given role. In this case the first identity is carried in the subject/subjectAltName field of the signer's certificate as described above. This document supports the following means of providing a second form of identification: * by placing a secondary name field containing a claimed role in the CMS signed attributes field; * by placing an attribute certificate containing a certified role in the CMS signed attributes field. ETSI TC-SEC, Ross, Pinkas, Pope Informational RFC [Page 106]