Internet Engineering Task Force (IETF)
Request for Comments: 6362
Category: Informational
ISSN: 2070-1721
K. Meadors, Ed.
Drummond Group, Inc.
August 2011

Multiple Attachments for

Electronic Data Interchange - Internet Integration (EDIINT)


The Electronic Data Interchange - Internet Integration (EDIINT) AS1, AS2, and AS3 messages were designed specifically for the transport of EDI documents. Since multiple interchanges could be placed within a single EDI document, there was not a need for sending multiple EDI documents in a single message. As adoption of EDIINT grew, other uses developed aside from single EDI document transport. Some transactions required multiple attachments to be interpreted together and stored in a single message. This Informational RFC describes how multiple documents, including non-EDI payloads, can be attached and transmitted in a single EDIINT transport message. The attachments are stored within the MIME multipart/related structure. A minimal list of content-types to be supported as attachments is provided.

Status of This Memo

This document is not an Internet Standards Track specification; it is published for informational purposes.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at

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Table of Contents

   1. Introduction ....................................................3
      1.1. Requirements Language ......................................3
   2. Using Multiple Attachments in EDIINT ............................3
      2.1. Multipart/Related Structure ................................3
      2.2. EDIINT-Features Header .....................................4
      2.3. MIC Calculation ............................................4
      2.4. Document Processing ........................................5
      2.5. Content-Types to Support ...................................5
   3. Example Message .................................................6
   4. Security Considerations .........................................7
   5. Normative References ............................................7

1. Introduction

The primary work of the EDIINT working group (WG) was to develop a secure means of transporting EDI documents over the Internet. This was described in the three WG-developed standards for secure transport over SMTP AS1 [RFC3335], HTTP AS2 [RFC4130], and FTP AS3 [RFC4823]. For most uses of EDI, all relevant information to complete a single business transaction could be stored in a single document. As adoption of EDIINT grew, new industries and businesses began using AS2 and also needed to include multiple documents in a single message to complete a trading-partner transaction. These documents were a variety of MIME media types. This Informational RFC describes how to use the MIME multipart/related body structure within EDIINT messages to store multiple document attachments. Details of computing the message integrity check (MIC) value over this body are covered. A minimum listing of MIME media types to support within the multipart/related body is given along with information on extracting these documents.

1.1. Requirements Language

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 [RFC2119].

2. Using Multiple Attachments in EDIINT

2.1. Multipart/Related Structure

Multiple payload attachments for EDIINT messages are stored within a multipart/related MIME body [RFC2387]. The multipart/related structure allows multiple MIME attachments or message payloads to be communicated in a single structure and message.

The attached payloads can be of any MIME content-type depending on the trading-partner agreement, but Section 2.5 lists the content-types that MUST be supported. The use and format of the multipart/ related body follows the rules in RFC 2387 [RFC2387], including the required type parameter to determine the root body part. The use of the optional start parameter is RECOMMENDED.

2.2. EDIINT-Features Header

To indicate support for multiple attachments (MAs), an EDIINT application MUST use the EDIINT-Features header [RFC6017]. The EDIINT-Features header indicates that the instance application can support various features, such as certification exchange. The header is present in all messages from the instance application, not just those that feature certification exchange.

For applications implementing multiple attachments, the MA-Feature-Name MUST be used within the EDIINT-Features header as listed in this ABNF [RFC5234] syntax:

      MA-Feature-Name = "multiple-attachments"

An example of the EDIINT-Features header in a message from an application supporting MA:



2.3. MIC Calculation

MIC calculation in an EDIINT message with multiple attachments is performed in the same manner as for a single EDI payload. The only difference is calculating the message integrity check (MIC) over the whole multipart/related body rather than a single EDI payload. Section 5.2.1 of AS1 [RFC3335] and Section 4 of EDIINT COMPRESSION [RFC5402] describe the MIC calculations used for a single payload document within an EDIINT message. The approach is summarized below for the multipart/related body. Refer to stated sections above for more details.

For a compressed but unsigned message, regardless of encryption, the MIC is calculated over the uncompressed multipart/related body including any applied Content-Transfer-Encoding. The body MUST be canonicalized according to the procedure described in the underlying transport protocol (e.g., HTTP AS2 [RFC4130]) before the MIC is calculated.

For an encrypted but unsigned and uncompressed message, the MIC is calculated on the decrypted multipart/related body, including the header and all attached documents. The body MUST be canonicalized according to the procedure described in the underlying transport protocol (e.g., HTTP AS2 [RFC4130]) before the MIC is calculated.

For an unsigned and unencrypted message, the MIC is calculated over the data inside the multipart/related boundaries prior to Content-Transfer-Encoding. However, unsigned and unencrypted messages SHOULD NOT be sent due to lack of security.

If the expected MIC value differs from the calculated MIC value, all attachments MUST be considered invalid and retransmitted.

2.4. Document Processing

Upon receipt of an EDIINT message with multiple attachments, the receiving user agent MUST be able to extract the attached payloads from the message rather than only removing the multipart/related body from the message. The storing or processing of the documents as they relate to the pending transaction is implementation dependent.

2.5. Content-Types to Support

Documents of the following MIME media types MAY be found in a multipart/related body and MUST be accepted by the user agent. However, any media type can be used depending upon industry need, and other media types MAY be accepted depending upon the trading-partner agreement. Please see [MIMEREG] for the definitions of the media types listed below.


3. Example Message

Below is an example AS2 message that uses two attachments. The first attachment is an XML document, which is the root attachment, and the second attachment is a PDF document. The content of both the XML and PDF documents, as well as the applied digital signature, has been omitted for size consideration. This example is provided as an illustration only and is not considered part of the specification. If the example conflicts with the definitions specified above or in the other referenced RFCs, the example is considered invalid.

      POST /as2 HTTP/1.1
      Connection: Close, TE
      Message-ID: <1109712943488@>
      Subject: Multiple Attachment Example
      Date: Tue, 01 Mar 2005 21:37:03 GMT
      AS2-To: TradingPartner
      AS2-From: User
      AS2-Version: 1.2
      EDIINT-Features: multiple-attachments
      Content-type: multipart/signed;
         protocol="application/pkcs7-signature"; micalg=sha-1;
      Content-length: 207440
      Content-type: multipart/related; boundary="INNER-BOUNDARY";
         start="<root.attachment>"; type="application/xml"
      Content-type: application/xml
      Content-ID: <root.attachment>
      Content-type: application/pdf
      Content-ID: <2nd.attachment>
      Content-type: application/pkcs7-signature

4. Security Considerations

Multiple attachments have security concerns that are very similar to those described in the three EDIINT transport standards. These include the importance of using strong cryptography and the necessity of using valid certificates and chaining to a trusted certification authority (CA). Please refer to these standards -- SMTP AS1 [RFC3335], HTTP AS2 [RFC4130], and FTP AS3 [RFC4823] -- for details of their security considerations.

The only additional security consideration is that if the MIC calculation by the user agent differs from the expected MIC calculation, all the attached documents MUST be considered invalid. Because the MIC calculation is over the multipart/related body, the MIC validates the content integrity of all the documents.

5. Normative References

   [MIMEREG]  "MIME Media Types", <>.
   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
   [RFC2387]  Levinson, E., "The MIME Multipart/Related Content-type",
              RFC 2387, August 1998.
   [RFC3335]  Harding, T., Drummond, R., and C. Shih, "MIME-based Secure
              Peer-to-Peer Business Data Interchange over the Internet",
              RFC 3335, September 2002.
   [RFC4130]  Moberg, D. and R. Drummond, "MIME-Based Secure Peer-to-
              Peer Business Data Interchange Using HTTP, Applicability
              Statement 2 (AS2)", RFC 4130, July 2005.
   [RFC4823]  Harding, T. and R. Scott, "FTP Transport for Secure Peer-
              to-Peer Business Data Interchange over the Internet",
              RFC 4823, April 2007.
   [RFC5234]  Crocker, D., Ed., and P. Overell, "Augmented BNF for
              Syntax Specifications: ABNF", STD 68, RFC 5234,
              January 2008.
   [RFC5402]  Harding, T., Ed., "Compressed Data within an Internet
              Electronic Data Interchange (EDI) Message", RFC 5402,
              February 2010.
   [RFC6017]  Meadors, K., Ed., "Electronic Data Interchange - Internet
              Integration (EDIINT) Features Header Field", RFC 6017,
              September 2010.

Author's Address

   Kyle Meadors (editor)
   Drummond Group, Inc.
   Nashville, Tennessee  37221
   Phone: +1 (817) 709-1627