Network Working Group T. Harding
Request for Comments: 3335 Cyclone Commerce
Category: Standards Track R. Drummond
Drummond Group
C. Shih
Gartner Group
September 2002
MIME-based Secure Peer-to-Peer
Business Data Interchange over the Internet
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document describes how to exchange structured business data
securely using SMTP transport for Electronic Data Interchange, (EDI -
either the American Standards Committee X12 or UN/EDIFACT, Electronic
Data Interchange for Administration, Commerce and Transport), XML or
other data used for business to business data interchange. The data
is packaged using standard MIME content-types. Authentication and
privacy are obtained by using Cryptographic Message Syntax (S/MIME)
or OpenPGP security body parts. Authenticated acknowledgements make
use of multipart/signed replies to the original SMTP message.
Harding, et. al. Standards Track [Page 1]
RFC 3335 MIME-based Secure EDI September 2002 Table of Contents 1.0 Introduction .................................................3 2.0 Overview .....................................................4 2.1 Purpose of a Security Guideline for MIME EDI .................4 2.2 Definitions ..................................................4 2.2.1 Terms ........................................................4 2.2.2 The Secure Transmission Loop .................................5 2.2.3 Definition of Receipts .......................................5 2.3 Assumptions ..................................................6 2.3.1 EDI Process Assumptions ......................................6 2.3.2 Flexibility Assumptions ......................................7 3.0 Referenced RFCs and Their Contribution .......................8 3.1 RFC 821 SMTP [7] .............................................8 3.2 RFC 822 Text Message Format [3] ..............................8 3.3 RFC 1847 MIME Security Multiparts [6] ........................8 3.4 RFC 1892 Multipart/Report [9] ................................8 3.5 RFC 1767 EDI Content [2] .....................................9 3.6 RFC 2015, 3156, 2440 PGP/MIME [4] ............................9 3.7 RFC 2045, 2046, and 2049 MIME [1] ............................9 3.8 RFC 2298 Message Disposition Notification [5] ................9 3.9 RFC 2633 and 2630 S/MIME Version 3 Message Specifications [8] 9 4.0 Structure of an EDI MIME Message - Applicability .............9 4.1 Introduction .................................................9 4.2 Structure of an EDI MIME Message - PGP/MIME .................10 4.2.1 No Encryption, No Signature .................................10 4.2.2 No Encryption, Signature ....................................10 4.2.3 Encryption, No Signature ....................................10 4.2.4 Encryption, Signature .......................................10 4.3 Structure of an EDI MIME Message - S/MIME ...................10 4.3.1 No encryption, No Signature..................................10 4.3.2 No encryption, Signature ....................................10 4.3.3 Encryption, No Signature ....................................11 4.3.4 Encryption, Signature .......................................11 5.0 Receipts ....................................................11 5.1 Introduction ................................................11 5.2 Requesting a Signed Receipt .................................13 5.2.1 Additional Signed Receipt Considerations ....................16 5.3 Message Disposition Notification Format .....................17 5.3.1 Message Disposition Notification Extensions .................18 5.3.2 Disposition Mode, Type, and Modifier Use ....................19 5.4 Message Disposition Notification Processing .................21 5.4.1 Large File Processing .......................................21 5.4.2 Example .....................................................22 6.0 Public Key Certificate Handling .............................24 6.1 Near Term Approach ..........................................24 6.2 Long Term Approach ..........................................24 7.0 Security Considerations .....................................25 Harding, et. al. Standards Track [Page 2]
RFC 3335 MIME-based Secure EDI September 2002 8.0 Acknowledgments .............................................26 9.0 References ..................................................26 Appendix IANA Registration Form ...................................28 Authors' Addresses ................................................28 Full Copyright Statement ..........................................29 1.0 Introduction Previous work on Internet EDI focused on specifying MIME content types for EDI data ([2] RFC 1767). This document 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 document also recognizes contemporary RFCs and is attempting to "re-invent" as little as possible. While this document focuses specifically on EDI data, any other data type is also supported. With an enhancement in the area of "receipts", as described below (5.2), secure Internet MIME based EDI can be accomplished by using and complying with the following RFCs: -RFC 821 SMTP -RFC 822 Text Message Formats -RFC 1767 EDI Content Type -RFC 1847 Security Multiparts for MIME -RFC 1892 Multipart/Report -RFC 2015, 3156, 2440 MIME/PGP -RFC 2045 to 2049 MIME RFCs -RFC 2298 Message Disposition Notification -RFC 2630, 2633 S/MIME v3 Specification Our intent here is to define clearly and precisely how these are used together, and what is required by user agents to be compliant with this document. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. Harding, et. al. Standards Track [Page 3]
RFC 3335 MIME-based Secure EDI September 2002 2.0 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 document 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 Internet messaging format used to Notification convey a receipt. This term is used interchangeably with receipt. A signed MDN is a signed receipt. Non-repudiation of NRR is a "legal event" that occurs when Receipt (NRR) the 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 format and protocol for adding Cryptographic signature and/or encryption services to Internet MIME messages. Harding, et. al. Standards Track [Page 4]
RFC 3335 MIME-based Secure EDI September 2002 2.2.2 The secure transmission loop 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 environment. 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 signs and encrypts the data using either PGP/MIME or S/MIME. In addition, the message will request a signed receipt to be returned to the sender of the message. -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 returns a signed receipt to the sending organization in the form of a message disposition notification message. This signed receipt will contain the hash of the signature from the received message, indicating to the sender that the received message was verified and/or decrypted properly. 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 security features with their 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 resulting in a receipt which is NOT signed. The second term is used if the acknowledgment is for an interchange resulting in a receipt which IS signed. The method used to request a receipt or a signed receipt is defined in RFC 2298, "An Extensible Message Format for Message Disposition Notifications". The "rule" is: - If a receipt is requested, explicitly specifying that the receipt be signed, then the receipt MUST be returned with a signature. Harding, et. al. Standards Track [Page 5]
RFC 3335 MIME-based Secure EDI September 2002 - If a receipt is requested, explicitly specifying that the receipt be signed, but the recipient cannot support the requested protocol format or requested MIC algorithms, then a receipt, either signed or unsigned SHOULD be returned. - If a signature is not explicitly requested, or if the signed receipt request parameter is not recognized by the UA, a receipt may or may not be returned. This behavior is consistent with the MDN RFC 2298. 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 signed receipt coming back from recipient of the message. 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 services. 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 routing from existing commercial EDI networks (called Value Added Networks or VANs) to the Internet, 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 this. -X12.58 and UN/EDIFACT security considerations The most common EDI standards bodies, 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. Harding, et. al. Standards Track [Page 6]
RFC 3335 MIME-based Secure EDI September 2002 2.3.2 Flexibility Assumptions -Encrypted or unencrypted data This specification allows for EDI message exchange where the EDI data can either be un-protected or protected by means of encryption. -Signed or unsigned data This specification allows for EDI message exchange with or without digital signature of the original EDI transmission. -Use of receipt or not This specification allows for EDI message transmission with or without a request for receipt notification. If a signed receipt notification is requested however, a mic value is REQUIRED as part of the returned receipt, unless an error condition occurs in which a mic value cannot be returned. In error cases, an un-signed receipt or MDN SHOULD be returned with the correct "disposition modifier" error value. -Formatting choices This specification defines the 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 RFC 2015/3156/2440, as reflected in [4] "MIME Security with Pretty Good Privacy" (PGP); OpenPGP Message Format, and RFC 2633/2630 [8] "S/MIME Version 3 Message Specification; Cryptographic Message Syntax". PGP/MIME or S/MIME as defined in this Applicability statement. -Hash function, message digest choices When a signature is used, it is RECOMMENDED that the SHA1 hash algorithm be used for all outgoing messages, and that both MD5 and SHA1 be supported for incoming messages. In summary, the following eight permutations are possible in any given trading relationship: (1) Sender sends unencrypted data, does NOT request a receipt. Harding, et. al. Standards Track [Page 7]
RFC 3335 MIME-based Secure EDI September 2002 (2) Sender sends unencrypted data, requests a signed or unsigned receipt. The receiver sends back the signed or unsigned receipt. (3) Sender sends encrypted data, does NOT request a receipt. (4) Sender sends encrypted data, requests a signed or unsigned receipt. The receiver sends back the signed or unsigned receipt. (5) Sender sends signed data, does NOT request a signed or unsigned receipt. (6) Sender sends signed data, requests a signed or unsigned receipt. Receiver sends back the signed or unsigned receipt. (7) Sender sends encrypted and signed data, does NOT request a signed or unsigned receipt. (8) Sender sends encrypted and signed data, requests a signed or unsigned receipt. Receiver sends back the signed or unsigned receipt. NOTE: Users can choose any of the eight possibilities, but only example (8), when a signed receipt is requested, offers the whole suite of security features described in the "Secure transmission loop" above. 3.0 Referenced RFCs and Their Contribution 3.1 RFC 821 SMTP [7] This is the core mail transfer standard that all MTAs need to adhere to. 3.2 RFC 822 Text Message Format [3] Defines message header fields and the parts making up a message. 3.3 RFC 1847 MIME Security Multiparts [6] This document defines security multiparts for MIME: multipart/encrypted and multipart/signed. 3.4 RFC 1892 Multipart/report [9] This RFC defines the use of the multipart/report content type, something that the MDN RFC 2298 builds upon. Harding, et. al. Standards Track [Page 8]
RFC 3335 MIME-based Secure EDI September 2002 3.5 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). 3.6 RFC 2015, 3156, 2440 PGP/MIME [4] These RFCs define the use of content types "multipart/encrypted", "multipart/signed", "application/pgp encrypted" and "application/pgp-signature" for defining MIME PGP content. 3.7 RFC 2045, 2046, and 2049 MIME [1] These are the basic MIME standards, upon which all MIME related RFCs build, including this one. Key contributions include definition of "content type", "sub-type" and "multipart", as well as encoding guidelines, which establishes 7-bit US-ASCII as the canonical character set to be used in Internet messaging. 3.8 RFC 2298 Message Disposition Notification [5] This Internet RFC defines how a message disposition notification (MDN) is requested, and the format and syntax of the MDN. The MDN is the basis upon which receipts and signed receipts are defined in this specification. 3.9 RFC 2633 and 2630 S/MIME Version 3 Message Specifications [8] This specification describes how MIME shall carry CMS Objects. 4.0 Structure of an EDI MIME Message - Applicability 4.1 Introduction The structures below are described hierarchically in terms of which RFC's are applied to form the specific structure. For details of how to code in compliance with all RFC's involved, turn directly to the RFC's referenced. Also, these structures describe the initial transmission only. Receipts, and requests for receipts are handled in section 5. Harding, et. al. Standards Track [Page 9]
RFC 3335 MIME-based Secure EDI September 2002 4.2 Structure of an EDI MIME Message - PGP/MIME 4.2.1 No Encryption, No Signature -RFC822/2045 -RFC1767 (application/EDIxxxx or /xml) 4.2.2 No Encryption, Signature -RFC822/2045 -RFC1847 (multipart/signed) -RFC1767 (application/EDIxxxx or /xml) -RFC2015/2440/3156 (application/pgp-signature) 4.2.3 Encryption, No Signature -RFC822/2045 -RFC1847 (multipart/encrypted) -RFC2015/2440/3156 (application/pgp-encrypted) -"Version: 1" -RFC2015/2440/3156 (application/octet-stream) -RFC1767 (application/EDIxxxx or /xml) (encrypted) 4.2.4 Encryption, Signature -RFC822/2045 -RFC1847 (multipart/encrypted) -RFC2015/2440/3156 (application/pgp-encrypted) -"Version: 1" -RFC2015/2440/3156 (application/octet-stream) -RFC1847 (multipart/signed)(encrypted) -RFC1767 (application/EDIxxxx or /xml)(encrypted) -RFC2015/2440/3156 (application/pgp-signature)(encrypted) 4.3 Structure of an EDI MIME Message - S/MIME 4.3.1 No Encryption, No Signature -RFC822/2045 -RFC1767 (application/EDIxxxx or /xml) 4.3.2 No Encryption, Signature -RFC822/2045 -RFC1847 (multipart/signed) -RFC1767 (application/EDIxxxx or /xml) -RFC2633 (application/pkcs7-signature) Harding, et. al. Standards Track [Page 10]
RFC 3335 MIME-based Secure EDI September 2002 4.3.3 Encryption, No Signature -RFC822/2045 -RFC2633 (application/pkcs7-mime) -RFC1767 (application/EDIxxxx or /xml) (encrypted) 4.3.4 Encryption, Signature -RFC822/2045 -RFC2633 (application/pkcs7-mime) -RFC1847 (multipart/signed) (encrypted) -RFC1767 (application/EDIxxxx or /xml) (encrypted) -RFC2633 (application/pkcs7-signature) (encrypted) 5.0 Receipts 5.1 Introduction In order to support non-repudiation of receipt (NRR), a signed receipt, based on digitally signing a message disposition notification, is to be implemented by a receiving trading partner's UA (User Agent). The message disposition notification, specified by RFC 2298 is digitally signed by a receiving trading partner as part of a multipart/signed MIME message. The following support for signed receipts is REQUIRED: 1) The ability to create a multipart/report; where the report-type = disposition-notification. 2) The ability to calculate a message integrity check (MIC) on the received message. The calculated MIC value will be returned to the sender of the message inside the signed receipt. 4) The ability to create a multipart/signed content with the message disposition notification as the first body part, and the signature as the second body part. 5) The ability to return the signed receipt to the sending trading partner. The signed receipt is used to notify a sending trading partner that requested the signed receipt that: 1) The receiving trading partner acknowledges receipt of the sent EDI Interchange. Harding, et. al. Standards Track [Page 11]
RFC 3335 MIME-based Secure EDI September 2002 2) If the sent message was signed, then the receiving trading partner has authenticated the sender of the EDI Interchange. 3) If the sent message was signed, then the receiving trading partner has verified the integrity of the sent 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), is decrypted using the sender's public key. b) A MIC on the signed contents (the MIME header and encoded EDI object, as per RFC 1767) 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 message that was sent, and the MIC calculated using the same one-way hash function that the sending trading partner used is compared for equality. 4) The receiving trading partner formats the MDN and sets the calculated MIC into the "Received-content-MIC" 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. Harding, et. al. Standards Track [Page 12]
RFC 3335 MIME-based Secure EDI September 2002 7) The second part of the multipart/signed message contains the digital signature. The "protocol" option specified in the second part of the multipart/signed is as follows: S/MIME: protocol = "application/pkcs-7-signature" PGP/MIME: protocol = "application/pgp-signature" 8) The signature information is formatted according to S/MIME or PGP/MIME specifications. 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 MUST be calculated across the entire multi-part content, including the MIME headers. The signed MDN, when received by the sender of the EDI Interchange can 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 MDN portion of the signed receipt. 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 "Received-content-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 MDN is successfully verified by the sender with the receiving trading partner's public key and the returned mic value inside the MDN is the same as the digest of the original message. 5.2 Requesting a Signed Receipt Message Disposition Notifications are requested as per RFC 2298, "An Extensible Message Format for Message Disposition Notification". 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: Harding, et. al. Standards Track [Page 13]
RFC 3335 MIME-based Secure EDI September 2002 MDN-request-header = "Disposition-notification-to" ":" mail-address The mail-address field is specified as an RFC 822 user@domain address, and is the return address for the message disposition notification. In addition to requesting a message disposition notification, a message disposition notification that is digitally signed, or what has been referred to as a signed receipt, can be requested by placing the following in the message header following the "Disposition- Notification-To" line. Disposition-notification-options = "Disposition-Notification-Options" ":" disposition-notification-parameters where disposition-notification-parameters = parameter *(";" parameter) where parameter = attribute "=" importance ", " 1#value" where importance = "required" | "optional" So the Disposition-notification-options string could be: signed-receipt-protocol=optional, <protocol symbol>; signed-receipt-micalg=optional, <micalg1>, <micalg2>,...; The currently supported values for <protocol symbol> are "pkcs7-signature", for the S/MIME detached signature format, or "pgp-signature", for the pgp signature format. The currently supported values for MIC algorithm values are: Algorithm Value used MD5 md5 SHA-1 sha1 Harding, et. al. Standards Track [Page 14]
RFC 3335 MIME-based Secure EDI September 2002 (Historical Note: Some early implementations of EDIINT emitted and expected "rsa-md5" and "rsa-sha1" for the micalg parameter.) Receiving agents SHOULD be able to recover gracefully from a micalg parameter value that they do not recognize. An example of a formatted options line would be as follows: Disposition-notification-options: signed-receipt-protocol=optional, pkcs7-signature; signed-receipt-micalg=optional, sha1, md5 The semantics of the "signed-receipt-protocol" parameter is as follows: 1) The "signed-receipt-protocol" parameter is used to request a signed receipt from the recipient trading partner. The "signed-receipt-protocol" parameter also specifies the format in which the signed receipt should be returned to the requester. The "signed-receipt-micalg" parameter is a list of MIC algorithms preferred by the requester for use in signing the returned receipt. The list of MIC algorithms should be honored by the recipient from left to right. Both the "signed-receipt-protocol" and the "signed-receipt-micalg" option parameters are REQUIRED when requesting a signed receipt. 2) The "importance" attribute of "Optional" is defined in the MDN RFC 2298 and has the following meaning: Parameters with an importance of "Optional" permit a UA that does not understand the particular options parameter to still generate a MDN in response to a request for a MDN. A UA that does not understand the "signed-receipt-protocol" parameter, or the "signed-receipt-micalg" will obviously not return a signed receipt. The importance of "Optional" is used for the signed receipt parameters because it is RECOMMENDED that an MDN be returned to the requesting trading partner even if the recipient could not sign it. The returned MDN will contain information on the disposition of the message as well as why the MDN could not be signed. See the Disposition field in section 5.3 for more information. Harding, et. al. Standards Track [Page 15]
RFC 3335 MIME-based Secure EDI September 2002 Within an EDI trading relationship, if a signed receipt is expected and is not returned, then the validity of the transaction is up to the trading partners to resolve. In general, if a signed receipt is required in the trading relationship and is not received, the transaction will likely not be considered valid. 5.2.1 Additional Signed Receipt Considerations The "rules" stated in Section 2.2.3 for signed receipts are as follows: 1) When a receipt is requested, explicitly specifying that the receipt be signed, then the receipt MUST be returned with a signature. 2) When a receipt is requested, explicitly specifying that the receipt be signed, but the recipient cannot support either the requested protocol format, or requested MIC algorithms, then either a signed or unsigned receipt SHOULD be returned. 3) When a signature is not explicitly requested, or if the signed receipt request parameter is not recognized by the UA, then no receipt, an unsigned receipt, or a signed receipt MAY be returned by the recipient. NOTE: For Internet EDI, it is RECOMMENDED that when a signature is not explicitly requested, or if parameters are not recognized, that the UA send back at a minimum, an unsigned receipt. If a signed receipt however was always returned as a policy, whether requested or not, then any false unsigned receipts can be repudiated. When a request for a signed receipt is made, but there is an error in processing the contents of the message, a signed receipt MUST still be returned. The request for a signed receipt SHALL still be honored, though the transaction itself may not be valid. The reason for why the contents could not be processed MUST be set in the "disposition-field". When a request for a signed receipt is made, the "Received-content-MIC" MUST always be returned to the requester. The"Received-content-MIC" MUST be calculated as follows: - For any signed messages, the MIC to be returned is calculated on the RFC1767 MIME header and content. Canonicalization as specified in RFC 1848 MUST be performed before the MIC is calculated, since the sender requesting the signed receipt was also REQUIRED to canonicalize. Harding, et. al. Standards Track [Page 16]
RFC 3335 MIME-based Secure EDI September 2002 - For encrypted, unsigned messages, the MIC to be returned is calculated on the decrypted RFC 1767 MIME header and content. The content after decryption MUST be canonicalized before the MIC is calculated. - For unsigned, unencrypted messages, the MIC MUST be calculated over the message contents prior to Content-Transfer-Encoding and without the MIME or any other RFC 822 headers, since these are sometimes altered or reordered by MTAs. 5.3 Message Disposition Notification Format The format of a message disposition notification is specified in RFC 2298. For use in Internet EDI, the following format will be used: - content-type - per RFC 1892 and the RFC 2298 specification - reporting-ua-field - per RFC 2298 specification - MDN-gateway-field - per RFC 2298 specification - original-recipient-field - per RFC 2298 specification - final-recipient-field - per RFC 2298 specification - original-message-id-field - per RFC 2298 specification - disposition-field - the following "disposition-mode" values SHOULD be used for Internet EDI: "automatic-action" - The disposition described by the disposition type was a result of an automatic action, rather than an explicit instruction by the user for this message. "manual-action" - The disposition described by the disposition type was a result of an explicit instruction by the user rather than some sort of automatically performed action. "MDN-sent-automatically" - The MDN was sent because the UA had previously been configured to do so. "MDN-sent-manually" - The user explicitly gave permission for this particular MDN to be sent. "MDN-sent-manually" is meaningful with "manual-action", but not with "automatic-action". Harding, et. al. Standards Track [Page 17]
RFC 3335 MIME-based Secure EDI September 2002 - disposition-field - the following "disposition-type" values SHOULD be used for Internet EDI: "processed" - The message has been processed in some manner (e.g., printed, faxed, forwarded, gatewayed) without being displayed to the user. The user may or may not see the message later. "failed" - A failure occurred that prevented the proper generation of an MDN. More information about the cause of the failure may be contained in a Failure field. The "failed" disposition type is not to be used for the situation in which there is some problem in processing the message other than interpreting the request for an MDN. The "processed" or other disposition type with appropriate disposition modifiers is to be used in such situations. - disposition-field - the following "disposition-modifier" values SHOULD be used for Internet EDI: "error" - An error of some sort occurred that prevented successful processing of the message. Further information is contained in an Error field. "warning" - The message was successfully processed but some sort of exceptional condition occurred. Further Information is contained in a Warning field. 5.3.1 Message Disposition Notification Extensions The following "extension field" will be added in order to support signed receipts for RFC 1767 MIME content type and multipart MIME content types that include the RFC 1767 MIME content type. The extension field" defined below follows the "disposition-field" in the MDN. The "Received-content-MIC" extension field is set when the integrity of the received message is verified. The MIC is the base64 encoded quantity computed over the received message with a hash function. For details of "what" the "Received-content-MIC" should be calculated over, see Section 5.2.1. The algorithm used to calculate the "Received-content-MIC" value MUST be the same as the "micalg" value used by the sender in the multipart/signed message. When no signature is received, or the mic-alg parameter is not supported then it is RECOMMENDED that the SHA1 algorithm be used to calculate the MIC on the received message or message contents. Harding, et. al. Standards Track [Page 18]
RFC 3335 MIME-based Secure EDI September 2002 This field is set only when the contents of the message are processed successfully. This field is used in conjunction with the recipient's signature on the MDN in order for the sender to verify "non- repudiation of receipt". - extension field = "Received-content-MIC" ":" MIC where: <MIC> = <base64MicValue> "," <micalg> <base64MicValue> = the result of one way hash function, base64 encoded. < micalg> = the micalg value defined in RFC1847, an IANA registered MIC algorithm ID token. 5.3.2 Disposition Mode, Type, and Modifier Use Guidelines for use of the "disposition-mode", "disposition-type", and "disposition-modifier" fields within Internet EDI are discussed in this section. The "disposition-mode", "disposition-type', and "disposition-modifier' fields are described in detail in RFC 2298. The "disposition-mode', "disposition-type" and "disposition-modifier" values SHOULD be used as follows: 5.3.2.1 Successful Processing When the request for a receipt or signed receipt, and the received message contents are successfully processed by the receiving EDI UA, a receipt or MDN SHOULD be returned with the "disposition-type" set to there is no explicit way for a user to control the sending of the MDN, then the first part of the "disposition-mode" should be set to "automatic-action". When the MDN is being sent under user configurable control, then the first part of the "disposition-mode" should be set to "manual-action". Since a request for a signed receipt should always be honored, the user MUST not be allowed to configure the UA to not send a signed receipt when the sender requests one. The second part of the "disposition-mode" is set to "MDN-sent- manually" if the user gave explicit permission for the MDN to be sent. Again, the user MUST not be allowed to explicitly refuse to send a signed receipt when the sender requests one. The second part of the "disposition-mode" is set to "MDN-sent-automatically" whenever the EDI UA sends the MDN automatically, regardless of whether the sending was under a user's, administrator's, or under software control. Harding, et. al. Standards Track [Page 19]
RFC 3335 MIME-based Secure EDI September 2002 Since EDI content is generally handled automatically by the EDI UA, a request for a receipt or signed receipt will generally return the following in the "disposition-field": Disposition: automatic-action/MDN-sent-automatically; processed Note this specification does not restrict the use of the "disposition-mode" to just automatic actions. Manual actions are valid as long as it is kept in mind that a request for a signed receipt MUST be honored. 5.3.2.2 Unprocessed Content The request for a signed receipt requires the use of two "disposition-notification-options", which specify the protocol format of the returned signed receipt, and the MIC algorithm used to calculate the mic over the message contents. The "disposition-field" values that should be used in the case where the message content is being rejected or ignored, for instance if the EDI UA determines that a signed receipt cannot be returned because it does not support the requested protocol format, so the EDI UA chooses not to process the message contents itself, should be specified in the MDN "disposition-field" as follows: Disposition: "disposition-mode"; failed/Failure: unsupported format The syntax of the "failed" "disposition-type" is general, allowing the sending of any textual information along with the "failed" "disposition-type". For use in Internet EDI, the following "failed" values are defined: "Failure: unsupported format" "Failure: unsupported MIC-algorithms" 5.3.2.3 Content Processing Errors When errors occur processing the received message content, the "disposition-field" should be set to the "processed" "disposition- type" value and the "error" "disposition-modifier" value. For use in Internet EDI, the following "error" "disposition-modifier" values are defined: "Error: decryption-failed" - the receiver could not decrypt the message contents. "Error: authentication-failed" - the receiver could not authenticate the sender. Harding, et. al. Standards Track [Page 20]
RFC 3335 MIME-based Secure EDI September 2002 "Error: integrity-check-failed" - the receiver could not verify content integrity. "Error: unexpected-processing-error" - a catch-all for any additional processing errors. An example of how the "disposition-field" would look when content processing errors are detected is as follows: Disposition: "disposition-mode"; processed/Error: decryption-failed 5.3.2.4 Content Processing Warnings Situations arise in EDI where even if a trading partner cannot be authenticated correctly, the trading partners still agree to continue processing the EDI transactions. Transaction reconciliation is done between the trading partners at a later time. In the content processing warning situations as described above, the "disposition- field" SHOULD be set to the "processed" "disposition-type" value, and the "warning" "disposition-modifier" value. For use in Internet EDI, the following "warning" "disposition-modifier" values are defined: "Warning: authentication-failed, processing continued" An example of how the "disposition-field" would look when content processing warnings are detected is as follows: Disposition: "disposition-mode"; processed/Warning: authentication-failed, processing continued 5.4 Message Disposition Notification Processing 5.4.1 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 2045 [1] 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 reassemble the fragmented pieces. Harding, et. al. Standards Track [Page 21]
RFC 3335 MIME-based Secure EDI September 2002 It is RECOMMENDED that the size of the EDI Interchange sent via SMTP be configurable so that if fragmentation is needed, then message/partial can be used to send the large EDI Interchange in smaller pieces. RFC 2045 [1] defines the use of Content-Type: message/partial. Note: Support of the message/partial content type for use in Internet EDI is OPTIONAL and in the absence of knowledge that the recipient supports partial it SHOULD NOT be used. 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. 5.4.2 Example The following is an example of a signed receipt returned by a UA after successfully processing a MIME EDI content type. The sending trading partner has requested a return signed receipt. This example follows the S/MIME application/pkcs-7-signature format. 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: <recipient email> Subject: From: <sender email> Date: <date> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="separator"; micalg=sha1; protocol="application/pkcs7-signature" --separator & Content-Type: multipart/report; report-type=disposition & notification; boundary="xxxxx" & & --xxxxx & Content-Type: text/plain & & The message sent to Recipient <Recipient@cyclonesoftware.com> & has been received, the EDI Interchange was successfully & decrypted and its integrity was verified. In addition, the Harding, et. al. Standards Track [Page 22]
RFC 3335 MIME-based Secure EDI September 2002 & sender of the message, Sender <Edi_Sender@cyclonesoftware.com> & 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: Interchange.cyclonesoftware.com (CI 2.2) & Original-Recipient: rfc822; Edi_Recipient@cyclonesoftware.com & Final-Recipient: rfc822; Edi_Recipient@cyclonesoftware.com & Original-Message-ID: <17759920005.12345@cyclonesoftware.com > & Disposition: automatic-action/MDN-sent-automatically; processed & Received-content-MIC: Q2hlY2sgSW50XwdyaXRIQ, sha1 & & --xxxxx & Content-Type: message/rfc822 & & To: <recipient email> & Subject: & & [additional header fields go here] & & --xxxxx-- --separator Content-Type: application/pkcs7-signature; name=smime.p7s; Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename=smime.p7s MIIHygYJKoZIhvcNAQcDoIIHuzCCB7cCAQAxgfIwge8CAQAwg ZgwgYMxFjAUBgNVBAMTDVRlcnJ5IEhhcmRpbmcxEDAOBgNVBA oTB0NZQ0xPTkUxDDAKBgNVBAsTA04vQTEQMA4GA1UEBxMHU= --separator-- Notes: -The lines preceded with "&" is what the signature is calculated over. (For details on how to prepare the multipart/signed with protocol = "application/pkcs7-signature" see the "S/MIME Message Specification, PKCS Security Services for MIME".) Harding, et. al. Standards Track [Page 23]
RFC 3335 MIME-based Secure EDI September 2002 Note: As specified by RFC 1892 [9], returning the original or portions of the original message in the third body part of the multipart/report is not required. This is an optional body part. It is RECOMMENDED that the received headers from the original message be placed in the third body part, as they can be helpful in tracking problems. Also note that the textual first body part of the multipart/report can be used to include a more detailed explanation of the error conditions reported by the disposition headers. The first body part of the multipart/report when used in this way, allows a person to better diagnose a problem in detail. 6.0 Public Key Certificate Handling 6.1 Near Term Approach In the near term, the exchange of public keys and certification 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 RFC 822 [3] 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 Version 3 Message Specification. 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. The use of a certification authority is therefore OPTIONAL. 6.2 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. Harding, et. al. Standards Track [Page 24]
RFC 3335 MIME-based Secure EDI September 2002 7.0 Security Considerations This entire document is concerned with secure transport of business to business data, and considers both privacy and authentication issues. Extracted from S/MIME Version 2 Message Specification: 40-bit encryption is considered weak by most cryptographers. Using weak cryptography offers little actual security over sending plain text. However, other features of S/MIME, such as the specification of tripleDES or AES and the ability to announce stronger cryptographic capabilities to parties with whom you communicate, allow senders to create messages that use strong encryption. Using weak cryptography is never recommended unless the only alternative is no cryptography. When feasible, sending and receiving agents should inform senders and recipients the relative cryptographic strength of messages. Extracted from S/MIME Version 2 Certificate Handling: When processing certificates, there are many situations where the processing might fail. Because the processing may be done by a user agent, a security gateway, or other program, there is no single way to handle such failures. Just because the methods to handle the failures has not been listed, however, the reader should not assume that they are not important. The opposite is true: if a certificate is not provably valid and associated with the message, the processing software should take immediate and noticeable steps to inform the end user about it. Some of the many places where signature and certificate checking might fail include: - no certificate chain leads to a trusted CA - no ability to check the CRL for a certificate - an invalid CRL was received - the CRL being checked is expired - the certificate is expired - the certificate has been revoked There are certainly other instances where a certificate may be invalid, and it is the responsibility of the processing software to check them all thoroughly, and to decide what to do if the check fails. Harding, et. al. Standards Track [Page 25]
RFC 3335 MIME-based Secure EDI September 2002 8.0 Acknowledgments Many thanks go out to the previous authors of the MIME-based Secure EDI IETF Draft: Mats Jansson. The authors would like to extend special thanks to Carl Hage, Jun Ding, Dale Moberg, and Karen Rosenthal for providing the team with valuable, and very thorough feedback. Without participants like those cited above, these efforts become hard to complete in a way useful to the users and implementers of the technology. In addition, the authors would like to thank Harald Alvestrand, Jim Galvin, and Roger Fajman for their guidance and input. 9.0 References [1] Borenstein, N. and N. Freed, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. Borenstein, N. and N. Freed, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. Borenstein, N. and N. Freed, "Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples", RFC 2049, November 1996. [2] Crocker, D., "MIME Encapsulation of EDI Objects", RFC 1767, March 1995. [3] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [4] Elkins, M., "MIME Security With Pretty Good Privacy (PGP)", RFC 2015, October 1996. Callas, J., Donnerhacke, L., Finney, H. and R.Thayer "OpenPGP Message Format", RFC 2440, November 1998. Elkins, M., Del Torto, D., Levien, R. and T. Roessler "MIME Security with OpenPGP", RFC 3156, August 2001. [5] Fajman, R., "An Extensible Message Format for Message Disposition Notifications", RFC 2298, March 1998. [6] Galvin, J., Murphy, S., Crocker, S. and N. Freed, "Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted", RFC 1847, October 1995. Harding, et. al. Standards Track [Page 26]
RFC 3335 MIME-based Secure EDI September 2002 [7] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April 1982. [8] Ramsdell, B., "S/MIME Version 3 Message Specification; Cryptographic Message Syntax", RFC 2633, June 1999. Housley, R., "Cryptographic Message Syntax", RFC 2630, June 1999. [9] Vaudreuil, G., "The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages", RFC 1892, January 1996. Harding, et. al. Standards Track [Page 27]
RFC 3335 MIME-based Secure EDI September 2002 Appendix IANA Registration Form A.1 IANA registration of the signed-receipt-protocol content disposition parameter Parameter-name: signed-receipt-protocol Syntax: See section 5.2 of this document Specification: See section 5.2 of this document A.2 IANA registration of the signed-receipt-micalg content disposition parameter Parameter-name: signed-receipt-micalg Syntax: See section 5.2 of this document Specification: See section 5.2 of this document A.3 IANA registration of the Received-content-MIC MDN extension field name Extension field name: Received-content-MIC Syntax: See section 5.3.1 of this document Specification: See section 5.3.1 of this document Authors' Addresses Terry Harding Cyclone Commerce 8388 E. Hartford Drive Scottsdale, Arizona 85255, USA EMail: tharding@cyclonecommerce.com Chuck Shih Gartner Group 251 River Oaks Parkway San Jose, CA 95134-1913 USA EMail: chuck.shih@gartner.com Rik Drummond Drummond Group P.O. Box 101567 Ft. Worth, TX 76105 USA EMail: rik@drummondgroup.com Harding, et. al. Standards Track [Page 28]
RFC 3335 MIME-based Secure EDI September 2002
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Harding, et. al. Standards Track [Page 29]
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