INTERNET DRAFT Mats Jansson, LiNK draft-ietf-ediint-as1-02.txt Chuck Shih, Actra Nancy Turaj, Mitre Corp. Rik Drummond, Drummond Group 19 November, 1996 MIME-based Secure EDI Status of this Memo This document is 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.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract This document describes how to securely exchange EDI documents using MIME and public key cryptography. Feedback Instructions: If you want to provide feedback on this draft, follow these guidelines: -Send feedback via e-mail to mjansson@agathon.com, with "AS#1" in the Subject field. -Be specific as to what section you are referring to, preferably quoting the portion that needs modification, after which you state your comments. -If you are recommending some text to be replaced with your suggested text, again, quote the section to be replaced, and be clear on the section in question. -If you are questioning fundamental methods, make it clear to us and we will bring the issue to the ediint list for discussion. To follow the discussion, you need to subscribe at ietf-ediint@imc.org. Table of Contents 1. Introduction 2. Overview 2.1 Purpose of a security guideline for MIME EDI 2.2 Definitions 2.2.1 Terms 2.2.2 The secure transmission loop 2.2.3 Definition of receipts 2.3 Assumptions 2.3.1 EDI process assumptions 2.3.2 Flexibility assumptions 3. Structure of an EDI MIME message 3.1 Referenced RFCs and their contribution 3.1.1 RFC 821 SMTP [7] 3.1.2 RFC 822 Text Message Format [3] 3.1.3 RFC 1521 MIME [1] 3.1.4 RFC 1847 MIME Security Multiparts [6] 3.1.5 RFC 1892 Multipart/report [9] 3.1.6 RFC 1767 EDI Content [2] 3.1.7 RFC 2015 PGP/MIME [4] 3.1.8 Internet draft (fajman): Message Disposition Notification [5] 3.1.9 RSA Specifications - S/MIME (RSA Security, Inc.) [8] 3.2 Vocabulary 3.3 Structure of an EDI MIME message - No encryption/No signature 3.4 Structure of an EDI MIME message - S/MIME 3.4.1 S/MIME Overview 3.4.2 Example: S/MIME - Signature Only 3.4.3 Example: S/MIME - Encryption Only 3.4.4 Example: S/MIME - Signature and Encryption 3.5 Structure of an EDI MIME message - PGP/MIME 3.5.1.PGP/MIME Overview 3.5.2 Example: PGP/MIME - Signature Only 3.5.3 Example: PGP/MIME - Encryption Only 3.5.4 Example: PGP/MIME - Signature and Encryption 4. Receipts 4.1 Introduction 4.2 Requesting a signed receipt 4.3 Message Disposition Notification Format 4.4 Message Disposition Notification Processing 4.4.1 Large File Processing 4.4.2 Example 5. Public key certificate handling 5.1 Near term approach 5.2 Long term approach 6. Authors' Addresses 7. References 1. Introduction The authors would like to extend special thanks to Carl Hage for providing the team with valuable, and very thorough feedback. Without participants like Carl, these efforts become hard to complete in a way useful to the users of the technology. Previous work on Internet EDI focused on specifying MIME content types for EDI data ([2] RFC 1767). This Applicability Statement expands on RFC 1767 to specify use of a comprehensive set of data security features, specifically data privacy, data integrity/authenticity, non-repudiation of origin and non- repudiation of receipt. This draft recognizes contemporary RFCs and Internet drafts and is attempting to "re-invent" as little as possible. With an enhancements in the area of "receipts", as described below (3.1.8), secure Internet MIME based EDI can be accomplished by using and complying with the following RFCs and drafts: -RFC 821 SMTP -RFC 822 Text Message Formats -RFC 1521 MIME -RFC 1767 EDI Content Type -RFC 1847 Security Multiparts for MIME -RFC 1892 Multipart/Report -Internet draft: Message Disposition Notification (fajman) -RFC 2015 MIME/PGP (elkins) -Internet draft: S/MIME Specification (dusse) Our intent here is to define clearly and precisely how these are pieced together and what is required by user agents to be compliant with this Applicability Statement. 2. Overview 2.1 Purpose of a security guideline for MIME EDI The purpose of these specifications is to ensure interoperability between EDI user agents, invoking some or all of the commonly expected security features. This standard is also NOT limited to strict EDI use, but applies to any electronic commerce application where business data needs to be exchanged over the Internet in a secure manner. 2.2 Definitions 2.2.1. Terms EDI Electronic Data Interchange EC Electronic Commerce Receipt The functional message that is sent from a receiver to a sender to acknowledge receipt of an EDI/EC interchange Signed Receipt Same as above, but with a digital signature Message Disposition The way by which a receipt or a signed Notification (MDN) receipt is accomplished within Internet Messaging. Non-repudiation of NRR is a "legal event" that occurs when the Receipt (NRR) original sender of an EDI/EC interchange has verified the signed receipt coming back from the receiver. NRR IS NOT a functional or a technical message. PGP/MIME Digital envelope security based on the Pretty Good Privacy (PGP) standard (Zimmerman), integrated with MIME Security Multiparts [6]. S/MIME A protocol for adding cryptographic signature and/or encryption services to Internet MIME messages. 2.2.2 The secure transmission loop The functional requirements document, [9] "Requirements for Inter- operable Internet EDI" (can be found at www.ietf.org),provides extensive information on EDI security and the user/business related processes surrounding the need for and use of EDI security. In this document, it is assumed that the reader is familiar with the requirements document. This document's focus is on the formats and protocols for exchanging EDI content that has had security applied to it using the Internet's messaging transport. The "secure transmission loop" for EDI involves one organization sending a signed and encrypted EDI interchange to another organization, requesting a "signed receipt", followed later by the receiving organization sending this "signed receipt" back to the sending organization. In other words, the following transpires: -The organization sending EDI/EC data encrypts the data and provides a digital signature, using either PGP/MIME or S/MIME. In addition, they request a "signed receipt". -The receiving organization decrypts the message and verifies the signature, resulting in verified integrity of the data and authenticity of the sender. -The receiving organization then sends a "signed receipt" in the form of a signature over the hash from the previous step. The above describes functionality which if implemented, would satisfy all security requirements. This specification, however, leaves full flexibility for users to decide the degree to which they want to deploy those features with their EDI trading partners. 2.2.3 Definition of receipts The term used for both the functional activity and message for acknowledging receipt of an EDI/EC interchange is "receipt", or "signed receipt". The first term is used if the acknowledgment is for an interchange that was not signed, thereby resulting in a receipt which is also not signed. The second term is used if the acknowledgment is for an interchange which was signed, resulting in a receipt which is also signed. The rule is: If a receipt is requested, it will be signed only if the original interchange was signed. A term often used in combination with receipts is "Non- repudiation of Receipt (NRR). NRR refers to a legal event which occurs only when the original sender of an interchange has verified the sender and content of a "signed receipt". Note that NRR is not possible without signatures. 2.3 Assumptions 2.3.1 EDI process assumptions -Encrypted object is an EDI Interchange This specification assumes that a typical EDI interchange is the lowest level object that will be subject to security features. In ANSI X12, this means anything between, and including segments ISA and IEA. In EDIFACT, this means anything between, and including, segments UNA/UNB and UNZ. In other words, the EDI interchanges including envelope segments remain intact and unreadable during secure transport. -EDI envelope headers are encrypted Congruent with the above statement, EDI envelope headers are NOT visible in the MIME package. In order to optimize VAN-to- Internet routing, work may need to be done in the future to define ways to pull out some of the envelope information to make them visible, however, this specification does not go into any detail on that. -X12.58 and UN/EDIFACT security considerations The most common EDI standards, ANSI X12 and EDIFACT, have defined internal provisions for security. X12.58 is the security mechanism for ANSI X12 and AUTACK provides security for EDIFACT. This specification DOES NOT dictate use or non-use of these security standards. They are both fully compatible, though possibly redundant, with this specification. 2.3.2 Flexibility assumptions -Encrypted or un-encrypted data This specification allows for EDI message exchange where the EDI data is either un-protected or protected by means of encryption. -Signed or un-signed data This specification allows for EDI message exchange with or without digital signature of the original EDI transmission. -Use of receipt or not (signature required for "Signed Receipt") This specification allows for EDI message transmission with or without a request for receipt notification. If receipt notification is requested, however, a signature is required as part of both the original EDI transmission and the returned receipt. -Formatting choices This specification defines use of two methods for formatting EDI contents that have security applied to it: -PGP/MIME -S/MIME This specification relies on the guidelines set forth in the Internet draft on PGP/MIME, as reflected in [4] MIME Security with Pretty Good Privacy (PGP), and [8] S/MIME Specification from RSA Security, Inc. Compliance with this specification dictates that AT LEAST one of these methods is supported. -Hash function, message digest choices When signature is used, unless specified otherwise by the chosen method (PGP/MIME or S/MIME), the MD5 checksum hash function is recommended. In summary, the following eight permutations are possible, in any given trading relationship: (1) Sender sends un-encrypted data, does NOT request a receipt. (2) Sender sends unencrypted data, requests a receipt. Receiver sends back a receipt. (3) Sender sends encrypted data, does NOT request a receipt. (4) Sender sends encrypted data, requests a receipt. Receiver sends back a receipt. (5) Sender sends signed data, does NOT request a signed receipt. (6) Sender sends signed data, requests a signed receipt. Receiver sends back a signed receipt. (7) Sender sends encrypted and signed data, does NOT request a signed receipt. (8) Sender sends encrypted and signed data, requests a signed receipt. Receiver sends back a signed receipt. NOTE: Users can choose any of the eight possibilities, but only example (8) offers the whole suite of security features described in the "Secure transmission loop" above. NOTE: A request for receipt that is signed, MUST result in a signed receipt. A request for receipt without signature MUST result in an un-signed receipt. 3. Structure of an EDI MIME message The following sub chapters describe the structure of EDI MIME messages, making use of security features in different ways. Please note that if a signed receipt is to be returned, the original EDI transmission also had to have been signed. The structures shown below represent the use of specifications outlined in the following RFCs and Internet-drafts, and before moving into the structures themselves, there is a brief review of what each document contributes. NOTE: The examples below are just that - examples. Do not code according to them. Refer to the RFCs that specify the correct grammar in each case. 3.1 Referenced RFCs and their contribution 3.1.1 RFC 821 SMTP [7] This is the core mail transfer standard that all MTAs need to adhere to. 3.1.2 RFC 822 Text Message Format [3] Defines message header fields and the parts making up a message. 3.1.3 RFC 1521 MIME [1] This is the basic MIME standard, upon which all MIME related RFCs build, including this one. Key contributions include definition of "content type" and sub-type "multipart", in addition to encoding guidelines, which establish 7-bit US-ASCII as the lowest common denominator used. 3.1.4 RFC 1847 MIME Security Multiparts [6] This document defines security multiparts for MIME: multipart/encrypted and multipart/signed. \ 3.1.5 RFC 1892 Multipart/report [10] This RFC defines the use of Multipart/report content type, something that the MDN draft (fajman) relies on for the receipt functionality. 3.1.6 RFC 1767 EDI Content [2] This RFC defines the use of content type "application" for ANSI X12 (application/EDI-X12), EDIFACT (application/EDIFACT) and mutually defined EDI (application/EDI-Consent). 3.1.7 RFC 2015 PGP/MIME [4] This RFC defines the use of content types "multipart/encrypted", "multipart/signed", "application/pgp encrypted" and "application/pgp-signature" for defining MIME PGP content. 3.1.8 Internet draft (fajman): Message Disposition Notification [5] This Internet draft defines how a message disposition notification (MDN) is requested, and the structure of the MDN. NOTE: This is the only specification we were not able to take "as is". Extension field-names beginning with "X-" will not be defined as a standard field. MDN field names not beginning with "X- " need to be registered with the Internet Assigned Numbers Authority (IANA) and described in an RFC. The X-Received-MIC field described in this document will be registered with IANA. 3.1.9 Internet draft (dusse): S/MIME Message Specification [8] This specification describes how MIME shall carry PKCS7 signature and envelope information. 3.2 Vocabulary The email address of the receiving organization's EDI processing system. The email address of the sending organi- zation's EDI processing system. Transmission date "EDIFACT" or "EDI-X12" or "EDI-consent" "Quoted-printable" or "Base64" ANSI X12 or EDIFACT EDI Interchange, or mutually agreed electronic commerce file "us-ascii" or "iso-8859-1" (note that if iso-8859-1 is used, in most cases encoding will be required "Quoted printable" or "Base 64" "md5" or "sha1" -Key ID of recipient's public key -Session key (symmetric) -Timestamp -Key ID of sender's public key -Leading two octets of message digest -Message digest -Filename -Timestamp -contentType = EnvelopedData -version = Version -recipientInfos = RecipientInfos -contentType = Data -contentEncryptionAlgorithm = ContentEncryptionAlgorithmIdentifier -encryptedContent = -ContentType = SignedData -version = Version -digestAlgorithms = DigestAlgorithmIdentifiers -contentType = Data -content = -signerInfos = SignerInfo NOTE: The examples below are just that - examples. They are provided for illustration purposes only. Refer to the RFCs or drafts under "7. References" for the actual grammar and protocol definitions. 3.3 Structure of an EDI MIME message - No encryption/No signature To: Subject: From: Date: Mime-Version: 1.0 Content-Type: Application/ Content-Transfer-Encoding: 3.4 Structure of an EDI MIME message - S/MIME 3.4.1 S/MIME Overview S/MIME or the Secure/Multipurpose Internet Mail Extensions, specify formats and procedures when the cryptographic security services of authentication, message integrity, non-repudiation of origin, and confidentiality are applied to Internet MIME messages. S/MIME is specified in draft draft-dusse-mime-msg-spec-00.txt, and an S/MIME implementation guide is available from RSA Data Securities, Inc. This applicability statement sets forth the implementation requirements and recommendations needed to use S/MIME when sending EDI on the Internet. These implementation requirements and recommendations are intended to ensure a base level of inter- operability among S/MIME EDI implementations. NOTE: The S/MIME Implementation Guide, Version 2 specifies a restricted profile for use for export purposes and an unrestricted profile for use domestically. These profiles specify the cryptographic algorithms and key lengths that a conformant S/MIME implementation must support. It is recommended that for Internet EDI, these profiles be adhered to. However, cryptographic algorithms, and key lengths are parameters that need to be set by the trading partnership, and can vary from what is specified by the S/MIME standards. Content Types: signedAndEnvelopedData content type should not be used when sending EDI on the Internet. Objections have been raised concerning the fact that the issuerAndSerialNumber for each signer of a signedAndEnvelopedData content is left in the clear. This information could be used to derive the identity of the signer of the message. The use of signedAndEnvelopedData also precludes the ability to sign information that is in addition to, but separate from the primary signed contents. The use of the S/MIME "authenticated attributes" is not required for Internet EDI, since it is generally sufficient to sign the EDI MIME content. The S/MIME Implementation Guide, Version 2 requires a compliant S/MIME agent to support the nesting of a signed message format within an enveloped message, for both incoming and outgoing messages. This EDI AS#1 specification also requires the support of a nested signed message within an enveloped message. Therefore, when using S/MIME for the purpose of sending EDI on the Internet, a two step process will be used: the user agent first creates an application/x-pkcs7-mime signed message, and uses this message as input to the creation of an application/x-pkcs7-mime enveloped message. The receiver of an incoming enveloped message that is decrypted and found to contain a signed application/x-pkcs-7-mime type, should process the signed contents and present the signature status and corresponding "data" content to message disposition notification processing -- if a request for a message disposition notification has been made -- otherwise the "data" content is passed to a general MIME processor. The "data" content type is used as the content within the signedData and the envelopedData content types, to indicate the MIME message content which has had security services applied to it. For the purpose of Internet EDI, this "data" content type will contain RFC 1767 specified MIME EDI content, or a MIME multipart content that has a RFC 1767 MIME EDI content as part of the multipart content. Signed Message Type: The S/MIME specification requires support of the signedData content format, and recommends support of the multipart/signed format. For use in Internet EDI, support is required for the signedData content format if message authentication, integrity, and non-repudiation of origin are required. The great value for support of the multipart/signed format is the ability of non- S/MIME-enabled agents to process the content of the body that was signed. The multipart/signed format is recommended when a signed message is being sent to a set of recipients, not all of which are known to have S/MIME enabled agents. Since trading partners using S/MIME to transact EDI on the Internet will by definition have S/MIME- enabled agents, the multipart/signed loses much of its utility. Support of the multipart/signed format for use in Internet EDI is therefore optional. 3.4.2 Example: S/MIME - Signature Only To: Subject: From: Date: Mime-Version: 1.0 Content-Type: application/x-pkcs7-mime Content-Transfer-Encoding: base64 &Mime-Version: 1.0 &Content-Type: Application/; &Content-Transfer-Encoding: & & Notes: -The lines preceded with "&" is what the signature is calculated over - consists of (refer to: PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.): ContentType = SignedData version = Version digestAlgorithms = DigestAlgorithmIdentifiers contentType = Data content = NOTE: that except for ContentType and Content, the actual object identifiers or values for the fields are not specified. (See PKCS#9 and the S/MIME Implementation Guide, Version 2 from RSA Labs, Inc., for these object identifiers.) - consists of (refer to: PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.): signerInfos = SignerInfo NOTE: The signerInfo contains the digestAlgorithm, the digestEncryptionAlgorithm, and the encryptedDigest or the digital signature. The issuerAndSerialNumber field defined within the signerInfos identifies a signing trading partner's public-key certificate. Since Internet EDI allows self-certification, this field can contain the distinguished name of the sending trading partner for the issuer distinguished name. 3.4.3 Example: S/MIME - Encryption Only To: Subject: From: Date: Mime-Version: 1.0 Content-Type: application/x-pkcs7-mime Content-Transfer-Encoding: base64 &Mime-Version: 1.0 &Content-Type: Application/; &Content-Transfer-Encoding: & & Notes: -The text preceded by "&" indicates that it is really encrypted, but presented as text for clarity - consists of (See PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.): contentType = EnvelopedData version = Version recipientInfos = RecipientInfos contentType = Data contentEncryptionAlgorithm = ContentEncryptionAlgorithmIdentifier encryptedContent = NOTE: Except for contentType, the actual object identifiers or values for the fields are not specified. (See PKCS#9 and the S/MIME Implementation Guide, Version 2 from RSA Labs, Inc., for these objects.) NOTE: The recipientInfos contains the symmetric encryption key encrypted with the receiver's public key. The issuerAndSerialNumber field defined within the recipientInfos identifies a receiving trading partner's public-key certificate. Since Internet EDI allows self-certification, this field can contain the distinguished name of the receiving trading partner for the issuer distinguished name. NOTE: In general there will be one recipientInfos specified, but in the case of RFQs there may be n recipientInfos specified. 3.4.4 Example: S/MIME - Signature and Encryption The required support for EDI Internet is to first create an application/x-pkcs7-mime signedData message, and then to create an application/x-pkcs7-mime envelopedData message with the application/x- pkcs7-mime signedData message as input to the application/x-pkcs7-mime envelopedData message. To: Subject: From: Date: Mime-Version: 1.0 Content-Type: application/x-pkcs7-mime Content-Transfer-Encoding: base64 *Mime-Version: 1.0 *Content-Type: application/x-pkcs7-mime * *&MIME-Version: 1.0 *&Content-Type: Application/; *&Content-Transfer-Encoding: *& * Notes: - The lines preceded with "&" is what the signature is calculated over. - The text preceded by "*" indicates that it is really encrypted, but presented as text for clarity - consists of (See PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.): contentType = EnvelopedData version = Version recipientInfos = RecipientInfos contentType = Data contentEncryptionAlgorithm = ContentEncryptionAlgorithmIdentifier encryptedContent = NOTE: Except for contentType, the actual object identifiers or values for the fields are not specified. (See PKCS#9 and the S/MIME Implementation Guide, Version 2 from RSA Labs, Inc., for these objects.) NOTE: The recipientInfos contains the symmetric encryption key encrypted with the receiver's public key. The issuerAndSerialNumber field defined within the recipientInfos identifies a receiving trading partner's public-key certificate. Since Internet EDI allows self-certification, this field can contain the distinguished name of the receiving trading partner for the issuer distinguished name. NOTE: In general there will be one recipientInfos specified, but in the case of RFQs there may be n recipientInfos specified. - consists of (refer to: PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.): signerInfos = SignerInfo NOTE: The signerInfo contains the digestAlgorithm, the digestEncryptionAlgorithm, and the encryptedDigest or the digital signature. The issuerAndSerialNumber field defined within the signerInfos identifies a signing trading partner's public-key certificate. Since Internet EDI allows self-certification, this field can contain the distinguished name of the sending trading partner for the issuer distinguished name. 3.5 Structure of an EDI MIME message - PGP/MIME 3.5.1 Overview PGP provides two functional services, signature and encryption, but in reality performs 5 functions in order to do it effectively. 1) Digital signature (MD5, RSA) 2) Compression (ZIP) 3) Message Encryption (IDEA) 4) ASCII Armor 5) Message segmentation When sending a message, the services are performed in that order. With the exception of item 5), these services are optional, meaning a user can choose whether to use signature, encryption, compression and ASCII armor, but commonly, 2) and 4) are always used, while 1) and 3) are used in three ways: 1) Signature only, in which case ASCII armor can be applied only to the signature block to keep the message legible. 2) Encryption only 3) Both signature and encryption Applicability of PGP/MIME and RFC 2015, for use in internet EDI dictates the following: - When both encryption and signature feature is used, the EDI data is first signed, then encrypted in a two-step process, as described in the example. -Compression and ASCII Armor is optional and could be user configurable. The following examples describe use of PGP/MIME without compression and ASCII armor, since those services are managed by PGP, and are optional per this draft . 3.5.2 Example: PGP/MIME - Signature Only To: Subject: From: Date: Mime-Version: 1.0 Content-Type: multipart/signed; boundary="separator"; micalg=pgp-; protocol="application/pgp-signature" --separator &Content-Type: Application/ &Content-Transfer-Encoding: & & --separator Content-Type: application/pgp-signature -----BEGIN PGP MESSAGE----- Version 2.6.2 fgfjhHjhJhgljhgJGHGJHGJHJHJhghjhJHJuytIYTiutTYT34553//YRytdhfFFQere /876JHJHGIUIUgsdIUYgYTRdgggguytUTIUlbXssfdsfdREWrewREWREEWE88POF/DF frtFFKFG+GFff= =ndaj -----END PGP MESSAGE----- --separator-- Notes: -The lines preceded with "&" is what the signature is calculated over. 3.5.3 Example: PGP/MIME - Encryption Only To: Subject: From: Date: Mime-Version: 1.0 Content-Type: multipart/encrypted; boundary="separator"; protocol="application/pgp-encrypted" --separator Content-Type: application/pgp-encrypted Version: 1 --separator Content-Type: application/octet-stream -----BEGIN PGP MESSAGE----- Version 2.6.2 & &Content-Type: Application/; &Content-Transfer-Encoding: & & -----END PGP MESSAGE----- --separator-- Notes: -The text preceded by "&" indicates that it is really encrypted, but presented as text for clarity -"pgp control information" contains the following, but refer to PGP specifications or tool kits for details: -Key ID of recipient's public key -Session key (symmetric) -Timestamp -Key ID of sender's public key -Leading two octets of message digest -Message digest -Filename -Timestamp 3.5.4 Example: PGP/MIME - Signature and Encryption The sequence here is that the EDI data is first signed as a multipart/signature body, and then the data plus the signature is encrypted to form the final multipart/encrypted body. Here goes: To: Subject: From: Date: Mime-Version: 1.0 Content-Type: multipart/encrypted; boundary="separator"; protocol="application/pgp-encrypted" --separator Content-Type: application/pgp-encrypted Version: 1 --separator Content-Type: application/octet-stream -----BEGIN PGP MESSAGE----- Version 2.6.2 * * Content-Type: multipart/signed; boundary="signed separator"; * micalg=pgp-; protocol="application/pgp-signature" * * --signed separator * &Content-Type: Application/ * &Content-Transfer-Encoding: * & * & * * --signed separator * Content-Type: application/pgp-signature * * -----BEGIN PGP MESSAGE----- * Version 2.6.2 * * fgfjhHjhJhgljhgJGHGJHGJHJHJhghjhJHJuytIYTiutTYT34553//YRytd * /GIUIUgsIUYgYTRdgggguytUTIUlbXssfdsfdREWrewREWREEWE88POF/DF * frtFFKFG+GFff= * =ndaj * -----END PGP MESSAGE----- * * --signed separator-- -----END PGP MESSAGE----- --separator-- Notes: - The lines preceded with "&" is what the signature is calculated over. - The text preceded by "*" indicates that it is really encrypted, but presented as text for clarity - "pgp control information" contains the following, but refer to PGP specifications or tool kits for details: -Key ID of recipient's public key -Session key (symmetric) -Timestamp -Key ID of sender's public key -Leading two octets of message digest -Message digest -Filename -Timestamp -RFC 2015 allows another way to handle the above in a combined fashion, However, for the purpose of EDI we require the above method, which is based on MIME Security Multiparts [4] RFC 1847. This method performs signature and encryption in a two-step process, first signing the data, then encrypting it. This is also consistent with PGP's recommendations. 4. Receipts 4.1 Introduction In order to provide a non-repudiation of receipt (NRR) or signed receipt, a message disposition notification (MDN) as specified by draft- ietf-receipt-mdn-01 is to be implemented by a receiving trading partner's UA (User Agent). The message disposition notification is then digitally signed and returned to the sending trading partner as part of a multipart/signed content. The required support for signed receipts when doing EDI Internet is as follows: 1). Create a multipart/report; report-type=disposition-notification. 2). Calculate the MIC on the message disposition notification. 3). Digitally sign the MIC. 4). Create a multipart/signed content with the message disposition notification as the first body part, and the signed MIC calculated on the message disposition notification as the second body part. 5). Return the signed receipt to the sending trading partner. The MDN is used to notify a sending trading partner that sent a signed, or signed and encrypted EDI Interchange that: 1). The receiving trading partner acknowledges receipt of the sent EDI Interchange. 2). The receiving trading partner has authenticated the sender of the EDI Interchange. 3). The receiving trading partner has verified the integrity of the received EDI Interchange. Regardless of whether the EDI Interchange was sent in S/MIME or PGP/MIME format, the receiving trading partner's UA must provide the following basic processing: 1). If the sent EDI Interchange is encrypted, then the encrypted symmetric key and initialization vector (if applicable) is decrypted using the receiver's private key. 2). The decrypted symmetric encryption key is then used to decrypt the EDI Interchange. 3). The receiving trading partner authenticates signatures in a message using the sender's public key. The authentication algorithm performs the following: a). The message integrity check (MIC or Message Digest) contained within the signature is decrypted using the sender's public key. b). A MIC on the signed contents (the MIME header and encoded EDI object, as per RFC1767) in the message received is calculated using the same one-way hash function that the sending trading partner used. c). The MIC extracted from the signature is compared with the MIC calculated using the same one-way hash function that the sending trading partner used. 4). The receiving trading partner formats the MDN and sets the calculated MIC into the MDN extension field. 5). The receiving trading partner creates a multipart/signed MIME message according to RFC 1847. 6). The MDN is the first part of the multipart/signed message, and the digital signature is created over this MDN, including its MIME headers. 7). The second part of the multipart/signed message contains the digital signature. The "protocol" option specified in the multipart/signed is as follows: S/MIME: protocol = "application/pkcs-7-mime" PGP/MIME: protocol = "application/pgp-signature" The EDI Interchange and the RFC 1767 MIME EDI content header, can actually be part of a multi-part MIME content-type. When the EDI Interchange is part of a multi-part MIME content-type, the MIC is calculated across the entire multi-part content, including the MIME headers. The multi-part MIME content that contains the EDI Interchange is then enveloped in either PKCS #7 or PGP format. The signed MDN, when received by the sender of the EDI Interchange can then be used by the sender: 1). As an acknowledgment that the EDI Interchange sent, was delivered and acknowledged by the receiving trading partner. The receiver does this by returning the original message id of the sent message in the signed MDN. 2). As an acknowledgment that the integrity of the EDI Interchange was verified by the receiving trading partner. The receiver does this by returning the calculated MIC of the received EDI Interchange (and 1767 MIME headers) in the X-Received-MIC field of the signed MDN. 3). As an acknowledgment that the receiving trading partner has authenticated the sender of the EDI Interchange. 4). As a non-repudiation of receipt when the signed MIC calculated over the MDN, is successfully decrypted by the sender with the receiver's public key. 4.2 Requesting a signed receipt Message Disposition Notifications are requested as per the draft-ietf- receipt-mdn-01.txt. A request that the receiving user agent issue a message disposition notification is made by placing the following header into the message to be sent: mdn-request-header = "Disposition-notification-to" ":" address The address field is specified as an RFC 822 user@domain address, and is the return address for the message disposition notification. A note to implementors: this RFC does not preclude the sending of a signed receipt whenever EDI content is received by a trading partner. The sending of a signed receipt can be made a configurable parameter, and a signed receipt may be returned even though the original message does not contain a receipt request. 4.3 Message Disposition Notification Format The format of a message disposition notification is as specified in draft-ietf-receipt-mdn-01.txt. For use in EDI over the Internet the following format will be used: - content-type - per RFC1892 and the ietf-receipt-mdn specification - reporting-ua-field - per ietf-receipt-mdn specification - mdn-gateway-field - per ietf-receipt-mdn specification - original-recipient-field - per ietf-receipt-mdn specification - final-recipient-field - per ietf-receipt-mdn specification - original-message-id-field - per ietf-receipt-mdn specification - disposition-field - for EDI use: * autoprocessed - when the received content(s) are successfully processed * decryption_failed - when the receiver could not decrypt the contents * authentication_failed - when the receiver could not authenticate the sender * integrity_check_failed - when the receiver could not verify content integrity - extension field - the following extension field will be added in order to support signed-receipts for RFC 1767 specified content types and multi-part specified content types which includes RFC 1767 content types. The extension field is sent only when the received contents are successfully processed. - extension field = "X-" "Received-MIC" ":" MIC MIC or message integrity check, is defined as the result of a one-way hash function applied to the received EDI Interchange and RFC 1767 MIME content type information, or the multi-part MIME content containing RFC 1767 MIME EDI content information. The MIC is also referred to as a message digest when using the MD5 one-way hash function. 4.4 Message Disposition Notification Processing 4.4.1 Large File Processing Large EDI Interchanges sent via SMTP can be automatically fragmented by some message transfer agents. A subtype of message, "partial", is defined in RFC 1521 to allow large objects to be delivered as separate pieces of mail and to be automatically reassembled by the receiving user agent. Using message, "partial", can help alleviate fragmentation of large messages by different message transfer agents, but does not completely eliminate the problem. It is still possible that a piece of a partial message, upon re-assembly, may prove to contain a partial message as well. This is allowed by the Internet standards, and it is the responsibility of the user agent to re-assemble the fragmented pieces. It is recommended that the size of the EDI Interchange sent via SMTP be configurable so that if fragmentation does occur, then message, "partial" can be used to send the large EDI Interchange in smaller pieces. RFC 1521 defines the use of Content-Type: message/partial. Support of the message/partial content type for use in Internet EDI is optional. The receiving UA is required to re-assemble the original message before sending the message disposition notification to the original sender of the message. A message disposition notification is used to specify the disposition of the entire message that was sent, and should not be returned by a processing UA until the entire message is received, even if the received message requires re-assembling. In general, EDI content compresses well, since there is repetitive data in most EDI Interchanges. Instead of implementing the message/partial, compression of the EDI Interchange can be done after the signature is applied to the EDI Interchange, and before encryption. When no signature applied, then compression is applied before the encryption. Compression is an alternative solution to implementing Content-Type: message/partial when sending large EDI Interchanges on the Internet. Applying compression before encryption strengthens cryptographic security since repetitious strings are reduced. This sequence is consistent with the PGP sequence as well. 4.4.3 Example The following is an example of a signed receipt returned by a UA after processing a MIME EDI content type that was signed. NOTE: This example is provided as an illustration only, and is not considered part of the protocol specification. If an example conflicts with the protocol definitions specified above or in the other referenced RFCs, the example is wrong. To: Subject: From: Date: Mime-Version: 1.0 Content-Type: multipart/signed; boundary="separator"; micalg=rsa-md5; protocol="application/x-pkcs7-mime" --separator &Content-Type: multipart/report; report-type=disposition & notification; boundary = "xxxxx" & &--xxxxx & The message sent to Edi Recipient & has been received, the EDI Interchange was succesfully & decrypted and its integrity was verified. In addition, the & sender of the message, Edi Sender & was authenticated as the originator of the message. There is & no guarantee however that the EDI Interchange was & syntactically correct, or was received by the EDI & application. & &--xxxxx & Content-Type: message/disposition-notification & & Reporting-UA: good-edi-internet-ua.edicorp.com (ediua 1.0) & Original-Recipient: rfc822; Edi_Recipient@edicorp.com & Final-Recipient: rfc822; Edi_Recipient@edicorp.com & Original-Message-ID: <17759920005.12345@edicorp.com> & Disposition: autoprocessed & X-Received-MIC: Q2hlY2sgSW50XwdyaXRIQ…… & &--xxxxx & Content-Type: message/rfc822 & &--xxxxx-- --separator Content-Type: application/x-pkcs7-mime @ContentType = SignedData @version = Version @digestAlgorithms = DigestAlgorithmIdentifiers @contentType = Data @content = fgfjhHjhJhgljhgJGHGJHGJHJHJhghjhJHJuytIYTiutTYT34553//YRytdhfFFQere /876JHJHGIUIUgsdIUYgYTRdgggguytUTIUlbXssfdsfdREWrewREWREEWE88POF/DF frtFFKFG+GFff= =ndaj @signerInfos = SignerInfo --separator-- Notes: -The lines preceeded with "&" is what the signature is calculated over. -The text preceeded by "@" indicates PKCS#7 defined fields and types. (See PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.) As specified by RFC 1892, returning the original message is not necessary. This is an optional body part. It is recommended that the received headers be placed in the third body part, as it can be helpful in tracking problems. 5. Public key certificate handling 5.1 Near term approach In the near term, the exchange of public keys and certificaition of these keys must be handled as part of the process of establishing a trading partnership. The UA and/or EDI application interface must maintain a database of public keys used for encryption or signatures, in addition to the mapping between EDI trading partner ID and RFC822 email address. The procedures for establishing a trading partnership and configuring the secure EDI messaging system might vary among trading partners and software packages. For systems which make use of X.509 certificates, it is recommended that trading partners self-certify each other if an agreed upon certification authority is not used. It is highly recommended that when trading partners are using S/MIME, that they also exchange public key certificates using the recommendations specified in the S/MIME Implementation Guide Version 2. The message formats and S/MIME conformance requirements for certificate exchange are specified in this document. This applicability statement does NOT require the use of a certification authority. 5.2 Long term approach In the long term, additional Internet-EDI standards may be developed to simplify the process of establishing a trading partnership, including the third party authentication of trading partners, as well as attributes of the trading relationship. 6. Authors' Addresses Mats Jansson mjansson@agathon.com LiNK 1026 Wilmington Way Redwood City, CA 94062 USA Chuck Shih chucks@actracorp.com Actra Corp. 610 East Caribbean Drive Sunnyvale, CA 94089 USA Nancy Turaj nturaj@.mitre.org MITRE Corporation Mailstop: W657 1820 Dolley Madison Blvd. McLean, VA 22102-3481 USA Rik Drummond drummond@onramp.com The Drummond Group 5008 Bentwood Ct. Ft. Worth, TX 76132 USA 7. References [1] N. Borenstein, N.Freed, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, September 23, 1993. [2] D. Crocker, "MIME Encapsulation of EDI Objects", RFC 1767, March 2, 1995. [3] D. Crocker, "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, August 13, 1982. [4] M. Elkins, "MIME Security With Pretty Good Privacy (PGP)", RFC 2015, Sept. 1996. [5] R. Fajman, "An Extensible Message Format for Message Disposition Notifications", draft-ietf-receipt-mdn-01.txt, May 13, 1996. [6] J. Galvin, S. Murphy, S. Crocker, N. Freed, "Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted", RFC 1847, Oct. 3,1995 [7] J. Postel, "Simple Mail Transfer Protocol", STD 10, RFC 821, August 1, 1982. [8] S. Dusse, "S/MIME Message Specification; PKCS Security Services for MIME", Internet draft: draft-dusse-mime-msg-spec 00.txt [9] C. Shih, "Requirements for Inter-operable Internet EDI", July 1996. [10] G. Vaudreuil, "The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages", RFC 1892, January 15, 1996.