EDIINT Working Group Dale Moberg Internet draft Rik Drummond Expires: July 2003 January 2003 HTTP Transport for Secure Peer-to-Peer Business Data Interchange over the Internet draft-ietf-ediint-as2-12.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsolete by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Any questions, comments, and reports of defects or ambiguities in this specification may be sent to the mailing list for the EDIINT working group of the IETF, using the address . Requests to subscribe to the mailing list should be addressed to . Copyright Notice Copyright (c) The Internet Society (2002). All rights reserved. NOTE FROM WG LEADER: This draft has been extensively rewritten from draft-ietf-ediint-as2-11.txt to enhance clarity. The previous draft attempted to combine two means of accomplishing the objectives which made the draft very clumbersom and greatly contributed to the lack of clarity. This draft extends the AS1 functionality to HTTP, drops PGP and gib?? In the event that gib?? is still required as and ietf standard i recommend we do it as AS3. Moberg, Drummond, [page 1] HTTP Transport for Secure EDI Jan 2003 Abstract This document describes how to exchange structured business data securely using HTTP transfer for XML, Binary, Electronic Data Interchange, (EDI - either the American Standards Committee X12 or UN/EDIFACT, Electronic Data Interchange for Administration, Commerce and Transport) or other data describable in MIME 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) security body parts. Authenticated acknowledgements make use of multipart/signed repliesto the original HTTP message. Feedback Instructions: NOTE TO RFC EDITOR: This section should be removed by the RFC editor prior to publication. If you want to provide feedback on this draft, follow these guidelines: -Send feedback via e-mail to the ietf-ediint list for discussion, with "AS#2" in the Subject field. To enter or follow the discussion, you need to subscribe to ietf-ediint@imc.org. -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. Table of Contents 1. Introduction 2. Overview 2.1 Overall operations 2.2 Purpose of a security guideline for MIME EDI 2.3 Definitions 2.4 Assumptions 2.4.1 EDI process assumptions 2.4.2 Flexibility assumptions 3. Referenced RFCs 3.1 RFC 2616 HTTP v1.1 Moberg, Drummond, [page 2] HTTP Transport for Secure EDI Jan 2003 3.2 RFC 1847 MIME Security Multiparts 3.3 RFC 1892 Multipart/report 3.4 RFC 1767 EDI Content 3.5 RFC 2045, 2046, 2049 MIME 3.6 RFC 2298 Message Disposition Notification 3.7 RFC 2633, 2630 S/MIME Version 3 Message Specifications 3.8 RFC 2376 XML Media Types 4. Structure of an AS2 message 4.1 Introduction 4.2 Structure of EDI MIME message 5. HTTP Considerations 5.1 Sending EDI in HTTP Post Requests 5.2 Unused MIME headers and operations 5.2.1 Content-Transfer-Encoding not used 5.2.2 Epilogue must be empty 5.2.3 Lengthy message bodies 5.3 Modification of MIME or other headers or parameters used 5.3.1 Content-Length 5.3.2 Final Recipient and Original Recipient 5.3.3 Message-Id and Original-Message-Id 5.3.4 Host Header 5.4 HTTP Response Status Codes 5.5 HTTP Error Recovery 6. AS2 Headers 6.1 AS2 Version Header 6.2 AS2 System Identifiers 7. Structure and Processing of an MDN Message 7.1 Introduction 7.2 Synchronous and Asynchronous MDNs 7.3 Requesting a signed receipt 7.3.1 Signed receipt considerations 7.4 MDN Format 7.4.1 AS2-MDN General Formats 7.4.2 AS2-MDN Construction 7.4.3 AS2-MDN Fields 7.4.4 Additional AS2-MDN Programming Notes 7.5 Disposition Mode, Type, and Modifier 7.5.1 Disposition Mode Overview 7.5.2 Successful Processing Status Indications 7.5.3 Unsuccessful Processed Content 7.5.4 Unsuccessful Non-Content Processing 7.5.5 Processing Warnings 7.5.6 Backwards Compatibility with Disposition Type, Modifier, and Extension 7.6 Receipt Reply Considerations in a HTTP Post 8. Public key certificate handling 9. Security Considerations 10. Acknowledgements 11. References 12. Authors' Addresses Appendix A. Message Examples B. IANA Registration Form Moberg, Drummond [page 3] HTTP Transport for Secure EDI Jan 2003 1. Introduction Previous work on Internet EDI focused on specifying MIME content types for EDI data [2] and extending this work to support secure EC/EDI transport over SMTP [4]. This document expands on RFC 1767 to specify a comprehensive set of data security features, specifically data privacy, dataintegrity/authenticity, non-repudiation of origin and non-repudiation of receipt over HTTP. This document also recognizes contemporary RFCs and is attempting to "re-invent" as little as possible. While this document focuses on EDI data, any other data type describable in a MIME format are also supported. Internet MIME based EDI can be accomplished by using and complying with the following RFC's : * -RFC 2616 Hyper Text Transfer Protocol * -RFC 1767 EDI Content Type * -RFC 2376 XML Media Types * -RFC 1847 Security Multiparts for MIME * -RFC 1892 Multipart/Report * -RFC 2045 to 2049 MIME RFC's * -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. 2. Overview 2.1 Overall Operations A HTTP POST operation [3] is used to send appropriately packaged EDI, XML, or other business data. The Request-URI ([3], section 9.5) identifies a process to unpack and handle the message data and to generate a reply for the client that contains a message disposition acknowledgement or a multipart/report, signed or unsigned, and possibly other turnaround transactions. This request/reply transactional interchange provides secure, reliable, and authenticated transport for EDI or other business data using HTTP. The security protocols and structures used also support auditable records of these transmissions, acknowledgements, and authentication. 2.2 Purpose of a security guideline for MIME EDI The purpose of these specifications is to ensure interoperability between B2B Electronic Commerce 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. 2.3 Definitions 2.3.1. Terms * EDI - Electronic Data Interchange * EC - Business to Business Electronic Commerce * B2B - Business to Business * Receipt - The functional message that is sent from a receiver to a Moberg, Drummond, [page 4] HTTP Transport for Secure EDI Jan 2003 sender to acknowledge receipt of an EDI/EC interchange. This message may be either synchronous or asynchronous in nature. * Signed Receipt - A receipt with a digital signature. * Synchronous Receipt - A receipt returned to the sender during the same HTTP session as the sender's original message * Asynchronous Receipt - A receipt returned to the sender on a different communication session than the sender's original message session * Message Disposition Notification (MDN) - The Internet messaging format used to convey a receipt. This term is used interchangeably with receipt. A MDN is a receipt. * Non-repudiation of receipt (NRR) - NRR is a "legal event" that occurs when 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. * S/MIME - A format and protocol for adding Cryptographic signature and/or encryption services to Internet MIME messages. * SHA-1 - A secure, one-way hash algorithm used in conjunction with digital signature. This is the recommend algorithm for AS2 * MD5 - A secure, one-way hash algorithm used in conjunction with digital signature. This algorithm is accepted in AS2 but not recommended due to its short key length * MIC - The message integrity check (MIC), also called the message digest, is the digest output of the hash algorithm used by the digital signature. The digital signature is computed over the MIC. * User Agent (UA) - The application that handles and processes the AS2 request 2.3.2 The secure transmission loop This document's focus is on the formats and protocols for exchanging EDI/EC content that has had security applied to it using the Internet's HTTP environment. The "secure transmission loop" for EDI/EC involves one organization sending a signed and encrypted EDI/EC 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 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. Moberg, Drummond, [page 5] HTTP Transport for Secure EDI Jan 2003 * -The receiving organization then returns a signed receipt, as requested either synchronous or asynchronous, to the sending organization in the form of a message disposition notification. 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, will satisfy all security requirements and implement non-repudiation of receipt for the exchange. 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. 2.3.3 Definition of receipts The term used for both the functional activity and the message for acknowledging delivery of an EDI/EC interchange is receipt or signed receipt. The 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. A term often used in combination with receipts is non-repudiation of receipt. 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. For information on how to format and process receipts in AS2, refer to section 7. 2.4 Assumptions 2.4.1 EDI/EC process assumptions -Encrypted object is an EDI/EC Interchange This specification assumes that a typical EDI/EC interchange is the lowest level object that will be subject to security services. Specifically, in EDI 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/EC 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. 2.4.2 Flexibility assumptions -Encrypted or un-encrypted data This specification allows for EDI/EC message exchange where the Moberg, Drummond, [page 6] HTTP Transport for Secure EDI Jan 2003 EDI/EC data can either be un-protected or protected by means of encryption. -Signed or unsigned data This specification allows for EDI/EC message exchange with or without digital signature of the original EDI transmission. -Use of receipt or not This specification allows for EDI/EC 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 unsigned receipt or MDN SHOULD be returned with the correct "disposition modifier" error value. -Use of synchronous or asynchronous receipts This specification allows in addition to a receipt request the specification of the type of receipt that should be returned. It supports synchronous or asynchronous receipts in the MDN format specified in section 7 of this document. -Security Formatting This specification relies on the guidelines set forth in RFC 2633/2630 [8] "S/MIME Version 3 Message Specification; Cryptographic Message Syntax". 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 utgoing messages, and that both MD5 and SHA1 be supported for incoming messages. -Permutation Summary In summary, the following twelve security permutations are possible in any given trading relationship: 1. Sender sends un-encrypted data, does NOT request a receipt. 2. Sender sends un-encrypted data, requests an unsigned receipt. The receiver sends back the unsigned receipt. 3. Sender sends un-encrypted data, requests a signed receipt. The receiver sends back the signed receipt. 4. Sender sends encrypted data, does NOT request a receipt. 5. Sender sends encrypted data, requests an unsigned receipt. The receiver sends back the unsigned receipt. 6. Sender sends encrypted data, requests a signed. The receiver sends back the signed receipt. 7. Sender sends signed data, does NOT request a signed or unsigned receipt. 8. Sender sends signed data, requests an unsigned receipt. Receiver sends back the unsigned receipt. 9. Sender sends signed data, requests a signed receipt. Receiver sends back the signed receipt. Moberg, Drummond, [page 7] HTTP Transport for Secure EDI Jan 2003 10. Sender sends encrypted and signed data, does NOT request a signed or unsigned receipt. 11. Sender sends encrypted and signed data, requests an unsigned receipt. Receiver sends back the unsigned receipt. 12. Sender sends encrypted and signed data, requests a signed receipt. Receiver sends back the signed receipt. NOTE: Users can choose any of the twelve possibilities, but only the last example (12), when a signed receipt is requested, offers the whole suite of security features described in the "Secure transmission loop" above. Additionally, the receipts discussed above may be either synchronous or asynchronous in nature depending on the type requested. The use of either the synchronous or asynchronous receipts does not change the nature of the "Secure transmission loop" in support of NRR. 3. Referenced RFC's and their contribution 3.1 RFC 2616 HTTP v1.1 [3] This document specifies how data is transferred using HTTP. 3.2 RFC 1847 MIME Security Multiparts [6] This document defines security multipart for MIME: multipart/encrypted and multipart/signed. 3.3 RFC 1892 Multipart/report [9] This RFC defines the use of the multipart/report content type, something that the MDN RFC 2298 builds upon. 3.4 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). 3.5 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. 3.6 RFC 2298 Message Disposition Notification [5] This Internet RFC defines how a 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. 3.7 RFC 2633 and 2630 S/MIME Version 3 Message Specifications [8] This specification describes how MIME shall carry Cryptographic Message Syntax (CMS) Objects. 3.8 RFC 2376 XML Media Types [12] This RFC defines the use of content type "application" for XML (application/xml). Moberg, Drummond, [page 8] HTTP Transport for Secure EDI Jan 2003 4. Structure of an AS2 message 4.1 Introduction The basic structure of an AS2 messages consists of MIME format inside an HTTP message with a few additional specific AS2 headers. 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. Any difference between AS2 implantations and RFCs are mentioned specifically in the sections below. 4.2 Structure of an Internet EDI MIME message No encryption, no signature -RFC2616/2045 -RFC1767/RFC2376 (application/EDIxxxx or /xml) No encryption, signature -RFC2616/2045 -RFC1847 (multipart/signed) -RFC1767/RFC2376 (application/EDIxxxx or /xml) -RFC2633 (application/pkcs7-signature) Encryption, no signature -RFC2616/2045 -RFC2633 (application/pkcs7-mime) -RFC1767/RFC2376 (application/EDIxxxx or /xml)(encrypted) Encryption, signature -RFC2616/2045 -RFC2633 (application/pkcs7-mime) -RFC1847 (multipart/signed)(encrypted) -RFC1767/RFC2376 (application/EDIxxxx or /xml)(encrypted) -RFC2633 (application/pkcs7-signature)(encrypted) MDN over HTTP, no signature -RFC2616/2045 -RFC2298 (message/disposition-notification) MDN over HTTP, signature -RFC2616/2045 -RFC1847 (multipart/signed) -RFC2298 (message/disposition-notification) -RFC2633 (application/pkcs7-signature) MDN over SMTP, no signature MDN over SMTP, signature Refer to the EDI over SMTP standard [4]. While all MIME content types SHOULD be supported. The following MIME content types MUST be supported: Content-type: multipart/signed Content-Type: multipart/report Content-type: message/disposition-notification Content-Type: application/PKCS7-signature Content-Type: application/PKCS7-mime Content-Type: application/EDI-X12 Content-Type: application/EDIFACT Moberg, Drummond, [page 9] HTTP Transport for Secure EDI Jan 2003 Content-Type: application/edi-consent Content-Type: application/XML 5. HTTP Considerations 5.1 Sending EDI in HTTP Post Requests The request line will have the form: "POST Request-URI HTTP/1.1", with spaces and followed by a CRLF. The Request-URI is typically exchanged out of band, as part of setting up a bilateral trading partner agreement. Applications should be prepared to deal with an initial reply containing a status indicating a need for authentication of the usual types used for authorizing access to the Request-URI ([3], section 10.4.2 and elsewhere). The request line is followed by entity headers specifying content length ([3] section 14.14) and content type ([3], section 14.18). The Host request header ([3] sections 9 and 14.23) is also included. When using Transport Layer Security [10], the request-URI should indicate the appropriate scheme value, HTTPS. Usually only a multipart/signed message body would be sent using TLS, as encrypted message bodies would be redundant. Encrypted message bodies are not prohibited, however. The receiving AS2 system MAY disconnect from the sending AS2 system before completing the reception of the entire entity if it determines the entity being sent is too large to process. For HTTP version 1.1, TCP persistent connections are the default, ([3] sections 8.1.2, 8.2, and 19.7.1). A number of other differences exist because HTTP does not conform to MIME [1] as used in SMTP transport. Relevant differences are summarized below. 5.2 Unused MIME headers and operations 5.2.1 Content-Transfer-Encoding not used in HTTP transport HTTP can handle binary data and so there is no need to use the Content transfer encodings of MIME [1]. This difference is discussed in [3] section 19.4.4. However, a Content transfer encoding value of binary or 8-bit is permissible but not required. The absence of this header must not result in transaction failure. Content transfer encoding of MIME bodyparts within the AS2 message is also allowed. 5.2.2 Epilogue must be empty In [3] section 3.7.2, it is explicitly noted that multiparts must have null epilogues. In [4], sections 5.4.1, options for large file processing are discussed for SMTP transport. For HTTP, large files should be handled correctly by the TCP layer. However, [3] sections 3.5 and 3.6 discuss some options for compressing or chunking entities to be transferred. [3] section 8.1.2.2 discusses a pipelining option that is useful for segmenting large amounts of data. 5.3 Modification of MIME or other headers or parameters used 5.3.1 Content-Length Because connections are persistent, closing a connection cannot be used to indicate the end of an entity. Therefore, [3] sections 4.4 and 14.14 indicate the need for a Content-Length entity header in a request is a MUST. The only exception to this for AS2 messages is when a one-line, successful, HTTP response is provided. 5.3.2 Final and Original Recipient The final and original recipient values SHOULD be the same value. These values MUST NOT be aliases or mailing lists. 5.3.3 Message-Id and Original-Message-Id Moberg, Drummond, [page 10] HTTP Transport for Secure EDI Jan 2003 Message-Id and Original-Message-Id is formatted as defined in RFC2822: "<" id-left "@" id-right ">" (RFC2822 3.6.4) Message-Id length is a maximum of 998 characters. For maximum backward compatibility, Message-Id length SHOULD be 255 characters or less. Message-Id SHOULD be globally unique, id-right should be something unique to the sending host environment (e.g. a host name).When sending a message, always include the angle brackets. Angle brackets are not part of the Message-Id value. For maximum backward compatibility, when receiving a message, do not check for angle brackets. When creating the Original-Message-Id header in an MDN, always use the exact syntax as received on the original message - don't strip or add angle brackets. 5.3.4 Host header The host request header field must be included in the POST request made when sending business data. This field is to allow one server IP address to service multiple hostnames, and potentially conserve IP addresses. See [3], sections 14.23 and 19.5.1. 5.4 HTTP Response Status Codes The status codes return status concerning HTTP operations. For example, the status code 401, together with the WWW-Authenticate header, is used to challenge the client to repeat the request with an Authorization header. Other explicit status codes are documented in [3], sections 6.1.1 and throughout section 10. For errors in the request-URI, 400 ("Bad Request"), 404 ("Not Found") and similar codes are appropriate status codes. These codes and their semantics are specified by [3]. A careful examination of these codes and their semantics should be made before implementing any retry functionality. Retries should not be made if the error is not transient or if retries are explicitly discouraged. 5.5 HTTP Error Recovery If the HTTP client fails to read the HTTP server response data, the POST operation with identical content, including same Message-ID should be repeated, if the condition is transient. The Message-ID on a POST operation can be reused if and only if all of the content (including the original Date) is identical. Details of the retry process -- including time intervals to pause, number of retries to attempt, timeouts for retrying -- are implementation dependent. These settings are selected as part of the trading partner agreement. Servers should be prepared to receive a POST with a repeated Message-ID. The MIME reply body previously sent should be resent, including the MDN and other MIME parts. 6. Additional AS2 Specific HTTP Headers The following headers are to be included in all AS2 messages and all AS2 MDNs, except for asynchronous MDNs that are sent over SMTP [4] and single line HTTP 1.1 responses (section 5.5). 6.1 AS2 Version Header Moberg, Drummond, [page 11] HTTP Transport for Secure EDI Jan 2003 To promote backward compatibility AS2 includes a version: AS2-Version: 1.0 - is used in all implementations implementing this specification. 1.x will be interpreted as 1.0 by all implementation implemented with the AS2-Version: 1.0 header. That is only the most significant digit is used as the version identifier for those not implementing additional non-AS2 specified functionality. AS2-Version: 1.0 through 1.9 MAY be used All implementations WILL interpret "1.0 through 1.9" as implementing this specification. However implementation MAY extend this specification with additional functionality by specifying versions 1.1 through 1.9. If this mechanism is used the additional functionality WILL be completely transparent to implementations with AS2-Version: 1.0 designation. AS2-Version: 1.1 - Designates those implementation which support Compression as defined by RFC 3274. Receiving systems MUST NOT fail due to the absence of the AS2-Version header. Absence would indicate the message is from an implementation based on a previous version of this specification. 6.2 AS2 System Identifiers To aid the receiving system in identifying the sending system, AS2-From and AS2-To headers are used. AS2-From: < AS2-name > AS2-To: < AS2-name > These AS2 headers contain textual values, as described below, identifying the sender/receiver of a data exchange. Their values may be company specific, such as DUNS number, or it may be simply an identification string agreed upon between the trading partners. AS2-text = "!" / ; printable ASCII characters %d35-91 / ; except double-quote (%d34) %d93-126 ; or backslash (%d92) AS2-qtext = AS2-text / SP ; allow space only in quoted text AS2-quoted-pair = "\" DQUOTE / ; \" or "\" "\" ; \\ AS2-quoted-name = DQUOTE 1*128( AS2-qtext / AS2-quoted-pair) DQUOTE AS2-atomic-name = 1*128AS2-text AS2-name = AS2-atomic-name / AS2-quoted-name The AS2-From header value and the AS2-To header value MUST each be an AS2-name, MUST each be comprised of from 1 to 128 printable ASCII characters and MUST NOT be folded. The value in each of these headers is case-sensitive. The string definitions given above are in ABNF format. The AS2-quoted-name SHOULD be used only if the AS2-name does not conform to AS2-atomic-name. Moberg, Drummond, [page 12] HTTP Transport for Secure EDI Jan 2003 The AS2-To and AS2-From header fields MUST be present in all AS2 messages and AS2 MDN's whether asynchronous or synchronous in nature, except for asynchronous MDNs which are sent using SMTP. The sending system may choose to limit the possible AS2-To/AS2-From textual values but must not exceed them. The receiving system must make no restrictions on the textual values and should handle all possible implementations. However, implementers must be aware that older AS2 products may not adhere to this convention. Trading partner agreements should be made to insure that older products can support the system identifiers that are used. If either the AS2-From or the AS2-To or the combination of both header values is determined to be invalid or unknown by the receiving system, the receiving system MAY respond in one of the following ways, but is not limited to these options: 1. The receiving AS2 system MAY disconnect from the sending AS2 system before completing the reception of the entire entity if it determines the HTTP headers do not represent a valid trading-relationship. 2. The receiving AS2 system MAY return an HTTP response with a response code in the 2xx range, with or without any explanation of the error, even if the sending system requested an MDN. 3. The receiving AS2 system MAY return an unsigned MDN with an explanation of the error, if the sending system requested an MDN. 7. Structure and Processing of an MDN Message 7.1 Introduction In order to support non-repudiation of receipt, a signed receipt, based on digitally signing a message disposition notification, is to be implemented by a receiving trading partner's UA. 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. 3) 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. 4) The ability to return the signed receipt to the sending trading partner. 5) The ability to return either a synchronous or asynchronous receipt as the sending party requests. 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 EC Interchange. 2) If the sent message was signed, then the receiving trading partner has authenticated the sender Moberg, Drummond, [page 13] HTTP Transport for Secure EDI Jan 2003 of the EC Interchange. 3) If the sent message was signed, then the receiving trading partner has verified the integrity of the sent EC Interchange. Regardless of whether the EDI/EC Interchange was sent in S/MIME format or not, the receiving trading partner's UA MUST provides the following basic processing: 1) If the sent EDI/EC 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/EC 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. 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" 8) The signature information is formatted according to S/MIME specifications. The EC 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 EC 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. Moberg, Drummond, [page 14] HTTP Transport for Secure EDI Jan 2003 7.2 Synchronous and Asynchronous MDNs The AS2-MDN exists in two varieties: synchronous and asynchronous. The synchronous AS2-MDN is sent as an HTTP response to an HTTP POST or as an HTTPS response to an HTTPS POST. This form of AS2-MDN is called synchronous because the AS2-MDN is returned to the originator of the POST on the same TCP/IP connection. The asynchronous AS2-MDN is sent on a separate HTTP, HTTPS, or SMTP TCP/IP connection. Logically, the asynchronous AS2-MDN is a response to an AS2 message. However, at the transfer-protocol layer, assuming that no HTTP pipelining is utilized, the asynchronous AS2-MDN is delivered on a unique TCP/IP connection, distinct from that used to deliver the original AS2 message. When handling an asynchronous request, the HTTP response must be sent back before the MDN is processed and sent on the separate connection. When an asynchronous AS2-MDN is requested by the sender of an AS2 message, the synchronous HTTP or HTTPS response returned to the sender prior to terminating the connection MUST be a transfer-layer response indicating the success or failure of the data transfer. The format of such a synchronous response MAY be the same as that response returned when no AS2-MDN is requested. The following diagram illustrates the synchronous versus asynchronous varieties of AS2-MDN delivery: Synchronous AS2-MDN [C] ----( connect )----> [S] [C] -----( send )------> [S] [HTTP Request [AS2-Message]] [C] <---( receive )----- [S] [HTTP Response [AS2-MDN]] Asynchronous AS2-MDN [C] ----( connect )----> [S] [C] -----( send )------> [S] [HTTP Request [AS2-Message]] [C] <---( receive )----- [S] [HTTP Response] [C]*<---( connect )----- [S] [C] <--- ( send )------- [S] [HTTP Request [AS2-MDN]] [C] ----( receive )----> [S] [HTTP Response] * Note: An AS2-MDN may be directed to a different host than that of the sender of the AS2 message and may utilize a different transfer protocol than that used to send the original AS2 message. The advantage of the synchronous MDN is that it can provide the sender of the AS2 Message with a verifiable confirmation of message delivery within a synchronous logic flow. However, if the message is relatively large, the time required to process this message and return an AS2-MDN to the sender on the same TCP/IP connection may exceed the maximum configured time permitted for an IP connection. The advantage of the asynchronous MDN is that it provides for the rapid return of a transfer-layer response from the receiver confirming the receipt of data, therefore not requiring a TCP/IP connection to necessarily remain open for very long. However, this design requires that the asynchronous AS2-MDN contain enough information to uniquely identify the original message so that, when received by the AS2 Message originator, the status of the original AS2 Message can be properly updated based on the contents of the AS2-MDN. Synchronous MDNs and asynchronous HTTP and HTTPS MDNs are handled according to the requirements of this specification. However, asynchronous SMTP MDNs are formatted according the requirements of RFC 3335 [4]. 7.3 Requesting a signed receipt Message Disposition Notifications are requested as per RFC 2298. 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" ":" mail-address Moberg, Drummond, [page 15] HTTP Transport for Secure EDI Jan 2003 This syntax is a residual of the use of MDN's in a SMTP transfer. Since this specification is adjusting the functionality from SMTP to HTTP and retaining as much as possible from the [4] functionality, the mail-address must be present but has no meaning in this specification. The mail-address field is specified as an RFC 2822 local-part@domain [addr-spec] address, and while it MUST be present, it MUST NOT be used in any manner in products. Lack of the appropriate syntax WILL BE ignored by the receiving application. In addition to requesting a message disposition notification, an asynchronous message disposition notification can be requested by placing the following header into the message to be sent: Receipt-Delivery-Option: return-url For requesting MDN based receipts, the originator supplies the syntax of extension headers that precede the message body. The header "tags" are as follows: A Disposition-notification-to header is added to indicate that a message disposition notification is requested in the reply to the POST request. This header is specified in [5]. A Message-ID header is added to support message reconciliation, so that an Original-Message-Id value can be returned in the body part of MDN. Other headers, especially "Subject" and "Date", SHOULD be supplied; the values of these headers are often mentioned in the human-readable section of a MDN to aid in identifying the original message. Disposition-notification-options identifies characteristics of message disposition notification in accordance with [5]. EXAMPLE: Disposition-notification-to: xxx@temp.org // Requests the MDN Disposition-notification-options: // The signing options signed-receipt-protocol=optional, pkcs7-signature; // for the MDN signed-receipt-micalg=optional, sha1, md5 Receipt-Delivery-Option: return-url // Requests the MDN // to be asynchronous Disposition-notification-options syntax: 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, ; signed-receipt-micalg=optional, , ,...; The currently supported value for is "pkcs7-signature" for the S/MIME detached signature format. The currently supported values for MIC algorithm values are: Algorithm Value Used -------- ------- MD5 md5 Moberg, Drummond, [page 16] HTTP Transport for Secure EDI Jan 2003 SHA-1 sha1 Receiving agents SHOULD be able to recover gracefully from a parameter value that they do not recognize. Receipt-delivery-option syntax: The "receipt-delivery-option: return-url" string indicates the url to return the asynchronous MDN. This string is NOT present if the receipt is to be synchronous. Because the email value in Disposition-notification-to has no significance for how or where the receipt is transported, the extension header "Receipt-delivery-option" is to be used to provide that information. The receipt-delivery-option's value MUST be a URL indicating the delivery transport destination for the receipt. An example request for an asynchronous MDN via an HTTP transport: Receipt-delivery-option: http://www.AS2system.com An example request for an asynchronous MDN via an HTTP/S transport: Receipt-delivery-option: https://www.AS2system.com An example request for an asynchronous MDN via an SMTP transport: Receipt-delivery-option: mailto:joe@abc.com For more information on requesting SMTP MDNs, refer to RFC 3335 [4]. The semantics of the "signed-receipt-protocol" and the "signed-receipt-micalg" parameters 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. The lack of the presence of the "Receipt-Delivery-Option" indicates a receipt is synchronous in nature. The presence of the "Receipt-Delivery-Option: return-url" indicates that an asynchronous receipt is requested and should be sent to the "return-url". 2) The "importance" attribute of "Optional" is defined in the RFC 2298 section 2.2 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 7.5 for more information. 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. Moberg, Drummond, [page 17] HTTP Transport for Secure EDI Jan 2003 7.3.1 Signed Receipt Considerations 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: 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. - 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-Tranfer-Encoding and without the MIME or any other RFC 822 headers, since these are sometimes altered or reordered by MTAs. 7.4 MDN Format and value This section defines the format of the AS2 Message Disposition Notification (AS2-MDN). 7.4.1 AS2-MDN General Formats The AS2-MDN follows the MDN specification [5] except where noted in this section. The modified entity definitions in this document use the vertical-bar character, '|', to denote a logical "OR" construction. This usage follows RFC 2616 [3]. HTTP entities referred to below are not further defined in this document. Refer to RFC 2616 [3] for complete definitions of HTTP entities. The format of the AS2-MDN is AS2-MDN = AS2-sync-MDN | AS2-async-http-MDN | AS2-async-smtp-MDN AS2-sync-MDN = Status-Line *(( general-header | response-header | entity-header ) CRLF ) CRLF AS2-MDN-body Moberg, Drummond, [page 18] HTTP Transport for Secure EDI Jan 2003 Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF AS2-async-http-MDN = Request-Line *(( general-header | request-header | entity-header ) CRLF ) CRLF AS2-MDN-body Request-Line = Method SP Request-URI SP HTTP-Version CRLF AS2-async-smtp-MDN = *(( general-header | request-header | entity-header ) CRLF ) CRLF AS2-MDN-body AS2-MDN-body = AS2-signed-MDN-body | AS2-unsigned-MDN-body 7.4.2 AS2-MDN Construction The AS2-MDN-body is formatted as a MIME multipart/report with a report-type of "disposition-notification". When unsigned, the transfer-layer ( "outermost" ) entity-headers of the AS2-MDN contain the content-type header that specifies a content-type of "multipart/report" and parameters indicating the report-type, and the value of the outermost multipart boundary. When the AS2-MDN is signed, the transfer-layer ( "outermost" ) entity-headers of the AS2-MDN contain a content-type header that specifies a content-type of "multipart/signed" and parameters indicating the algorithm used to compute the message digest, the signature formatting protocol ( e.g. pkcs7-signature ), and the value of the outermost multipart boundary. The first part of the MIME multipart/signed message is an embedded MIME multipart/report of type "disposition-notification". The second part of the multipart/signed message contains a MIME application/pkcs7-signature message. The first part of the MIME multipart/report is a "human-readable" portion that contains a general description of the message disposition. The second part of the MIME multipart/report is a "machine-readable" portion that is defined as AS2-disposition-notification-content = [ reporting-ua-field CRLF ] [ mdn-gateway-field CRLF ] final-recipient-field CRLF [ original-message-id-field CRLF ] AS2-disposition-field CRLF *( failure-field CRLF ) *( error-field CRLF ) *( warning-field CRLF ) *( extension-field CRLF ) [ AS2-received-content-MIC-field CRLF ] 7.4.3 AS2-MDN Fields The rules for constructing the AS2-disposition-notification-content are identical to the rules for constructing the disposition-notification-content as defined in section 7 of RFC 2298 [5] except that the RFC 2298 disposition-field has been replaced with the AS2-disposition-field and that the AS2-received- -content-MIC field has been added. The differences between the RFC 2298 disposition-field and the AS2-disposition-field are described below. Where there are differences between this document and RFC 2298, those entity Moberg, Drummond, [page 19] HTTP Transport for Secure EDI Jan 2003 names have been changed by prepending "AS2-". Entities below that do not differ from RFC 2298 are not necessarily further defined in this document. Refer to RFC 2298 for AS2-MDN entities that are not further defined in this document. AS2-disposition-field = "Disposition" ":" disposition-mode ";" AS2-disposition-type [ '/' AS2-disposition-modifier ] disposition-mode = action-mode "/" sending-mode action-mode = "manual-action" | "automatic-action" sending-mode = "MDN-sent-manually" | "MDN-sent-automatically" AS2-disposition-type = "processed" | "failed" AS2-disposition-modifier = ( "error" | "warning" ) | AS2-disposition-modifier-extension AS2-disposition-modifier-extension = "error: authentication-failed" | "error: decompression-failed" | "error: decryption-failed" | "error: insufficient-message-security" | "error: integrity-check-failed" | "error: unexpected-processing-error" | "warning: " AS2-MDN-warning-description | "failure: " AS2-MDN-failure-description AS2-MDN-warning-description = *( TEXT ) AS2-MDN-failure-description = *( TEXT ) AS2-received-content-MIC-field = "Received-content-MIC" ":" encoded-message-digest "," digest-alg-id CRLF encoded-message-digest = 1*( 'A'-Z' | 'a'-'z' | '0'-'9' | '/' | '+' | '=' ) ( i.e. base64( message-digest ) ) digest-alg-id = "sha1" | "md5" "Insufficient-message-security" and "decompression-failed" are newer error codes to this specification, are not mentioned in the AS1 RFC, and may not be compatible with earlier implementations of AS2. The "Received-content-MIC" extension field is set when the integrity of the received message is verified. The MIC is the base64-encoded message-digest computed over the received message with a hash function. This field is required for signed receipts but optional for unsigned receipts. For details defining the specific content over which the message-digest is to be computed, see Section 7.3.1 of this document. The algorithm used to calculate the message-digest MUST be the same as the "micalg" value used by the sender in the multipart/signed message. When no signature is received, or the micalg parameter is not provided then the SHA-1 algorithm SHOULD be used to calculate the MIC. This field is set only when Moberg, Drummond, [page 20] HTTP Transport for Secure EDI Jan 2003 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. AS2-MDN field names ( e.g. "Disposition:", "Final-Recipient:") are case-insensitive ( cf. RFC 2298, 3.1.1 ). AS2-MDN action-modes, sending-modes, AS2-disposition-types, and AS2- disposition-modifier values that are defined above, and user-supplied *( TEXT ) values are also case-insensitive. AS2 implementations MUST NOT make assumptions regarding the values supplied for AS2-MDN-warning-description, AS2-MDN-failure- -description nor for the values of any (optional) error, warning, or failure fields. 7.4.4 Additional AS2-MDN Programming Notes 1. Unlike SMTP, for HTTP transactions, Original-Recipient and Final Recipient should not be different. The value in Original-Message-ID SHOULD match the original Message-ID header value. 2. Refer to RFC 2298 for the formatting of the MDN except for the specific deviations mentioned above. 3. Refer to RFC 1892 and RFC 2298 for the formatting of the content-type entity-headers for the MDN. 4. Use an action-mode of "automatic-action" when 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. 5. Use an action-mode of "manual-action" when 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. 6. Use a sending-mode of "MDN-sent-automatically" when the MDN is sent because the UA had previously been configured to do so. 7. Use a sending-mode of "MDN-sent-manually" when the user explicitly gave permission for this particular MDN to be sent. 8. The sending-mode "MDN-sent-manually" is ONLY meaningful with "manual-action", not with "automatic-action". 9. The "failed" disposition type MAY NOT 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. 7.5 Disposition Mode, Type, and Modifier 7.5.1 Disposition Mode Overview This section would provide a brief overview of how processed, error, failure, and warnings are used. 7.5.2 Successful Processing status indication 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 'processed'. When the MDN is sent automatically by the EDI UA, and 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. Moberg, Drummond, [page 21] HTTP Transport for Secure EDI Jan 2003 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. 7.5.3 Unsuccessful processed 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 "failed" AS2-disposition-type should be used when a failure occurs that prevents the proper generation of an MDN. For example, this disposition-type would apply if the sender of the message requested the application of an unsupported message-integrity-check (MIC) algorithm. The "failure:" AS2-disposition-modifier-extension should be used with an implementation-defined description of the failure. Further information about the failure may be contained in a failure-field. The syntax of the "failed" "disposition-type" is general, allowing the sending of any textual information along with the "failed" "disposition-type". Implementations WILL support any printable textual characters after the Failure disposition-type. For use in Internet EDI, the following "failed" values are pre-defined and MUST be supported: "Failure: unsupported format" "Failure: unsupported MIC-algorithms" 7.5.4 Unsuccessful Non-Content Processing When errors occur processing the received message other than content, the "disposition-field" should be set to the "processed" "disposition-type" value and the "error" "disposition-modifier" value. The "error" AS2-disposition-modifier with the "processed" disposition-type should be used to indicate that an error of some sort occurred that prevented successful processing of the message. Further information may be contained in an error-field. An "error:" AS2-disposition-modifier-extension should be used to combine the indication of an error with a pre-defined description of a specific, well-known error. Further information about the error may be contained in an error-field. 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. "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 other than content processing errors are detected is as follows: EXAMPLE Moberg, Drummond, [page 22] HTTP Transport for Secure EDI Jan 2003 Disposition: "disposition-mode"; processed/Error: decryption-failed 7.5.5 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. The "warning" AS2-disposition-modifier should be used with the "processed" disposition-type to indicate that the message was successfully processed but that an exceptional condition occurred. Further information may be contained in a warning-field. A "warning:" AS2-disposition-modifier-extension should be used to combine the indication of a warning with an implementation-defined description of the warning. Further information about the warning may be contained in an warning-field. 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 other than content processing warnings are detected is as follows: EXAMPLE Disposition: "disposition-mode"; processed/Warning: authentication-failed, processing continued 7.5.6 Backwards Compatibility with Disposition Type, Modifier and Extension The following set of examples represent typical constructions of the Disposition field that have been in use by AS2 implementations. This is NOT an exhaustive list of possible constructions. However, AS2 implementations MUST accept constructions of this type to be backward compatible with earlier AS2 versions. Disposition: automatic-action/MDN-sent-automatically; processed Disposition: automatic-action/MDN-sent-automatically; processed/error: authentication-failed Disposition: automatic-action/MDN-sent-automatically; processed/warning: duplicate-document Disposition: automatic-action/MDN-sent-automatically; failed/failure: sender-equals-receiver The following set of examples represent allowable constructions of the Disposition field that combine the historic constructions above with optional RFC 2298 error, warning and failure fields. AS2 implementations MAY produce these constructions. However, AS2 servers are not required to recognize or process optional error, warning, or failure fields at this time. Note that the use of the multiple Error fields in the second example below provides for the indication of multiple error conditions. Disposition: automatic-action/MDN-sent-automatically; processed Disposition: automatic-action/MDN-sent-automatically; processed/error: decryption-failed Error: The signature did not decrypt into a valid PKCS#1 Type-2 block. Error: The length of the decrypted key does not equal the octet-length of the modulus. Disposition: automatic-action/MDN-sent-automatically; processed/warning: duplicate-document Warning: An identical message already exists at the destination server. Disposition: automatic-action/MDN-sent-automatically; failed/failure: Moberg, Drummond, [page 23] HTTP Transport for Secure EDI Jan 2003 sender-equals-receiver Failure: The AS2-To name is identical to the AS2-From name. The following set of examples represent allowable constructions of the Disposition field that employ pure RFC 2298 Disposition-modifiers with optional error, warning and failure fields. These examples are provided as informational only. These constructions are not guaranteed to be backward compatible with AS2 implementations prior to version 1.1. Disposition: automatic-action/MDN-sent-automatically; processed Disposition: automatic-action/MDN-sent-automatically; processed/error Error: authentication-failed Error: The signature did not decrypt into a valid PKCS#1 Type-2 block. Error: The length of the decrypted key does not equal the octet-length of the modulus. Disposition: automatic-action/MDN-sent-automatically; processed/warning Warning: duplicate-document Disposition: automatic-action/MDN-sent-automatically; failed Failure: sender-equals-receiver 7.6 Receipt Reply Considerations in a HTTP POST The details of the response to the POST command vary depending upon whether a receipt has been requested. With no extended header requesting a receipt, and no errors accessing the request-URI specified processing, the status line in the Response to the POST request should be in the 200 range. Status codes in the 200 range should also be used when an entity is returned (a signed receipt in a multipart/signed content type or an unsigned receipt in a multipart/report). Even when the disposition of the data was an error condition at the authentication, decryption or other higher level, the HTTP status code should indicate success at the HTTP level. The HTTP server-side application may respond with an unsolicited multipart/report as a message body that the HTTP client might not have solicited, but this may be discarded by the client. Applications should avoid emitting unsolicited receipt replies because bandwidth or processing limitations might have led administrators to suspend asking for acknowledgements. When a Disposition-Notification-To extension header is present in the POST request entity headers, then entity headers for the MDN should be included. The content type for the MDN receipt (multipart/report [9] or multipart/signed [6]) should be included in the Response entity headers. Message Disposition Notifications, when used in the HTTP reply context, will closely parallel a SMTP MDN. For example, the disposition field is a required element in the machine readable second part of a multipart/report for a MDN. The final-recipient-field ([5] section 3.1) value should be derived from the entity headers of the request. If the "To" field is missing, for signed messages, the value for Original-recipient may be the email address field from the signer's X.509 attribute for email addresses, if that value is available. For a MDN, an application must report the Message-ID of the request. The human readable part (the first part of the multipart/report) should include items such as the subject, date and other information when those fields are present in entity header fields following the POST request. The HTTP reply should normally omit the third optional part of the multipart/report (used to return the original message or its headers in Moberg, Drummond, [page 24] HTTP Transport for Secure EDI Jan 2003 the SMTP context). 8. Public key certificate handling 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 [11] email address and http URL/URI. The procedures for establishing a trading partnership and configuring the secure EDI messaging system might vary among trading partners and software packages. X.509 certificates are REQUIRED. It is RECOMMENDED that trading partners self-certify each other if an agreed upon certification authority is not used. This applicability statement does NOT require the use of a certification authority. The use of a certification authority is therefore OPTIONAL. Certificates may be self-signed. It is 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. 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 . 9. 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 plaintext. 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. The following certificate types MUST be supported. With URL Without URL Self Certified Certification Authority Certified Moberg, Drummond, [page 25] HTTP Transport for Secure EDI Jan 2003 The URL, which matches the source server identity, SHOULD be carried in the certificate. However, the receiver SHOULD NOT expect that the certificate would contain a matching URL. Since the certificates were exchanged with the establishing of the trading partner relationship, the server identify may be ignored. The complete certification chain MUST be included in all certificates. All certificate verifications MUST "chain to root". Additionally, the certificate hash should match the hash recomputed by the receiver. 10. Acknowledgements Carl Hage, Karen Rosenfeld, Chuck Fenton and many others have provided valuable suggestions improving this applicability statement. The authors would also like to thank the vendors who participated in the Drummond Group Inc AS2 interoperability testing. Their contributions led to great improvement in the clarity of this document. 11. References [1] N. Borenstein, N.Freed, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, December 02, 1996. N. Borenstein, N.Freed, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, December 02, 1996. N. Borenstein, N.Freed, "Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples", RFC 2049 , December 02, 1996. [2] D. Crocker, "MIME Encapsulation of EDI Objects", RFC 1767, March 2, 1995. [3] R. Fielding, J.Gettys, J. Mogul, H. Frystyk, T. Berners-Lee, "Hypertext Transfer Protocol--HTTP/1.1", RFC 2616, March 1997. [4] T. Harding, R. Drummond, C. Shih, "Peer-to-Peer MIME-based Secure Business Data Interchange", RFC 3335, September 2002. [5] R. Fajman, "An Extensible Message Format for Message Disposition Notifications", RFC 2298, March 1998. [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] B. Ramsdell, "S/MIME Version 3 Message Specification; Cryptographic Message Syntax", RFC 2633 RFC 2630, June 1999. [9] G. Vaudreuil, "The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages", RFC 1892, March 15, 1996. [10] T. Dierks,C. Allen, "The TLS Protocol Version 1.0" RFC 2246, March 1999. [11] D. Crocker, "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822, August 13, 1982. [12] E. Whitehead, M. Murata, "XML Media Types", RFC 2376, July 1998. 12. Authors' Addresses Dale Moberg dmoberg@cyclonecommerce.com Cyclone Commerce 8388 E. Hartford Drive, Suite 100 Scottsdale, AZ 85255 USA Dick Brooks dick.brooks@systrends.com Systrends, Inc 7855 South River Parkway, Suite 111 Tempe, Arizona 85284 USA Rik Drummond Rvd2@drummondgroup.com Drummond Group Inc. 4700 Bryant Irvin Court Fort Worth, TX 76107 USA Appendices A. Message Examples NOTE: All examples are provided as an illustration only, and are not considered part of the protocol specification. If an example conflicts with the protocol definitions specified above or in the other referenced RFC's, the example is wrong. A.1 Signed message requesting a signed, synchronous receipt POST /invoke/wm.EDIINT/receive HTTP/1.0 Host: 208.234.160.12:80 User-Agent: AS2 Company Server Date: Wed, 31 Jul 2002 13:34:50 GMT From: mrAS2@as2.com AS2-Version: 1.1 AS2-From: "\" as2Name \"" AS2-To: "0123456780000" Subject: G1 Message-Id: <200207310834482A70BF63@\"~~foo~~\"> Disposition-Notification-To: mrAS2@as2.com Disposition-Notification-Options: signed-receipt-protocol=optional,pkcs7-signature; signed-receipt-micalg=optional,sha1 Content-Type: multipart/signed; boundary="as2BouNdary1as2"; protocol="application/pkcs7-signature"; micalg=sha1 Content-Length: 2464 --as2BouNdary1as2 Content-Type: application/edi-x12 Content-Disposition: Attachment; filename=rfc1767.dat Moberg, Drummond, [page 26] HTTP Transport for Secure EDI Jan 2003 [ISA ...EDI transaction data...IEA...] --as2BouNdary1as2 Content-Type: application/pkcs7-signature [omitted binary pkcs7 signature data] --as2BouNdary1as2-- A.2 MDN for Message A.1 Above HTTP/1.0 200 OK Set-Cookie: ssnid=35MdRcIFhez60mO6UDq+JDMWoumBQ=666612; path=/; AS2-From: "0123456780000" AS2-To: "\" as2Name \"" AS2-Version: 1.1 Message-ID: <709700825.1028122454671.JavaMail@ediXchange> Content-Type: multipart/signed; micalg=sha1; protocol="application/pkcs7-signature"; boundary="----=_Part_57_648441049.1028122454671" Connection: Close Content-Length: 1980 ------=_Part_57_648441049.1028122454671 & Content-Type: multipart/report; Report-Type=disposition-notification; & boundary="----=_Part_56_1672293592.1028122454656" & &------=_Part_56_1672293592.1028122454656 &Content-Type: text/plain &Content-Transfer-Encoding: 7bit & &MDN for - & Message ID: <200207310834482A70BF63@\"~~foo~~\"> & From: "\" as2Name \"" & To: "0123456780000" & Received on: 2002-07-31 at 09:34:14 (EDT) & Status: processed & Comment: This is not a guarantee that the message has been completely processed or &understood by the receiving translator & &------=_Part_56_1672293592.1028122454656 & Content-Type: message/disposition-notification & Content-Transfer-Encoding: 7bit & & Reporting-UA: AS2 Server & Original-Recipient: rfc822; "0123456780000" & Final-Recipient: rfc822; "0123456780000" & Original-Message-ID: <200207310834482A70BF63@\"~~foo~~\"> & Received-content-MIC: 7v7F++fQaNB1sVLFtMRp+dF+eG4=, sha1 & Disposition: automatic-action/MDN-sent-automatically; processed & & ------=_Part_56_1672293592.1028122454656-- ------=_Part_57_648441049.1028122454671 Content-Type: application/pkcs7-signature; name=smime.p7s Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename=smime.p7s MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQ cp24hMJNbxDKHnlB9jTiQzLwSwo+/90Pc87x+Sc6EpFSUYWGAAAAAAAA ------=_Part_57_648441049.1028122454671-- Moberg, Drummond, [page 27] HTTP Transport for Secure EDI Jan 2003 Notes: 1. The lines proceeded with "&" is what the signature is calculated over. 2. 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".) 3. 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. 4. 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. However, it is RECOMMENDED that this body part be omitted or left blank. A.3 Signed, encrypted message requesting a signed, asynchronous receipt A.4 Asynchronous MDN for Message A.3 Above B. IANA Registration Form A.1 IANA registration of the signed-receipt-protocol content disposition parameter Parameter-name: signed-receipt-protocol Syntax: See section 7.3 of this document Specification: See section 7.3 of this document A.2 IANA registration of the signed-receipt-micalg content disposition parameter Parameter-name: signed-receipt-micalg Syntax: See section 7.3 of this document Specification: See section 7.3 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 7.4.3 of this document Specification: See section 7.4.3 of this document Moberg, Drummond, [page 28] HTTP Transport for Secure EDI Jan 2003