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EDIINT Working Group                                 Chuck Shih
draft-ietf-ediint-as1-08.txt                         Mats Jansson
Expires: Dec 1998                                    Rik Drummond
                                                     May 1998

                             MIME-based Secure EDI

                          draft-ietf-ediint-as1-08.txt

Status of this Memo

This document is an Internet-Draft.  Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups.  Note that other groups may also distribute
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(US West Coast).

Copyright Notice

Copyright (c) The Internet Society (1998). All rights reserveds.

Abstract

This document describes how to securely exchange EDI documents
using MIME and public key cryptography.

Feedback Instructions:

If you want to provide feedback on this draft, follow these guidelines:

  -Send feedback via e-mail to the ietf-ediint list for discussion, with
   "AS#1"” in the Subject field. To enter/follow the discussion, you
   need to subscribe at 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.







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Table of Contents

    Security Considerations                                             3
1.  Introduction                                            3

2.   Overview                                               4
   2.1  Purpose of a security guideline for MIME EDI        4
   2.2 Definitions
      2.2.1 Terms                                           4
      2.2.2 The secure transmission loop                    5
      2.2.3 Definition of receipts                          5
   2.3  Assumptions
      2.3.1 EDI process assumptions                         6
      2.3.2 Flexibility assumptions                         7

3. Referenced RFCs and their contribution                   8
   3.1 RFC 821 SMTP [7]                                     8
   3.2 RFC 822 Text Message Format [3]                      9
   3.3 RFC 1847 MIME Security Multiparts [6]                9
   3.4 RFC 1892 Multipart/report [9]                        9
   3.5 RFC 1767 EDI Content [2]                             9
   3.6 RFC 2015 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 2311 & 2312 S/MIME V2 Message Specification [8]  9

4. Structure of an EDI MIME message - Applicability         10
   4.1 Introduction                                         10
   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            11
      4.3.1 No encryption, no signature                     11
      4.3.2 No encryption, signature                        11
      4.3.3 Encryption, no signature                        11
      4.3.4 Encryption, signature                           11

5. Receipts                                                 11
   5.1 Introduction                                         11
   5.2 Requesting a signed receipt                          14
      5.2.1 Additional signed receipt considerations        15
   5.3 Message Disposition Notification Format              16
      5.3.1 Message Disposition Notification Extensions     18
      5.3.2 Disposition Mode, Type and Modifier Use         19
           5.3.2.1 Successful Processing                    19
           5.3.2.2 Unprocessed Content                      19
           5.3.2.3 Content Processing Errors                20
           5.3.2.4 Content Processing Warnings              21
   5.4 Message Disposition Notification Processing          21
      5.4.1 Large File Processing                           21
      5.4.2 Example                                         22







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6. Public key certificate handling                          24
   6.1 Near term approach                                   24
   6.2 Long term approach                                   24

7.  Acknowledgments                                         25

8.  References                                              26

9.  Authors' Addresses                                      27


Security Considerations

   This document discusses the mechanisms, requirements
   and technologies necessary to conduct secure EDI over
   Internet using either PGP/MIME or S/MIME. It further
   discusses the implementation of encryption, digital
   signature, integrity and signed-receipt for MIME objects
   transported over SMTP or HTTP.


1.  Introduction

     Previous work on Internet EDI focused on specifying MIME content
     types for EDI data ([2] RFC 1767).  This Applicability Statement
     expands on RFC 1767 to specify use of a comprehensive set of data
     security features, specifically data privacy, data
     integrity/authenticity, non-repudiation of origin and non-
     repudiation of receipt.  This draft recognizes contemporary RFCs
     and Internet drafts and is attempting to "re-invent" as little as
     possible.

     With an enhancement in the area of "receipts", as described below
     (3.1.8), secure Internet MIME based EDI can be accomplished by
     using and complying with the following RFCs:

        -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 MIME/PGP
        -RFC 2045 to 2049 MIME RFCs
        -RFC 2298 Message Disposition Notification
        -RFC 2311 S/MIME 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 Applicability Statement.

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     Note that 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  Purpose of a security guideline for MIME EDI

     The purpose of these specifications is to ensure interoperability
     between EDI user agents, invoking some or all of the commonly
     expected security features. This standard is also NOT limited to
     strict EDI use, but applies to any electronic commerce application
     where business data needs to be exchanged over the Internet in a
     secure manner.

2.2 Definitions

    2.2.1. Terms

    EDI                    Electronic Data Interchange

    EC                     Electronic Commerce

    Receipt                The functional message that is sent from a
                           receiver to a sender to acknowledge receipt
                           of an EDI/EC interchange.

    Signed Receipt         Same as above, but with a digital signature.

    Message Disposition    The 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 the
    Receipt (NRR)          original sender of an EDI/EC interchange has
                           verified the signed receipt coming back from
                           the receiver.  NRR IS NOT a functional or a
                           technical message.

    PGP/MIME               Digital envelope security based on the Pretty
                           Good Privacy (PGP) standard (Zimmerman),
                           integrated with MIME Security Multiparts [6].


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   S/MIME                   A format and protocol for adding cryptographic
                            signature and/or encryption services to
                            Internet MIME messages.



    2.2.2 The secure transmission loop

    The functional requirements document, [9] "Requirements for Inter-
    operable Internet EDI" (can be found at www.ietf.org), provides
    extensive information on EDI security and the user/business related
    processes surrounding the need for and use of EDI security.  In
    this document, it is assumed that the reader is familiar with the
    requirements document.

    This document's focus is on the formats and protocols for
    exchanging EDI content that has had security applied to it using
    the Internet's messaging transport.

    The "secure transmission loop" for EDI involves one organization
    sending a signed and encrypted EDI interchange to another
    organization, requesting a signed receipt, followed later by the
    receiving organization sending this signed receipt back to the
    sending organization.  In other words, the following transpires:

       -The organization sending EDI/EC data encrypts the data and
       provides a digital signature, using either PGP/MIME or S/MIME.
       In addition, they request a signed receipt.

       -The receiving organization decrypts the message and verifies
       the signature, resulting in verified integrity of the data and
       authenticity of the sender.

       -The receiving organization then sends a signed receipt in the
       form of a signature over the hash of a message disposition
       notification, which contains a hash of the received message.

    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 EDI
    trading partners.

    2.2.3 Definition of receipts

    The term used for both the functional activity and message for
    acknowledging receipt of an EDI/EC interchange is receipt, or

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    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 "rule" is:  If a
    receipt is requested, explicitly specifying that the receipt be
    signed, then the receipt MUST be returned with a signature.
    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, all bets are off -- 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 sender
    and content of a signed receipt.  Note that NRR is not possible
    without signatures.


2.3  Assumptions

     2.3.1 EDI process assumptions

        -Encrypted object is an EDI Interchange

        This specification assumes that a typical EDI interchange is
        the lowest level object that will be subject to security
        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 VAN-to-
        Internet routing, work may need to be done in the future to
        define ways to pull out some of the envelope information to make
        them visible, however, this specification does not go into any
        detail on that.

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        -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.

     2.3.2 Flexibility assumptions

        -Encrypted or un-encrypted 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 un-signed data

        This specification allows for EDI message exchange with or
        without digital signature of the original EDI transmission.

        -Use of receipt or not

        This specification allows for EDI message transmission with or
        without a request for receipt notification.  If a signed receipt
        notification is requested however, a signature is REQUIRED as
        part of the returned receipt, unless an error condition occurs
        in which a signed-receipt 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, as reflected in [4] "MIME Security with Pretty Good
        Privacy" (PGP), and RFC 2311/ 2312  [8] "S/MIME Message
        Specification; PKCS Security Services for MIME". Compliance with
        this specification REQUIRES the use of PGP/MIME or S/MIME
        as defined in this Applicability statement, and the [9]
        "Requirements for Inter-operable Internet EDI" draft.

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        -Hash function, message digest choices

        When 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 un-encrypted data, does NOT request a receipt.

        (2) Sender sends un-encrypted 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 un-signed receipt.

        (5) Sender sends signed data, does NOT request a signed or
            un-signed receipt.

        (6) Sender sends signed data, requests a signed or un-signed
            receipt. Receiver sends back the signed or un-signed receipt.

        (7) Sender sends encrypted and signed data, does NOT request a
            signed or un-signed receipt.

        (8) Sender sends encrypted and signed data, requests a signed or
            un-signed receipt. Receiver sends back the signed or un-
            signed 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. 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.


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     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 [10]

     This RFC defines the use of the multipart/report content type,
     something that the MDN RFC 2298 builds upon.

     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 PGP/MIME [4]

     This RFC defines the use of content types
     "multipart/encrypted", "multipart/signed", "application/pgp
     encrypted" and "application/pgp-signature" for defining MIME PGP
     content.

     3.7 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 and the "Requirements" specification.

     3.9 RFC 2311 and 2312 S/MIME Message Specifications [8]

     This specification describes how MIME shall carry PKCS7
     envelopes.

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4. 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.  The "requirements document" has several
   examples described in an Appendix for those interested.

   Also, these structures describe the initial transmission only.
   Receipts, and requests for receipts are handled in section 5.


   4.2 Structure of an EDI MIME message - PGP/MIME

      4.2.1 No encryption, no signature

      -RFC822/2045
          -RFC1767 (application/EDIxxxx)


        4.2.2 No encryption, signature

      -RFC822/2045
          -RFC1847 (multipart/signed)
              -RFC1767 (application/EDIxxxx)
              -RFC2015 (application/pgp-signature)


        4.2.3 Encryption, no signature

      -RFC822/2045
          -RFC1847 (multipart/encrypted)
              -RFC2015 (application/pgp-encrypted)
                  -"Version 1"
                  -RFC1767 (application/EDIxxxx) (encrypted)


        4.2.4 Encryption, signature

      -RFC822/2045
          -RFC1847 (multipart/encrypted)
              -RFC2015 (application/pgp-encrypted)
                  -"Version 1"
                  -RFC1767 (application/EDIxxxx) (encrypted)
                  -RFC2015 (application/pgp-signature) (encrypted)

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   4.3 Structure of an EDI MIME message - S/MIME

      4.3.1 No encryption, no signature

      -RFC822/2045
          -RFC1767 (application/EDIxxxx)


        4.3.2 No encryption, signature

      -RFC822/2045
          -RFC1847 (multipart/signed)
                  -RFC1767 (application/EDIxxxx)

                  -RFC2311 (application/pkcs7-signature)


        4.3.3 Encryption, no signature

      -RFC822/2045
          -RFC2311 (application/pkcs7-mime)
              -RFC1767 (application/EDIxxxx) (encrypted)


        4.3.4 Encryption, signature

      -RFC822/2045
          -RFC2311 (application/pkcs7-mime)
             -RFC1847 (multipart/signed) (encrypted)
                 -RFC1767 (application/EDIxxxx) (encrypted)
                 -RFC2311 (application/pkcs7-signature) (encrypted)


5. 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:



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 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
     message disposition notification.
 3). The ability to digitally sign the MIC.
 4). The ability to create a multipart/signed content with the message
     disposition notification as the first body part, and the signed
     MIC calculated on the message disposition notification as the
     second body part.
 5). 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.

     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.



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         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"

                  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 multi-part MIME content that contains the EDI Interchange
is then enveloped in either S/MIME or PGP/MIME format.

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

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         authenticated the sender of the EDI Interchange.

     4). As a non-repudiation of receipt when the signed MIC calculated
         over the MDN, is successfully decrypted by the sender with the
         receiving trading partner's public key.

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:

  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 the Disposition-notification-options string could be either

 optional, signed-receipt-protocol, <protocol symbol>;

 optional, signed-receipt-micalg, <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 signed-receipt-micalg is a list of MIC algorithm values defined in
RFC1847, an IANA registered MIC algorithm ID token.

An example of a formatted options line would be as follows:

Disposition-notification-options: optional, signed-receipt-protocol,
          pkcs7-signature;  optional, signed-receipt-micalg, 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-

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    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, 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.

     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.


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    3). When a signature is not explicitly requested, or if the
        signed receipt request parameter is not recognized by the UA,
        then all bets are off. In this situation, 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, or the multipart 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,
      or the multipart 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 or
      Content-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


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   - 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 disposi-
                           tion type was a result of an automatic
                           action, rather than an explicit instruc-
                           tion by the user for this message.

      "manual-action" -  The disposition described by the disposi-
                         tion 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".

   - 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 gener-
                   ation 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 dis-
                   position type with appropriate disposition modifiers
                   is to be used in such situations.

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    - 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, then it is RECOMMENDED that the SHA1 algorithm be used
  to calculate the MIC on the received message or message contents.

  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 the one way hash function, base64
                        encoded.

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     < 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 '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.

    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

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    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 hash over the MDN. 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.

    "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


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    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 re-assemble the fragmented
     pieces.

     It is RECOMMENDED that the size of the EDI Interchange sent via
     SMTP be configurable so that if fragmentation does occur, then
     message, "partial" can be used to send the large EDI Interchange
     in smaller pieces. RFC 2045 [1] defines the use of Content-Type:
     message/partial. Support of the message/partial content type for
     use in Internet EDI is OPTIONAL.

     The receiving UA is required to re-assemble the original message
     before sending the message disposition notification to the
     original sender of the message. A message disposition notification

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     is used to specify the disposition of the entire message that was
     sent, and should not be returned by a processing UA until the
     entire message is received, even if the received message requires
     re-assembling.

     In general, EDI content compresses well, since there is repetitive
     data in most EDI Interchanges. Instead of implementing the
     message/partial, compression of the EDI Interchange can be done
     after the signature is applied to the EDI Interchange, and before
     encryption. When no signature is applied, then compression is applied
     before the encryption. Compression is an alternative solution to
     implementing Content-Type: message/partial when sending large EDI
     Interchanges on the Internet.

     Applying compression before encryption strengthens cryptographic
     security since repetitious strings are reduced.  This sequence of
     signature, compression, then encryption, or compression then
     encryption, is consistent with the order in which PGP
     implementations handle compression.

     Note: Compression is done automatically when using PGP encryption.

     The MIME standards [1], do not define a way in which to convey
     that a message has been compressed. However, RFC 2045 [1] does
     allow the definition of additional  MIME header fields to further
     describe the content of a message.

     RFC 2068 [11], the HTTP/1.1 specification does define a Content-
     Encoding field that is primarily used to convey compression
     information:

           Content-Encoding = "Content-Encoding" ":" content-coding

     where content-coding can take on the values of "gzip" or "compress".

     The gzip compression standard is further described in RFC 1952 [12],
     and compress is the standard UNIX file compression program. Both
     gzip and compress are registered with IANA.

     Trading partners can adopt the use of the Content-Encoding header if
     they need to compress their EDI data and convey the compression
     type to their trading partners.

     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.

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     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 Edi Recipient <Edi_Recipient@edicorp.com>
      &has been received, the EDI Interchange was successfully
      &decrypted and its integrity was verified. In addition, the
      &sender of the message, Edi Sender <Edi_Sender@othercorp.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:  good-edi-internet-ua.edicorp.com  (ediua 1.0)
      &Original-Recipient:  rfc822;  Edi_Recipient@edicorp.com
      &Final-Recipient:  rfc822;  Edi_Recipient@edicorp.com
      &Original-Message-ID:  <17759920005.12345@edicorp.com>
      &Disposition: automatic-action/MDN-sent-automatically; processed
      &Received-content-MIC:   Q2hlY2sgSW50XwdyaXRIQ, sha1
      &
      &--xxxxx

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      &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

@ContentType = SignedData
@version = Version
@digestAlgorithms = DigestAlgorithmIdentifiers
@signerInfos = SignerInfo
--separator--

Notes:

-The lines preceded with "&" is what the signature is calculated
 over.

-The text preceded by "@" indicates PKCS#7 defined fields and types.

 (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".)

Note: As specified by RFC 1892 [10], 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.   Public key certificate handling

     6.1 Near term approach

     In the near term, the exchange of public keys and certification

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     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 Implementation Guide Version 2. The message formats and
     S/MIME conformance requirements for certificate exchange are
     specified in this document.

     This applicability statement does NOT require the use of a
     certification authority. 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.

7.  Acknowledgments

    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.

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8. 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]  D. Crocker, "Standard for the Format of ARPA Internet Text
     Messages", STD 11,  RFC 822,  August 13, 1982.

[4]  M. Elkins, "MIME Security With Pretty Good Privacy (PGP)",  RFC
     2015, Sept. 1996.

[5]  R. Fajman, "An Extensible Message Format for Message Disposition
     Notifications", 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]  S. Dusse, "S/MIME Version 2 Message Specification; PKCS Security
     Services for MIME", RFC 2311 RFC 2312, March 1998.

[9]  C. Shih, "Requirements for Inter-operable Internet EDI",
       Internet draft: draft-ietf-ediint-req03.txt  July 1997.

[10] G. Vaudreuil, "The Multipart/Report Content Type for the Reporting
     of Mail System Administrative Messages",  RFC 1892,  January 15,
     1996.

[11] R. Fielding, J.Gettys, J. Mogul, H. Frystyk, T. Berners-Lee, "Hypertext
     Transfer Protocol -- HTTP/1.1", RFC 2068, January 1997.

[12] L. Deutsch, "GZIP File Format Specification Version 4.3", RFC 1952,
     May 23, 1996.

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9.  Authors' Addresses

Chuck Shih
chuck.shih@gartner.com
Gartner Group.
251 River Oaks Parkway
San Jose, CA 95134-1913 USA

Mats Jansson
mjansson@agathon.com
LiNK
2317 Broadway, Suite 330
Redwood City, CA 94063 USA

Rik Drummond
drummond@onramp.com
The Drummond Group
5008 Bentwood Ct.
Ft. Worth, TX 76132 USA

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