Internet Draft Adams, Sylvester, Zolotarev, Zuccherato PKIX Working Group October 12, 1999 expires April 12, 2000 Internet X.509 Public Key Infrastructure Data Validation and Certification Server Protocols Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 This document describes a general data validation and certification service and the protocols to be used when communicating with it. The Data Validation and Certification Server is a Trusted Third Party (TTP) that can be used as one component in building reliable non- repudiation services (see [ISONR]). Useful Data Validation and Certification Server responsibilities in a PKI are to validate signed documents and to assert the validity of public key certificates at a given time. We give examples of how to use the Data Certification Server to extend the lifetime of a signature beyond key expiry or revocation and to query the Data Certification Server regarding the status of a public key certificate. Note: The initial drafts of this protocol used the abbreviation DCS instead of DVCS. Adams, Sylvester, Zolotarev, Zuccherato [Page 1] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 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]. A complete list of ASN.1 will be added in an appendix. 1. Introduction A Data Validation Server (DVCS) is a Trusted Third Party (TTP) providing data validation services, asserting correctness of digitally signed documents, validity of public key certificates, and possession of data. As a result of the assertion, a DVCS generates a Data Validation Certificate (DVC) The data validation certificate can be used for constructing evidence of non-repudiation, relating to the validity and correctness of an entity's claim to possess data, the validity and revocation status of an entity's public key certificate and the validity and correctness of a digitally signed document. DVCS services do not replace the usage of CRLs and OCSP for public key certificate revocation checking in large open environments, due to concerns about the scalability of this protocol. It should be rather used to support non-repudiation or to supplement more traditional services concerning paperless document environments. The presence of a data validation certificate supports non-repudiation in two ways. It provides evidence that a digitally signed document or public key certificate was valid at the time indicated in the dvc. The dvc for a public key certificate can be used even after the public key certificate expires and its revocation information is no longer or not easily available; it is assumed that verifying the validity of a dvc is easier, since the population is smaller. The production of a data validation certificate in response to a signed request for validation of a signed document or public key certificate also provides evidence that due diligence was performed by the requester in validating a digital signature or public key certificate. 2. DVCS Services The current specification defines 4 types of validation and certification services: - Certification of Possession of Data (cpd), - Certification of Claim of Possession of Data (ccpd), - Validation of Digitally Signed Document (vsd), and - Validation of Public Key Certificates (vpkc). Adams, Sylvester, Zolotarev, Zuccherato [Page 2] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 A DVCS is REQUIRED to support at least a subset of these services. On completion of each service, the DVCS produces a data validation certificate - a signed document containing the validation results and trustworthy time information. 2.1 Certifying Possession of Data The Certify Possession of Data service provides evidence that the requester possessed data at the time indicated and that the actual data where presented to the Data Validation Server. 2.2 Certification of Claim of possession of Data The Certify Claim of Possession service is similar to the previous one, except that the requester does not present the data itself but a message digest. This service is similar to time stamping services as described in [TSP]. 2.3 Validation of Digitally Signed Documents The Validation of Digitally Signed Document service is used when validity of a signed document is to be asserted. The DVCS verifies all signatures the signed document using all appropriate status information and public key certificates. The DVCS verifies the mathematical correctness of all signatures attached to the document and also checks whether the signing entities can be trusted, for example by validating the full certification path from the signing entities to a trusted point (e.g., the DVCS's CA, or the root CA in a hierarchy). The DVCS MAY be able to rely on relevant CRLs or MAY need to supplement this with access to more current status information from the CAs for example by accessing to an OCSP service, a trusted directory service, or other DVS services. The DVCS will perform verification of all signatures attached to the signed document. A failure of the verification of one of the signatures does not necessarily result in the failure of the entire certification, and vice versa, a global failure may occur if the document has an insufficient number of signatures. 2.4 Certifying Public Key Certificate The Certify Public Key Certificate service is used to verify the validity (according to [RFC2459]) of one or more public key certificates at the specified time. Adams, Sylvester, Zolotarev, Zuccherato [Page 3] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 When certifying a public key certificate, the DVS verifies that the certificate included in the request is a valid certificate and determines its revocation status at a specified time. DVS checks the full certification path from the certificate's issuer to a trusted point. Again the DVCS MAY be able to rely on external information (CRL, OCSP, DVCS). 3. Data Certification Server usage and scenarios. It is outside the scope of this document to completely describe different operational scenarios, or usages for DVCS. See Appendix B and C for a set of examples and use cases. The Validate Signed Document service can be used to support non- repudiation services, to allow use of the signed document beyond public key certificate revocation or expiry, or simply to delegate signature validation to a trusted central (company wide) service. The Validate Public Key Certificate service can be used when timely information regarding a certificate's revocation status is required (e.g. high value funds transfer or the compromise of a highly sensitive key) or when evidence supporting non-repudiation is required. A data validation certificate may be used to simplify the validation of a signature beyond the expiry or subsequent revocation of the signing certificate: a Data validation certificate used as an authenticated attribute in a signature includes an additional assertion about the usability of a certificate that was used for signing. In order to validate such a signature it may be sufficient to only validate the data validation certificate. A data validation certificate for a key exchange certificate may contain additional certificates to be used as a simple method to indicate to a client to encrypt a session key for additional authorised entities (e.g., to support company wide recovery). The Certify Claim of Possession of Data is equivalent to the services described in [TSP]. The Certify Possession of data service can be used to assert legal deposit of documents, or to implement archival services as a trusted third party service. The Data Validation and Certification Server Protocols can be used in different service contexts. Examples include company-wide centralised services (verification of signatures, certification of company Adams, Sylvester, Zolotarev, Zuccherato [Page 4] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 certificates), service to cooperate in a multi-organisation community, or general third party services for time stamping or data archival. An important application of DVCS is an enterprise environment where all security decision are based on company wide rules. A company wide DVCS service can be used to delegate all technical decisions (e.g., path validation, trust configuration) to a centrally managed service. In all cases, the trust that PKI entities have in the Data Validation and Certification Server is transferred to the contents of the Data Validation Certificate (just as trust in a CA is transferred to the public key certificates that it issues). 4. Functional Requirements for DVCS The DVCS MUST 1. provide a signed receipt in the form of a data validation certificate to the requester, as defined by policy. The DVCS service definition and the policy defines how much information that has been used by the DVCS service to determine the response status will be included in a data validation certificate, e.g., public key certificates, CRLs, OCSP, TSA and DVCS responses. 2. indicate in the data validation certificate whether or not the signed document, the public key certificate(s), or the data were validated, and, if not, the reason why the verification failed. 3. include a strictly monotonously increasing serial number in each of its certificates. 4. include a monotonically increasing time of day value or a time stamp token into each data validation certificate. 5. include within each signed data validation certificate a policy identifier to determine the trust and validation policy used for this signature. 6. sign each data certification token using a key generated exclusively for this purpose, have this property of the key indicated in the corresponding public key certificate, and include a reference to this certificate as a signed attributes in the signature. The [TSA] defines additional requirements: The DVCS protocols can be used as a replacement for the services defined in [TSA], in this case Adams, Sylvester, Zolotarev, Zuccherato [Page 5] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 the requirements of [TSA] apply to that service. A DVCS service may be combined with or use archiving and logging systems, in order to serve as a strong building block in non- repudiation services. 5. Data Certification Server Transactions A DVCS client prepares a Data Certification Request. The request always contains data for which validity, correctness or possession is to be certified. It may be required that a requestor signs a request, to prove that it came from a valid DVCS service's subscriber. The DVCS client chooses an appropriate transport mechanism to convey the requests to a DVCS. It may be necessary to choose a transport mechanism providing confidentiality and, in particular, allowing authentication of the DVCS by the requestor, e.g. TLS or encryption. The DVCS authenticates the request if necessary. If the request is valid, the DVCS performs all necessary verifications steps, and generates a Data Validation Certificate (DVC), and sends a response message containing the DVC back to the requestor. The Data Validation Certificate is a signed document (CMS SignedData). If the request was invalid, a response message will contain an appropriate error notification. Upon receiving the token, the requesting entity SHOULD verify its validity, i.e. it contains the correct time, the correct name for the DVCS, the correct request information and message imprint, a valid signature, and satisfactory status, service and policy fields. When verifying validity of a DVC, it is up to the requestor's application to check whether a DVCS's signing certificate DVCS was valid. Depending on the usage environment, different methods (online or out of band, CRLs, DVCS, OCSP...) may have to be used. After all checks passed, the data validation certificate can be used to authenticate the correctness or possession of the corresponding data. 6. Identification of the DVCS The DVCS MUST sign all data certification messages with a key reserved explicitly for that purpose. The corresponding certificate MUST contain the extended key usage field extension as defined in Adams, Sylvester, Zolotarev, Zuccherato [Page 6] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 [RFC2459] Section 4.2.1.14 with KeyPurposeID having value id-kp-DVCS. This extension MUST be marked as critical. The Data Validation Certificate MUST contain an ESSCertID authenticated attribute for the certificate used by the DVCS for signing. id-kp-DVCS OBJECT IDENTIFIER ::= { tbd } Consistent key usage bits: digitalSignature, nonRepudiation A DVCS's certificate MAY contain an Authority Information Access extension [RFC2459] in order to convey the method of contacting the DVCS. The accessMethod field in this extension MUST contain the OID id-ad-DVCS: id-ad-DVCS OBJECT IDENTIFIER ::= { tbd } The value of the field 'accessLocation' field defines the transport (e.g. an URL) used to access the DVCS. 7. Common Data Types There are several common data types that occur in the request and the response data structures. These data types are either defined by this document or imported from other sources. This chapter defines of these types and lists their usages. 7.1 DigestInfo: This element is defind in [RFC2315]. Since the status of that document the definition is repeated here: DigestInfo ::= SEQUENCE { digestAlgorithm DigestAlgorithmIdentifier, digest Digest } Digest ::= OCTET STRING The fields of type DigestInfo have the following meanings: - The field 'digestAlgorithm' identifies the message-digest algorithm (and any associated parameters) under which data are digested. - The field 'digest' is the result of the message-digesting process. A DigestInfo occurs in two places: - as a data portion for the ccpd service, and Adams, Sylvester, Zolotarev, Zuccherato [Page 7] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 - in all a data validation certificates to hold a digest of the data portion of the corresponding request or a copy of the data field for a ccpd service. 7.2. Nonce Requests and responses may include INTEGER values as nonce fields. A nonce field in the request is returned as is in the response, the DVCS may create an addition nonce in the response. 7.3. Time Values Indicators of time occur in requests and responses. In the most simple form, and genrated localloy either by a requester or a DVCS, they are represented as GeneralizedTime where fractions of seconds are allowed. An alternate form is a timeStampToken from a [TSA] or as a DVC, or as token from another third party service. When using third party tokens, it is a matter of policy whether a DVCS tries to interprete or validate a timeStampToken. DVCSTime ::= CHOICE { genTime GeneralizedTime, timeStampToken SignedData } Future versions of the protocol MAY include additional time formats. Time values generated by the DVCS are increasing but not necessarily unique using the order defined by serial numbers. 7.4. PKIStatusInfo This structure is defined in [RFC2510]. It is used as component of the 'chain' field of a TargetEtcChain structure, and as a global status indicator in the DVCSResponse structure. Every occurence of PKIStatusInfo is generated by the responding DVCS to reflect the result of some local verification. 7.5. TargetEtcChain A TargetEtcChain structure contains certificates and other indicators to describe either (in a request) information to be validated (in a cpkc service) or the result of the verifications. The structure may also contain information about policies and policy mappings. The details about how to fill in and to interpret the structure are Adams, Sylvester, Zolotarev, Zuccherato [Page 8] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 defined later for each service. the 'pathProcinput' field contains information about policies and policy mapping to be used or used a validation. If present, it contains the result of a local verification of the immediately preceeding element, or of the target value, if it is the first element in the 'chain' sequence. If no 'pkistatus' or 'certstatus' is present, the DVCS considers all elements in the 'chain' as trustworthy. Note, that there may be for example an OCSP response or DVC indicating an invalid certificate. TargetEtcChain ::= SEQUENCE { target CertEtcToken, chain [0] SEQUENCE SIZE (1..MAX) OF CertEtcToken OPTIONAL, pathProcInput [1] PathProcInput OPTIONAL } PathProcInput ::= SEQUENCE { acceptablePolicySet SEQUENCE SIZE (1..MAX) OF PolicyInformation, inhibitPolicyMapping BOOLEAN DEFAULT FALSE, explicitPolicyReqd BOOLEAN DEFAULT FALSE } CertEtcToken ::= CHOICE { certificate [0] Certificate , oscpcertid [1] CertId , esscertid [2] ESSCertId , datacert [3] SignedData , oscpresponse [4] OCSPResponse, crl [5] CertificateList, certstatus [6] CertStatus, pkistatus [7] PKIStatusField , extension Extension } Certificate, PolicyInformation and CertificateListare are defined in [RFC2459]. ESSCertId is defined in [RFC2634]. CertiId, OCSPResponse and CertStatus are defined in [RFC2560]. PKIStatusField is defined in [RFC2510]. The choice 'datacert' can contain a data validation certificate, or a timeStamp, or other assertions. The choices 'datacert', 'ocspresponse' and 'crl' are provided by services external to the responding DVCS. The choices 'certStatus' Adams, Sylvester, Zolotarev, Zuccherato [Page 9] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 and 'pkistatus' reflect decisions made directly by the responding DVCS. As a replacement for certificates, certification identifiers (ESSCertId, CertId) MAY be used in requests and responses, if this is sufficient to perform the service, e.g., when the corresponding certificates are provided elsewhere in a request or response (as part of the SignedData type). 7.6. DVCSReqInfo A DVCSReqInfo data structure contains general information about the data validation and certification request. This structure occurs in a request, and included in a corresponding data validation certificate. DVCSReqInfo ::= SEQUENCE { service ServiceType, requester [0] GeneralNames OPTIONAL, reqPolicy [1] PolicyInformation OPTIONAL, DVCS [2] GeneralNames OPTIONAL, dataLocator [3] GeneralName OPTIONAL, nonce Integer, reqTime DVCSTime OPTIONAL, extensions Extensions OPTIONAL } The ServiceType type indicates the DVCS service type of a request. See chapter 2 for a description of the services. ServiceType ::= INTEGER { cpd(1), vsd(2), cpkc(3), ccpd(4) } 7.7. GeneralNames There are several occurences of sequences of GeneralName. For syntactical conveniance the following type is defined here: GeneralNames ::= SEQUENCE OF GeneralName GeneralName is imported from [RFC2459]. 8. Data Validation and Certification Requests A data certification request is a SignedData construct of [RFC2630]. The contenttype indicated in the eContentType of the encapContentInfo is of type id-ct-DVCSReqData signalling a DVCSReqData as eContent of the encapContentInfo (carried as an octet string). id-ct-DVCSReqData OBJECT IDENTIFIER ::= { tbd } Adams, Sylvester, Zolotarev, Zuccherato [Page 10] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 A data certification request MAY contain several SignerInfo structures, and countersignature attributes depending on operational environments. When an end user client creates the request, there is one or zero SignerInfo. A relaying DVCS MAY add an additional signature or a countersignature attribute. The content of a request consists of a description of the desired service and additional parameters, the data to be validated, and an optional identifier of the request. DVCSRequest ::= SEQUENCE { reqInfo DVCSReqInfo, data Data, transactionIdentifier GeneralName OPTIONAL } The 'reqInfo' element contains general information about the request. It is filled in by the requester as follows: - The field 'service' contains the requested service. - The value of the 'requester' field indicates the requesting entity. If the field is present, and the request is signed, it MUST match the identity (subjectName or subjectAltName extension) of the corresponding signature certificate, unless the request is signed by a DVCS (relaying a request to another server). When acting as a relay to DVCS MAY its own identity in the request relayed to another service provider, and it MAY remove the initial value. - The 'reqPolicy' field SHOULD indicate the policy under which the certification is requested. This field MUST be checked by the DVCS to verify agreement with its own policy. The absence of this field indicates that any policy is acceptable. - The 'dvcs' field MAY indicate a list a DVCS which are to be contacted to provide (additional) information or to perform additional operations necessary to produce the response. It is up to the DVCS policy whether to honor this field or not, and to define which choice of a general name is acceptable (e.g. an URL or a DN). The DVCS MAY use local information to use additional external services. - The 'dataLocator' field MAY indicate where a copy of the 'data' field of the request or supplementary information can be obtained. The DVCS does not use this field for its own operation, the exact interpretation of this field is defined by applications. Adams, Sylvester, Zolotarev, Zuccherato [Page 11] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 - The 'nonce' field MAY be used to provide additional protection against replay or content guessing attacks. - The 'reqTime' field MAY be used to indicate the time for which the requested service should be performed. For a vsd and cpkc service, it indicates to check whether the signed document or certicates where valid at the given time. For the other service, the field is ignored by the DVCS. If the field is absent, the current time of the DVCS is assumed. - The 'extensions' field MAY be used to include additional information. Extensions may be marked critical or not in order to indicate whether the DVCS is supposed to understand them. This document does not define extensions. The Data type is defined as a placeholder for service-specific content, defined by each particular service provided by the DVCS. Depending on the requested service type, the field may contain requester-specific data, a signed document, a list of certificates, a message digest or arbitrary data. Data ::= CHOICE { message [0] OCTET STRING , messageImprint [1] DigestInfo, certs [2] SEQUENCE SIZE (1..MAX) OF TargetEtcChain, } The requester fills the 'data' element as follows: - For a vsd service request, the requestor encapsulates a CMS SignedData object in the value octets of the 'message' choice. It is up to the requester to provide any certificate that may be needed to verify the signature(s) in the signedData object. The requester MAY choose to remove all certificates from the signedData (since they are not part of the signed part anyway, and transfer them in the certificate list of the signedData structure containing the DVCSRequest. - For a cpkc service request the certs choice is used. Each certificate to be verified MUST be included in a separate instance of TargetEtcChain. The target field SHALL contain the cert to be verified and the chain field, if present, MUST indicate the chain of trust to be used when certifying the certificate. The pathProcInput field, if present, SHOULD indicate the acceptable Adams, Sylvester, Zolotarev, Zuccherato [Page 12] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 policy set and initial settings for explicit-policy-indicator and inhibit-policy-mapping indicators to be used in X.509 public key certificate path validation (see [RFC2459]). Only the Certificate, ESSCertId, CertId or Extension fields of the TargetEtcChain can be used in the request. The requester is responsible to provide sufficient information to the DVCS to identify the corresponding certificates. - For a ccpd service the messageImprint choice is used. The hash algorithm indicated in the hashAlgorithm field SHOULD be a "strong" hash algorithm (that is, it SHOULD be one-way and collision resistant). It is up to the Data Certification Server to decide whether or not the given hash algorithm is sufficiently "strong" (based on the current state of knowledge in cryptanalysis and the current state of the art in computational resources, for example). - For a cpd service the message choice is used. The field 'message' contain requester-specific data with any type of content. The DVCS does not inspect, modify, or take any particular action based on the particular content of the 'message' field. The element 'transactionIdentifier' MAY be used in order to permit to associate DVCS responses containg error messages, to requests. For example, in a mail based environment, the parameter could be a copy of a messageid. Note, that the transactionIdentifier is not necessary for associating a request with a data validation certificate. 9. DVCS Responses This chapters describes the data structures that are created by a DVCS to indicate the results of validation and certification requests. A DVCS Response structure is generated by the DVCS as a result of processing of the data certification validation request. A Data Validation response is a SignedData construct of [RFC2630]. The contenttype indicated in the eContentType of the encapContentInfo is of type id-ct-DVCSResponseData, signalling a DVCSResponse as eContent of the encapContentInfo (carried as an octet string). Adams, Sylvester, Zolotarev, Zuccherato [Page 13] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 id-ct-DVCSResponseData OBJECT IDENTIFIER ::= { tbd } The DVCS MUST use a key, specifically allocated for the purpose of DVCS signing, with a proper extendedKeyUsage set in a corresponding certificate. In a critical situation when a DVCS can not produce a valid signature (if the DVCS's signing key is known to be compromised, for example), the DVCSResponse must be generated as a signedData with no signerInfo attached. In this case, the response MUST only contain the error notification. Receiving unsigned DVCSResponse MUST be treated by the clients as critical and fatal error, and the content of the message should not be implicitly trusted. A valid response can contain one of the following: 1. A Data Validation Certificate (DVC), containing the results of data validation operations, performed by the DVCS. 2. An error notification. This may happen when a request fails due to a parsing error, requester authentication failure, or anything else that prevented the server from executing the request. The following type is used: DVCSResponse ::= CHOICE { dvcErrorNote [0] DVErrorNote, dvCertInfo [1] DVCertInfo } 9.1. DVCS Error Notification A DVCS Error Notification is a CMS signedData object (maybe with signature) containing a DVCSResponse with a dvErrorNote choice. DVErrorNote ::= SEQUENCE { DVTransStatus PKIStatusInfo , transactionIdentifier GeneralName OPTIONAL } The PKIStatusInfo is defined in the [RFC2511]. For the purposes of communicating the DVErrorNote, the following subset PKIFailureInfo for use in PKIStatusInfo is used: PKIFailureInfo ::= BITSTRING { badRequest (2), -- transaction not permitted or supported Adams, Sylvester, Zolotarev, Zuccherato [Page 14] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 badTime (3), -- messageTime was not sufficiently close to the system time, -- as defined by local policy badDataFormat (5), -- the data submitted has the wrong format wrongAuthority (6), -- the DVCS indicated in the request is different from the -- one creating the response token incorrectData (7), --the requester's data (i.e. signature) is incorrect ) In the DVError, the PKIStatus field of the PKIStatusInfo must be set to REJECTED. The 'statusString' field of PKIStatusInfo can be used to include reason text such as for example "Invalid request format". The DVCS fills the 'transactionIdentifier' with a copy of the 'transactionIdentifier' field of the corresponding DVCSRequest. 9.2. Data Validation Certificate A Data Validation Certificate is a signedData object containing a DVCSResponse with a dvCertInfo choice. DVCertInfo::= SEQUENCE { nonce INTEGER OPTIONAL, dvReqInfo DVCSReqInfo, messageImprint DigestInfo, serialNumber Integer, respTime DVCSTime, dvStatus [0] PKIStatusInfo OPTIONAL, policy [1] PolicyInformation OPTIONAL, reqSignature [2] SignerInfos OPTIONAL, certs [3] SEQUENCE OF TargetEtcChain OPTIONAL, extensions [4] Extensions OPTIONAL } The DVCertInfo structure is returned as a result of successful execution of data validation service. It contains the results of the data validation, a reference to the original request, and other parameters. Please note that 'successful execution' does not necessarily mean that the validation itself was successful, a DVCertInfo may contain both the 'valid' and 'invalid' results. The DVCS fille a DVCertInfo as follows: Adams, Sylvester, Zolotarev, Zuccherato [Page 15] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 - The field 'nonce' MAY be used to protect against replay attacks. - The dvReqInfo is essentially a copy of the 'reqInfo' field of the corresponding request. The DVCS MAY modify the fields 'dvcs' and 'requester' of the ReqInfo structure, to indicate DVCS that participated in the verification and certification. - The field 'messageImprint' is a computed from the 'data' field of the corresponding request as follows: For the 'certs' choice, the digest is computed over the DER encoded data value. For a 'message' choice the digest is computed over the value octets (not including tag and length octets) of the OCTET STRING. It is up to the DVCS to choose an appropriate digest algorithm. For a 'messageImprint' choice, the 'messageImprint' of the DVCSRequest is copied as is. - The field 'serialNumber' contains a unique identifier of the request. - The field 'respTime' indicates a time value associated to the response. The value MAY be a locally generated one, or a signed TimeStampToken (TST) or DVC obtained from an external service. - The field 'dvStatus' reflects a collective status of the validation. An omitted 'dvStatus' field implies SUCCESS, except in case of a cpkc service, where each element of the 'certs' field have their own independant status. If the 'dvStatus' is set for a cpkc service response, this is equivalent to putting an identical one into each element of 'certs' field as a last element in the 'chain' field. If the field 'dvStatus' does not indicate success ('granted' or 'granted with mods') the element 'failInfo' MAY indicate the reason for the failure. Note that the field 'certs' MAY contain additional information about verification failures. A failure of the verification of one of the signatures does not necessarily result in the production of an error message. For example, as long as a sufficient number of signature verifications was successful, a DVC with status `grantedWithMods` is be produced. A DVC with status `granted` MUST only be produced if all signatures verified successfully. The field MUST be present, and the status MUST be set to FAILED, if Adams, Sylvester, Zolotarev, Zuccherato [Page 16] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 the data validation has failed to successfully verify all or some of the data. The field MUST be present, and the status must be set to WAITING, if there is no or only an incomplete response immediately available. In the situation when the data validation fails, the requestor can further investigate the cause of the failure, by looking into the TargetEtcChain fields. 'pkistatus' fields in the TargetEtcChain will indicate which item(s) has failed the validation and for what reason. - The 'policy' field indicates the policy under which the DVCS operates. - If present, 'reqSignature' MUST be the same value as the signerInfos field of the corresponding request. It is a policy decision whether to include this field. - The 'certs' field contains the results is the verifications made by the DVCS. For the cpkc service each element contains a copy of a corresponding field of the request plus the result of the verfications or external certification. For a vsd service each element contains the result of the validation of one signature of the signed document to be validated. The 'policyReturnInfo' fields indicate the policies and mappings that were processed during X.509 public key certificate path validation. PolicyMappingsSyntax is defined in [RFC2459]. - The 'extensions' field MAY be used to return additional information to the client. Extensions MAY be marked critical or not in order to indicate whether the client is supposed to understand them. This document does not define extensions. 10. Transports There is no mandatory transport mechanism in this document. All mechanisms are optional. 10.1 DVCS Protocol via HTTP or HTTPS This subsection specifies a means for conveying ASN.1-encoded messages for the DVCS protocol exchanges via the HyperText Transfer Protocol. The DER encoded DVCS requests and responses are encapsulated using a Adams, Sylvester, Zolotarev, Zuccherato [Page 17] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 simple MIME object with Content-Type application/dvcs and an appropriate Content-Transfer-Encoding. This MIME object can be sent and received using common HTTP processing engines over WWW links and provides a simple browser- server transport for DVCS messages. 10.2 File Based Data Protocol A file containing a data validation and certification message MUST contain only the DER encoding of one PKI message, i.e. there MUST be no extraneous header or trailer information in the file. Such files can be used to transport data certification messages using for example, FTP. 10.3 Data Certification Server Protocol Using Email This section specifies a means for conveying ASN.1-encoded messages for the protocol exchanges described in Section 4 via Internet mail. The DER encoded DVCS requests and responses are encapsulated using a simple MIME object with Content-Type application/dvcs with an appropriate Content-Transfer-Encoding. This MIME object can be sent and received using MIME processing engines and provides a simple Internet mail transport for Data Validation and Certification Server messages. 11. Security Considerations This entire chapter discusses security considerations. When designing a data validation and certification service, the following considerations have been identified that have an impact upon the validity or "trust" in the data validation certificate. 1. The enclosed public key certificate is revoked or the signer's key is compromised and the corresponding public key certificate is revoked before the DVCS acts upon the request. The DVCS is REQUIRED to validate appropriate information within the request before it constructs the data certification token. It is therefore mandated that the DVCS have access to current information regarding public key certificate status before it creates the token. In this situation, the certification process would produce an error. 2. The enclosed public key certificate is revoked or the signer's key Adams, Sylvester, Zolotarev, Zuccherato [Page 18] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 is compromised and the corresponding certificate is revoked after the DVCS acts upon the request. This is not a concern to the DVCS, once the DVCS has constructed the DVC, as long as the compromise date in the CRL is not before the time of certification. If it is, this situation would have to be handled by off-line, possibly human-aided, means specific to the situation at hand. 3. The DVCS's private key is compromised and the corresponding certificate is revoked. In this case, any DVC signed by the DVCS cannot be trusted. For this reason, it is imperative that the Data Certification Server's key be guarded with proper security and controls in order to minimize the possibility of compromise. Nevertheless, in case the private key does become compromised, an audit trail of all the DVC generated by the DVCS SHOULD be kept as a means to help discriminate between genuine and false DVCs. 4. The DVCS signing key MUST be of a sufficient length to allow for a sufficiently long lifetime. Even if this is done, the key will have a finite lifetime. Thus, any DVCs signed by the DVCS SHOULD be time stamped (if authentic copies of old CRLs are available) or certified again (if they aren't) at a later date to renew the trust that exists in the DVC's signature. Data validation certificates could also be kept with an Evidence Recording Authority [ISONR] to maintain this trust. 5. When there is a reason to believe that the DVCS can no longer be trusted, its certificate MUST be revoked. Thus, at any future time the DVCs signed with the corresponding key will not be trusted. 6. In certain circumstances, a DVCS may not be able to produce a valid response to a request (for example, if it is unable to compute signatures for a period of time). In these situations the DVCS MAY create a response that only contain a PKIStatusInfo. 7. DVCS clients SHOULD NOT trust unsigned responses. A DVCS client may trust unsigned responses, if the communication channel provides for server authentication (e.g. by services defined by TLS [RFC2246]). 8. Client identification and authentication MAY use services defined by TLS [RFC2246]) instead of using a signed request. 9. When confidentiality and server authentication is required, requests and responses MAY be protected using appropriate mechanisms (e.g. CMS encapsulation [RFC 2630] or TLS [RFC2246]). 12. Patent Information Adams, Sylvester, Zolotarev, Zuccherato [Page 19] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 The following United States Patents related to data validation and certification services, listed in chronological order, are known by the authors to exist at this time. This may not be an exhaustive list. Other patents may exist or be issued at any time. Implementers of the DVCS protocol and applications using the protocol SHOULD perform their own patent search and determine whether or not any encumberences exist on their implementation. # 4,309,569 Method of Providing Digital Signatures (issued) January 5, 1982 (inventor) Ralph C. Merkle (assignee) The Board of Trustees of the Leland Stanford Junior University # 5,001,752 Public/Key Date-Time Notary Facility (issued) March 19, 1991 (inventor) Addison M. Fischer # 5,022,080 Electronic Notary (issued) June 4, 1991 (inventors) Robert T. Durst, Kevin D. Hunter # 5,136,643 Public/Key Date-Time Notary Facility (issued) August 4, 1992 (inventor) Addison M. Fischer (Note: This is a continuation of patent # 5,001,752.) # 5,136,646 Digital Document Time-Stamping with Catenate Certificate (issued) August 4, 1992 (inventors) Stuart A. Haber, Wakefield S. Stornetta Jr. (assignee) Bell Communications Research, Inc., # 5,136,647 Method for Secure Time-Stamping of Digital Documents (issued) August 4, 1992 (inventors) Stuart A. Haber, Wakefield S. Stornetta Jr. (assignee) Bell Communications Research, Inc., # 5,373,561 Method of Extending the Validity of a Cryptographic Certificate (issued) December 13, 1994 (inventors) Stuart A. Haber, Wakefield S. Stornetta Jr. (assignee) Bell Communications Research, Inc., # 5,422,95 Personal Date/Time Notary Device (issued) June 6, 1995 (inventor) Addison M. Fischer # 5,781,629 Digital Document Authentication System Adams, Sylvester, Zolotarev, Zuccherato [Page 20] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 (issued) July 14, 1998 (inventor) Stuart A. Haber, Wakefield S. Stornetta Jr. (assignee) Surety Technologies, Inc., 10. References [RFC2119] "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119. [TSA] C. Adams, P. Cain, D. Pinkas, R. Zuccherato, "Internet X.509 Public Key Infrastructure, Time Stamp Protocols," draft-ietf-pkix- time-stamp-02.txt, 1999 (work in progress). [RFC2510] C. Adams, S. Farrell, "Internet X.509 Public Key Infrastructure, Certificate Management Protocols," RFC-2510, 1999. [RFC2459] R. Housley, W. Ford, W. Polk, D. Solo, "Internet X.509 Public Key Infrastructure, Certificate and CRL Profile", RFC-2459. January 1999. [RFC2630] R. Housley, "Cryptographic Message Syntax", RFC-2630, June 1999. [ISONR] ISO/IEC 10181-5: Security Frameworks in Open Systems. Non- Repudiation Framework. [RFC2119] Key works for use in RFCs to Indicate Requirement Levels, S. Bradner, RFC 2119, March 1997. [RFC2511] M. Myers, C. Adams, D. Solo, D. Kemp "Internet X.509 Certificate Request Message Format," RFC-2511, March 1999. [RFC2246] T. Dierks, C. Allen, "The TLS Protocol, Version 1.0," RFC 2246, January 1999. [RFC2634] P. Hoffman, "Enhanced Security Services for S/MIME", RFC 2634, June 1999 [RFC2560] M. Myers, R. Ankney, A. Malpani, S. Galperin, C. Adams, "X.509 Internet Public Key Infrastructure Online Certificate Status Protocol", RFC 2560, June 1999. 11. Authors' Addresses Carlisle Adams Entrust Technologies 750 Heron Road Adams, Sylvester, Zolotarev, Zuccherato [Page 21] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 Ottawa, Ontario K1V 1A7 CANADA cadams@entrust.com Peter Sylvester EdelWeb SA 33 avenue du Maine F-75755 Paris Cedex 15 FRANCE peter.sylvester@edelweb.fr Michael Zolotarev Baltimore Technologies Pty Limited, 5th Floor, 1 James Place, North Sydney, NSW 2060. AUSTRALIA mzolotarev@baltimore.com Robert Zuccherato Entrust Technologies 750 Heron Road Ottawa, Ontario K1V 1A7 CANADA robert.zuccherato@entrust.com APPENDIX A - PKCS #9 Attrubute We define a PKCS #9 [PKCS9] attribute type. This attribute type MAY be included as a signed attribute of the SignedData object. The attribute type has ASN.1 type SignedData and contains a dvc (as defined in this document). The object identifier id-DVCS-dvc identifies the dcs token attribute type. id-DVCS-dvc OBJECT IDENTIFIER ::= { tbd } The attribute may be used as a authenticated or unauthenticated attribute in CMS SignedData documents. APPENDIX B - Signed document validation. We present some examples of a possible use of DVCS in the context of validation signed documents. Adams, Sylvester, Zolotarev, Zuccherato [Page 22] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 B.1 Signed document validation The example covers the case where a DVCS is used by a signer to obtain a proof that a document's structure, including one or more attached signatures, is/was correct, after the document was signed. The certificate can be provided either by a DVCS that is trusted by the signer, or by a DVCS that is trusted by an intened verifier of the document. The signer get's an evidence that its intentions were good and it produced a signed document using the environment(keys, algorithms, etc) that was known to be OK. It produces a stand-alone document that can be used to extend the life of a signature. This example assumes that we have total trust in the Data Validation and Certification Server. Signature algorithms and keys have a definite lifetime. Therefore, signatures have a definite lifetime. The Data Certification Server can be used to extend the lifetime of a signature. In order to extend the lifetime of a signature in this way, the following technique MAY be used. A) The signature needs to be certified. 1) The signed message is presented to the Data Validation and Certification Server in the data field of DVCSReqInfo under service type cs and an appropriate policy. 2) The Data Validation and Certification Server verifies that the signature and verification key are valid at that time by checking expiry dates and status information, and returns a data certification token. B) The certified signature MUST be verified. 1) The signature of the Data Validation and Certification Server in data certification token SHALL be verified using the Data Certification Server's valid verification key. In this situation the signer's signing key (and therefore, its signature) is only valid until some specified time T1. The DVCS's signing key (and therefore, its signature) is valid until some specified time T2 that is (usually) after time T1. Without certification, the signer's signature would only be valid until time T1. With certification, the signer's signature remains valid until Adams, Sylvester, Zolotarev, Zuccherato [Page 23] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 time T2, regardless of subsequent revocation or expiry at time T1. If the signature of the DVCS is valid, the trust we have in the DVCS allows us to conclude that the original signature on the data was valid at the time included in the dcsInfo field of the data certification token. APPENDIX C - Verifying the Status of a Public Key Certificate We now present two examples of how to produce a data validation certificate that can be used to assert that a public key certificate is valid, trusted, and can be used for a particular purpose. A client wants to use a given public key certificate either to use it in a signature or to use it it for document encryption. A DVCS MUST have access to current information regarding public certificate status, it can therefore be used to verify the revocation status of a certificate in at the current time. The following technique is used: A) The public key certificate needs to be validated and certified. 1) The certificate is presented to the Data Certification Server in the data field of DVCSReqInfo under service type cpkc and an appropriate policy. 2) The Data Validation and Certification Server verifies that the public key certificate is valid and that it hasn't been revoked and then returns a data validation certificate. B) The data validation certificate MUST be verified. 1) The signature of the Data Certification Server in the data certification token SHALL be verified using the Data Validation and Certification Server's valid verification key. C) The public key certificate is used. 1) A clients's own public key certificate (i.e., the corresponding private key) can be used to add a signature to a document. The signing certificate and the data validation certificate are added as signed attributes to the signature. A data validation certificate can now be used when verifying signatures using the key contained in the public key certificate. This service provided by the DVCS can be thought of Adams, Sylvester, Zolotarev, Zuccherato [Page 24] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 as a supplement to the usual method of checking revocation status. In other words, signature validation at a later time does not necessarily require access to the revocaton status of the user's signing certificate, access to a DVCS service and validation of the DVC is sufficient to validate the signed document. 2) A public key certificate for for key exchange can be used after having obtained a data validation certification certificate to encrypt data. The DVC can be stored with the data and/or stored by the creator of the encrypted document. If an intended recipient of the document claims that the creator did not use an appropriate encryption key, the DVC (obtained by a recipient's DVCS) can be used as evidence that the recipient's DVCS has authorized the usage of the public key. Appendix D - MIME Registration To: ietf-types@iana.org Subject: Registration of MIME media type application/timestamp MIME media type name: application MIME subtype name: dvcs Required parameters: None Optional parameters: None Encoding considerations: binary or Base64 Security considerations: Carries a request for a data validation and certification service and the response. A request may be cryptographically signed. The response will be cryptographically signed. Interoperability considerations: None Published specification: IETF PKIX Working Group Draft on Data Validation and Certification Server Protocols Applications which use this media type: Data Validation and Certification Server clients Additional information: Adams, Sylvester, Zolotarev, Zuccherato [Page 25] draft-ietf-pkix-dcs-02.txt DVCS Protocols October 12, 1999 Magic number(s): None File extension(s): .dvc Macintosh File Type Code(s): none Person & email address to contact for further information: Peter Sylvester Intended usage: COMMON Author/Change controller: Peter Sylvester Appendix E - Acknowledgements This text is based on initial work from Robert Zuccerato and Carlisle Adams, both at Entrust Technologies, and from Denis Pinkas at Bull, for time stamping, notary and data certification services. Appendix F - Full Copyright Statement Copyright (C) The Internet Society 1999. 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 shall 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. Adams, Sylvester, Zolotarev, Zuccherato [Page 26]