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INTERNET DRAFT                                        Mats Jansson, LiNK
draft-ietf-ediint-as1-02.txt                           Chuck Shih, Actra
                                                Nancy Turaj, Mitre Corp.
                                            Rik Drummond, Drummond Group

19 November, 1996

                        MIME-based Secure EDI


Status of this Memo

     This document is an Internet-Draft.  Internet-Drafts are working
     documents of the Internet Engineering Task Force (IETF), its areas,
     and its working groups.  Note that other groups may also distribute
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     To learn the current status of any Internet-Draft, please check the
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     (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East
     Coast), or ftp.isi.edu (US West Coast).

Abstract

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


Feedback Instructions:

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

  -Send feedback via e-mail to mjansson@agathon.com, with "AS#1" in the
  Subject field.

  -Be specific as to what section you are referring to, preferably
  quoting the portion that needs modification, after which you state
  your comments.

  -If you are recommending some text to be replaced with your suggested
  text, again, quote the section to be replaced, and be clear on the
  section in question.

  -If you are questioning fundamental methods, make it clear to us and
  we will bring the issue to the ediint list for discussion.  To follow
  the discussion, you need to subscribe at ietf-ediint@imc.org.


Table of Contents

1.  Introduction

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

3. Structure of an EDI MIME message
   3.1  Referenced RFCs and their contribution
      3.1.1 RFC 821 SMTP [7]
      3.1.2 RFC 822 Text Message Format [3]
      3.1.3 RFC 1521 MIME [1]
      3.1.4 RFC 1847 MIME Security Multiparts [6]
      3.1.5 RFC 1892 Multipart/report [9]
      3.1.6 RFC 1767 EDI Content [2]
      3.1.7 RFC 2015 PGP/MIME [4]
      3.1.8 Internet draft (fajman): Message Disposition Notification
            [5]
      3.1.9 RSA Specifications - S/MIME (RSA Security, Inc.) [8]
   3.2  Vocabulary
   3.3  Structure of an EDI MIME message - No encryption/No signature
   3.4  Structure of an EDI MIME message - S/MIME
      3.4.1 S/MIME Overview
      3.4.2 Example: S/MIME - Signature Only
      3.4.3 Example: S/MIME - Encryption Only
      3.4.4 Example: S/MIME - Signature and Encryption
   3.5 Structure of an EDI MIME message - PGP/MIME
      3.5.1.PGP/MIME Overview
      3.5.2 Example: PGP/MIME - Signature Only
      3.5.3 Example: PGP/MIME - Encryption Only
      3.5.4 Example: PGP/MIME - Signature and Encryption

4. Receipts
   4.1 Introduction
   4.2 Requesting a signed receipt
   4.3 Message Disposition Notification Format
   4.4 Message Disposition Notification Processing
      4.4.1 Large File Processing
      4.4.2 Example

5.   Public key certificate handling
   5.1 Near term approach
   5.2 Long term approach

6.  Authors' Addresses

7. References



1.  Introduction

     The authors would like to extend special thanks to Carl Hage for
     providing the team with valuable, and very thorough feedback.
     Without participants like Carl, these efforts become hard to
     complete in a way useful to the users of the technology.

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

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

        -RFC 821 SMTP
        -RFC 822 Text Message Formats
        -RFC 1521 MIME
        -RFC 1767 EDI Content Type
        -RFC 1847 Security Multiparts for MIME
        -RFC 1892 Multipart/Report
        -Internet draft: Message Disposition Notification (fajman)
        -RFC 2015 MIME/PGP (elkins)
        -Internet draft: S/MIME Specification (dusse)

     Our intent here is to define clearly and precisely how these
     are pieced together and what is required by user agents to be
     compliant with this Applicability Statement.


2.   Overview

2.1  Purpose of a security guideline for MIME EDI

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


2.2 Definitions

    2.2.1. Terms

    EDI                    Electronic Data Interchange

    EC                     Electronic Commerce

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

    Signed Receipt         Same as above, but with a digital signature

    Message Disposition    The way by which a receipt or a signed
    Notification (MDN)     receipt is accomplished within Internet
                           Messaging.

    Non-repudiation of     NRR is a "legal event" that occurs when the
    Receipt (NRR)          original sender of an EDI/EC interchange has
                           verified the signed receipt coming back from
                           the receiver.  NRR IS NOT a functional or a
                           technical message.

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

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


    2.2.2 The secure transmission loop

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

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

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

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

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

       -The receiving organization then sends a "signed receipt" in the
       form of a signature over the hash from the previous step.

    The above describes functionality which if implemented, would
    satisfy all security requirements. This specification, however,
    leaves full flexibility for users to decide the degree to which they
    want to deploy those features with their EDI trading partners.


    2.2.3 Definition of receipts

    The term used for both the functional activity and message for
    acknowledging receipt of an EDI/EC interchange is "receipt", or
    "signed receipt".  The first term is used if the acknowledgment is
    for an interchange that was not signed, thereby resulting in a
    receipt which is also not signed.  The second term is used if the
    acknowledgment is for an interchange which was signed, resulting in
    a receipt which is also signed.  The rule is:  If a receipt is
    requested, it will be signed only if the original interchange was
    signed.  A term often used in combination with receipts is "Non-
    repudiation of Receipt (NRR).  NRR refers to a legal event which
    occurs only when the original sender of an interchange has verified
    the sender and content of a "signed receipt".  Note that NRR is not
    possible without signatures.


2.3  Assumptions

     2.3.1 EDI process assumptions

        -Encrypted object is an EDI Interchange

        This specification assumes that a typical EDI interchange is the
        lowest level object that will be subject to security features.
        In ANSI X12, this means anything between, and including
        segments ISA and IEA.  In EDIFACT, this means anything between,
        and including, segments UNA/UNB and UNZ.  In other words, the
        EDI interchanges including envelope segments remain intact and
        unreadable during secure transport.

        -EDI envelope headers are encrypted

        Congruent with the above statement, EDI envelope headers are NOT
        visible in the MIME package.  In order to optimize VAN-to-
        Internet routing, work may need to be done in the future to
        define ways to pull out some of the envelope information to make
        them visible, however, this specification does not go into any
        detail on that.

        -X12.58 and UN/EDIFACT security considerations

        The most common EDI standards, ANSI X12 and EDIFACT, have
        defined internal provisions for security.  X12.58 is the
        security mechanism for ANSI X12 and AUTACK provides security for
        EDIFACT.  This specification DOES NOT dictate use or non-use of
        these security standards.  They are both fully compatible,
        though possibly redundant, with this specification.


     2.3.2 Flexibility assumptions

        -Encrypted or un-encrypted data

        This specification allows for EDI message exchange where the EDI
        data is either un-protected or protected by means of encryption.

        -Signed or un-signed data

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

        -Use of receipt or not (signature required for "Signed Receipt")

        This specification allows for EDI message transmission with or
        without a request for receipt notification.  If receipt
        notification is requested, however, a signature is required as
        part of both the original EDI transmission and the returned
        receipt.

        -Formatting choices

        This specification defines use of two methods for formatting EDI
        contents that have security applied to it:

           -PGP/MIME
           -S/MIME

        This specification relies on the guidelines set forth in the
        Internet draft on PGP/MIME, as reflected in [4] MIME Security
        with Pretty Good Privacy (PGP), and [8] S/MIME Specification
        from RSA Security, Inc.  Compliance with this specification
        dictates that AT LEAST one of these methods is supported.

        -Hash function, message digest choices

        When signature is used, unless specified otherwise by the chosen
        method (PGP/MIME or S/MIME), the MD5 checksum hash function is
        recommended.


        In summary, the following eight permutations are possible, in
        any given trading relationship:

        (1) Sender sends un-encrypted data, does NOT request a receipt.

        (2) Sender sends unencrypted data, requests a receipt. Receiver
            sends back a receipt.

        (3) Sender sends encrypted data, does NOT request a receipt.

        (4) Sender sends encrypted data, requests a receipt. Receiver
            sends back a receipt.

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

        (6) Sender sends signed data, requests a signed receipt.
            Receiver sends back a signed receipt.

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

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

        NOTE: Users can choose any of the eight possibilities, but only
        example (8) offers the whole suite of security features
        described in the "Secure transmission loop" above.

        NOTE: A request for receipt that is signed, MUST result in a
        signed receipt.  A request for receipt without signature MUST
        result in an un-signed receipt.


3.   Structure of an EDI MIME message

     The following sub chapters describe the structure of EDI MIME
     messages, making use of security features in different ways.
     Please note that if a signed receipt is to be returned, the
     original EDI transmission also had to have been signed.

     The structures shown below represent the use of specifications
     outlined in the following RFCs and Internet-drafts, and before
     moving into the structures themselves, there is a brief review of
     what each document contributes.

     NOTE: The examples below are just that - examples.  Do not code
     according to them.  Refer to the RFCs that specify the correct
     grammar in each case.


3.1  Referenced RFCs and their contribution

     3.1.1 RFC 821 SMTP [7]

     This is the core mail transfer standard that all MTAs need to
     adhere to.


     3.1.2 RFC 822 Text Message Format [3]

     Defines message header fields and the parts making up a message.


     3.1.3 RFC 1521 MIME [1]

     This is  the basic MIME standard, upon which all MIME related RFCs
     build, including this one.  Key contributions include definition of
     "content type" and sub-type "multipart", in addition to encoding
     guidelines,  which establish 7-bit US-ASCII as the lowest common
     denominator used.


     3.1.4 RFC 1847 MIME Security Multiparts [6]

     This document defines security multiparts for MIME:
     multipart/encrypted and multipart/signed.


\     3.1.5 RFC 1892 Multipart/report [10]

     This RFC defines the use of Multipart/report content type,
     something that the MDN draft (fajman) relies on for the receipt
     functionality.


     3.1.6 RFC 1767 EDI Content [2]

     This RFC defines the use of content type "application" for ANSI
     X12 (application/EDI-X12), EDIFACT (application/EDIFACT) and
     mutually defined EDI (application/EDI-Consent).


     3.1.7 RFC 2015 PGP/MIME [4]

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


     3.1.8 Internet draft (fajman): Message Disposition Notification [5]

     This Internet draft defines how a message disposition notification
     (MDN) is requested, and the structure of the MDN.

     NOTE: This is the only specification we were not able to take
     "as is". Extension field-names beginning with "X-" will not be
     defined as a standard field. MDN field names not beginning with "X-
     " need to be registered with the Internet Assigned Numbers
     Authority (IANA) and described in an RFC. The X-Received-MIC field
     described in this document will be registered with IANA.


     3.1.9 Internet draft (dusse): S/MIME Message Specification [8]

     This specification describes how MIME shall carry PKCS7
     signature and envelope information.


3.2  Vocabulary

     <recipient email>         The email address of the receiving
                               organization's EDI processing system.

     <sender email>            The email address of the sending organi-
                               zation's EDI processing system.

     <date>                    Transmission date

     <EDI standard>            "EDIFACT" or "EDI-X12" or "EDI-consent"

     <encoding>                "Quoted-printable" or "Base64"

     <EDI Object>              ANSI X12 or EDIFACT EDI Interchange, or
                               mutually agreed electronic commerce file

     <char set>                "us-ascii" or "iso-8859-1" (note that if
                               iso-8859-1 is used, in most cases
                               encoding will be required "Quoted
                               printable" or "Base 64"

     <hash symbol>             "md5" or "sha1"

     <pgp control information> -Key ID of recipient's public key
                               -Session key (symmetric)
                               -Timestamp
                               -Key ID of sender's public key
                               -Leading two octets of message digest
                               -Message digest
                               -Filename
                               -Timestamp

     <PKCS#7 control information - enveloped>
                               -contentType = EnvelopedData
                               -version = Version
                               -recipientInfos = RecipientInfos

                               -contentType = Data
                               -contentEncryptionAlgorithm =
                                ContentEncryptionAlgorithmIdentifier

                               -encryptedContent =

     <PKCS#7 control information - signed>
                               -ContentType = SignedData
                               -version = Version
                               -digestAlgorithms =
                                DigestAlgorithmIdentifiers
                               -contentType = Data
                               -content =

     <PKCS#7 signature information>
                               -signerInfos = SignerInfo

     NOTE: The examples below are just that - examples. They are
     provided for illustration purposes only. Refer to the RFCs or
     drafts under "7. References" for the actual grammar and protocol
     definitions.


3.3  Structure of an EDI MIME message - No encryption/No signature

To:             <recipient email>
Subject:
From:           <sender email>
Date:           <date>
Mime-Version:   1.0
Content-Type: Application/<EDI standard>
Content-Transfer-Encoding: <encoding>

<EDI object>


3.4  Structure of an EDI MIME message - S/MIME

      3.4.1 S/MIME Overview

      S/MIME or the Secure/Multipurpose Internet Mail Extensions,
      specify formats and procedures when the cryptographic security
      services of authentication, message integrity, non-repudiation of
      origin, and confidentiality are applied to Internet MIME messages.

      S/MIME is specified in draft draft-dusse-mime-msg-spec-00.txt, and
      an S/MIME implementation guide is available from RSA Data
      Securities, Inc.

      This applicability statement sets forth the implementation
      requirements and recommendations needed to use S/MIME when sending
      EDI on the Internet. These implementation requirements and
      recommendations are intended to ensure a base level of inter-
      operability among S/MIME EDI implementations.

      NOTE: The S/MIME Implementation Guide, Version 2 specifies a
      restricted profile for use for export purposes and an unrestricted
      profile for use domestically.  These profiles specify the
      cryptographic algorithms and key lengths that a conformant S/MIME
      implementation must support. It is recommended that for Internet
      EDI, these profiles be adhered to. However, cryptographic
      algorithms, and key lengths are parameters that need to be set by
      the trading partnership, and can vary from what is specified by
      the S/MIME standards.

      Content Types:

      signedAndEnvelopedData content type should not be
      used when sending EDI on the Internet. Objections have been raised
      concerning the fact that the issuerAndSerialNumber for each signer
      of a signedAndEnvelopedData content is left in the clear. This
      information could be used to derive the identity of the signer
      of the message. The use of signedAndEnvelopedData also precludes
      the ability to sign information that is in addition to, but
      separate from the primary signed contents. The use of the S/MIME
      "authenticated attributes" is not required for Internet EDI, since
      it is generally sufficient to sign the EDI MIME content.

      The S/MIME Implementation Guide, Version 2 requires a compliant
      S/MIME agent to support the nesting of a signed message format
      within an enveloped message, for both incoming and outgoing
      messages. This EDI AS#1 specification also requires the support of
      a nested signed message within an enveloped message. Therefore,
      when using S/MIME for the purpose of sending EDI on the Internet,
      a two step process will be used: the user agent first creates an
      application/x-pkcs7-mime signed message, and uses this message as
      input to the creation of an application/x-pkcs7-mime enveloped
      message.

      The receiver of an incoming enveloped message that is decrypted
      and found to contain a signed application/x-pkcs-7-mime type,
      should process the signed contents and present the signature
      status and corresponding "data" content to message disposition
      notification processing -- if a request for a message disposition
      notification has been made -- otherwise the "data" content is
      passed to a general MIME processor.

      The "data" content type is used as the content within the
      signedData and the envelopedData content types, to indicate the
      MIME message content which has had security services applied to
      it. For the purpose of Internet EDI, this "data" content type will
      contain RFC 1767 specified MIME EDI content, or a MIME multipart
      content that has a RFC 1767 MIME EDI content as part of the
      multipart content.

      Signed Message Type:

      The S/MIME specification requires support of the signedData
      content format, and recommends support of the multipart/signed
      format. For use in Internet EDI, support is required for the
      signedData content format if message authentication, integrity,
      and non-repudiation of origin are required. The great value for
      support of the multipart/signed format is the ability of non-
      S/MIME-enabled agents to process the content of the body that was
      signed.

      The multipart/signed format is recommended when a signed message
      is being sent to a set of recipients, not all of which are known
      to have S/MIME enabled agents. Since trading partners using S/MIME
      to transact EDI on the Internet will by definition have S/MIME-
      enabled agents, the multipart/signed loses much of its utility.
      Support of the multipart/signed format for use in Internet EDI is
      therefore optional.


      3.4.2 Example: S/MIME - Signature Only

To:             <recipient email>
Subject:
From:          <sender email>
Date:           <date>
Mime-Version:   1.0
Content-Type: application/x-pkcs7-mime
Content-Transfer-Encoding: base64

<PKCS#7 control information - signed>

      &Mime-Version:   1.0
      &Content-Type: Application/<EDI standard>;
      &Content-Transfer-Encoding: <encoding>
      &
      &<EDI object>

<PKCS#7 signature information>


Notes:

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

- <PKCS#7 control information - signed> consists of (refer to:
PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.):

    ContentType = SignedData
    version = Version
    digestAlgorithms = DigestAlgorithmIdentifiers
    contentType = Data
    content =

    NOTE: that except for ContentType and Content, the actual object
    identifiers or values for the fields are not specified. (See PKCS#9
    and the S/MIME Implementation Guide, Version 2 from RSA Labs, Inc.,
    for these object identifiers.)

- <PKCS#7 signature information> consists of (refer to:
PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.):

    signerInfos = SignerInfo

    NOTE: The signerInfo contains the digestAlgorithm, the
    digestEncryptionAlgorithm, and the encryptedDigest or the digital
    signature. The issuerAndSerialNumber field defined within the
    signerInfos identifies a signing trading partner's public-key
    certificate. Since Internet EDI allows self-certification, this
    field can contain the distinguished name of the sending trading
    partner for the issuer distinguished name.


      3.4.3 Example: S/MIME - Encryption Only

To:             <recipient email>
Subject:
From:         <sender email>
Date:          <date>
Mime-Version: 1.0
Content-Type: application/x-pkcs7-mime
Content-Transfer-Encoding: base64

<PKCS#7 control information - enveloped>

      &Mime-Version:   1.0
      &Content-Type: Application/<EDI standard>;
      &Content-Transfer-Encoding: <encoding>
      &
      &<EDI object>


Notes:

-The text preceded by "&" indicates that it is really encrypted,
but presented as text for clarity

- <PKCS#7 control information - enveloped> consists of (See
PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.):

    contentType = EnvelopedData
    version = Version
    recipientInfos = RecipientInfos

    contentType = Data
    contentEncryptionAlgorithm = ContentEncryptionAlgorithmIdentifier

    encryptedContent =

    NOTE: Except for contentType, the actual object identifiers or
    values for the fields are not specified. (See PKCS#9 and the S/MIME
    Implementation Guide, Version 2 from RSA Labs, Inc., for these
    objects.)

    NOTE: The recipientInfos contains the symmetric encryption key
    encrypted with the receiver's public key. The issuerAndSerialNumber
    field defined within the recipientInfos identifies a receiving
    trading partner's public-key certificate. Since Internet EDI allows
    self-certification, this field can contain the distinguished name of
    the receiving trading partner for the issuer distinguished name.

    NOTE: In general there will be one recipientInfos specified, but in
    the case of RFQs there may be n recipientInfos specified.


      3.4.4 Example: S/MIME - Signature and Encryption

The required support for EDI Internet is to first create an
application/x-pkcs7-mime signedData message, and then to create an
application/x-pkcs7-mime envelopedData message with the application/x-
pkcs7-mime signedData message as input to the application/x-pkcs7-mime
envelopedData message.

To:             <recipient email>
Subject:
From:         <sender email>
Date:          <date>
Mime-Version: 1.0
Content-Type: application/x-pkcs7-mime
Content-Transfer-Encoding: base64

<PKCS#7 control information - enveloped>

         *Mime-Version:  1.0
         *Content-Type: application/x-pkcs7-mime

         *<PKCS#7 control information - signed>

              *&MIME-Version:   1.0
              *&Content-Type: Application/<EDI standard>;
              *&Content-Transfer-Encoding: <encoding>

              *&<EDI object>

         *<PKCS#7 signature information>


Notes:

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

- The text preceded by "*" indicates that it is really encrypted, but
presented as text for clarity

- <PKCS#7 control information - enveloped> consists of (See
PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.):

    contentType = EnvelopedData
    version = Version
    recipientInfos = RecipientInfos

    contentType = Data
    contentEncryptionAlgorithm = ContentEncryptionAlgorithmIdentifier

    encryptedContent =

    NOTE: Except for contentType, the actual object identifiers or
    values for the fields are not specified. (See PKCS#9 and the S/MIME
    Implementation Guide, Version 2 from RSA Labs, Inc., for these
    objects.)

    NOTE: The recipientInfos contains the symmetric encryption key
    encrypted with the receiver's public key. The issuerAndSerialNumber
    field defined within the recipientInfos identifies a receiving
    trading partner's public-key certificate. Since Internet EDI allows
    self-certification, this field can contain the distinguished name of
    the receiving trading partner for the issuer distinguished name.

    NOTE: In general there will be one recipientInfos specified, but in
    the case of RFQs there may be n recipientInfos specified.

- <PKCS#7 signature information> consists of (refer to:
PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.):

    signerInfos = SignerInfo

    NOTE: The signerInfo contains the digestAlgorithm, the
    digestEncryptionAlgorithm, and the encryptedDigest or the digital
    signature. The issuerAndSerialNumber field defined within the
    signerInfos identifies a signing trading partner's public-key
    certificate. Since Internet EDI allows self-certification, this
    field can contain the distinguished name of the sending trading
    partner for the issuer distinguished name.


   3.5 Structure of an EDI MIME message - PGP/MIME

      3.5.1 Overview

      PGP provides two functional services, signature and encryption,
      but in reality performs 5 functions in order to do it effectively.

      1) Digital signature (MD5, RSA)
      2) Compression (ZIP)
      3) Message Encryption (IDEA)
      4) ASCII Armor
      5) Message segmentation

      When sending a message, the services are performed in that order.

      With the exception of item 5), these services are optional,
      meaning a user can choose whether to use signature, encryption,
      compression and ASCII armor, but commonly, 2) and 4) are always
      used, while 1) and 3) are used in three ways:

      1) Signature only, in which case ASCII armor can be applied only
         to the signature block to keep the message legible.

      2) Encryption only

      3) Both signature and encryption

      Applicability of PGP/MIME and RFC 2015, for use in internet EDI
      dictates the following:

      - When both encryption and signature feature is used, the EDI
      data is first signed, then encrypted in a two-step process, as
      described in the example.

      -Compression and ASCII Armor is optional and could be user
      configurable.

      The following examples describe use of PGP/MIME without
      compression and ASCII armor, since those services are managed by
      PGP, and are optional per this draft
.

      3.5.2 Example: PGP/MIME - Signature Only

To:             <recipient email>
Subject:
From:           <sender email>
Date:           <date>
Mime-Version:   1.0
Content-Type: multipart/signed; boundary="separator";
    micalg=pgp-<hash symbol>; protocol="application/pgp-signature"

--separator
    &Content-Type: Application/<EDI standard>
    &Content-Transfer-Encoding: <encoding>
    &
    &<EDI object>

--separator
    Content-Type: application/pgp-signature

    -----BEGIN PGP MESSAGE-----
    Version 2.6.2

    fgfjhHjhJhgljhgJGHGJHGJHJHJhghjhJHJuytIYTiutTYT34553//YRytdhfFFQere
    /876JHJHGIUIUgsdIUYgYTRdgggguytUTIUlbXssfdsfdREWrewREWREEWE88POF/DF
    frtFFKFG+GFff=
    =ndaj
    -----END PGP MESSAGE-----

--separator--

Notes:

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


      3.5.3 Example: PGP/MIME - Encryption Only

To:             <recipient email>
Subject:
From:           <sender email>
Date:           <date>
Mime-Version:   1.0
Content-Type: multipart/encrypted; boundary="separator";
    protocol="application/pgp-encrypted"

--separator
    Content-Type: application/pgp-encrypted

    Version: 1

--separator
    Content-Type: application/octet-stream

    -----BEGIN PGP MESSAGE-----
    Version 2.6.2

    &<pgp control information>
    &Content-Type: Application/<EDI standard>;
    &Content-Transfer-Encoding: <encoding>
    &
    &<EDI object>
    -----END PGP MESSAGE-----

--separator--

Notes:

-The text preceded by "&" indicates that it is really encrypted, but
presented as text for clarity

-"pgp control information" contains the following, but refer to PGP
specifications or tool kits for details:

    -Key ID of recipient's public key
    -Session key (symmetric)
    -Timestamp
    -Key ID of sender's public key
    -Leading two octets of message digest
    -Message digest
    -Filename
    -Timestamp


      3.5.4 Example: PGP/MIME - Signature and Encryption

The sequence here is that the EDI data is first signed as a
multipart/signature body, and then the data plus the signature is
encrypted to form the final multipart/encrypted body. Here goes:

To:             <recipient email>
Subject:
From:           <sender email>
Date:           <date>
Mime-Version:   1.0
Content-Type: multipart/encrypted; boundary="separator";
    protocol="application/pgp-encrypted"

--separator
    Content-Type: application/pgp-encrypted

    Version: 1

--separator
    Content-Type: application/octet-stream

    -----BEGIN PGP MESSAGE-----
    Version 2.6.2

*    <pgp control information>
*    Content-Type: multipart/signed; boundary="signed separator";
*        micalg=pgp-<hash symbol>; protocol="application/pgp-signature"
*
*    --signed separator
*        &Content-Type: Application/<EDI standard>
*        &Content-Transfer-Encoding: <encoding>
*        &
*        &<EDI object>
*
*    --signed separator
*        Content-Type: application/pgp-signature
*
*        -----BEGIN PGP MESSAGE-----
*        Version 2.6.2
*
*        fgfjhHjhJhgljhgJGHGJHGJHJHJhghjhJHJuytIYTiutTYT34553//YRytd
*        /GIUIUgsIUYgYTRdgggguytUTIUlbXssfdsfdREWrewREWREEWE88POF/DF
*        frtFFKFG+GFff=
*        =ndaj
*        -----END PGP MESSAGE-----
*
*    --signed separator--
     -----END PGP MESSAGE-----

--separator--

Notes:

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

- The text preceded by "*" indicates that it is really encrypted,
but presented as text for clarity

- "pgp control information" contains the following, but refer to
PGP specifications or tool kits for details:

    -Key ID of recipient's public key
    -Session key (symmetric)
    -Timestamp
    -Key ID of sender's public key
    -Leading two octets of message digest
    -Message digest
    -Filename
    -Timestamp

-RFC 2015 allows another way to handle the above in a combined
fashion,  However, for the purpose of EDI we require the above method,
which is based on MIME Security Multiparts [4] RFC 1847. This method
performs signature and encryption in a two-step process, first signing
the data, then encrypting it.  This is also consistent with PGP's
recommendations.


4. Receipts

4.1   Introduction

In order to provide a non-repudiation of receipt (NRR) or signed
receipt, a message disposition notification (MDN) as specified by draft-
ietf-receipt-mdn-01 is to be implemented by a receiving trading
partner's UA (User Agent). The message disposition notification
is then digitally signed and returned to the sending trading partner
as part of a multipart/signed content.

The required support for signed receipts when doing EDI Internet is as follows:

    1). Create a multipart/report; report-type=disposition-notification.
    2). Calculate the MIC on the message disposition notification.
    3). Digitally sign the MIC.
    4). Create a multipart/signed content with the message disposition
        notification as the first body part, and the signed MIC
        calculated on the message disposition notification as the
        second body part.
    5). Return the signed receipt to the sending trading partner.


The  MDN is used to notify a sending trading partner that sent a signed,
or signed and encrypted EDI Interchange that:

     1). The receiving trading partner acknowledges receipt of
         the sent EDI Interchange.

     2). The receiving trading partner has authenticated the sender of
         the EDI Interchange.

     3). The receiving trading partner has verified the integrity of the
         received EDI Interchange.

Regardless of whether the EDI Interchange was sent in S/MIME or PGP/MIME
format, the receiving trading partner's UA must provide the following
basic processing:

     1). If the sent EDI Interchange is encrypted, then the encrypted
         symmetric key and initialization vector (if applicable) is
         decrypted using the receiver's private key.

     2). The decrypted symmetric encryption key is then used to decrypt
         the EDI Interchange.

     3). The receiving trading partner authenticates signatures in a
         message using the sender's public key. The authentication
         algorithm performs the following:

         a). The message integrity check (MIC or Message Digest)
             contained within the signature is decrypted using the
             sender's public key.

         b). A MIC on the signed contents (the MIME header and encoded
             EDI object, as per RFC1767) in the message received is
             calculated using the same one-way hash function that the
             sending trading partner used.

         c). The MIC extracted from the signature is compared with the
             MIC calculated using the same one-way hash function that
             the sending trading partner used.

     4). The receiving trading partner formats the MDN and sets the
         calculated MIC into the MDN extension field.

     5). The receiving trading partner creates a multipart/signed MIME
         message according to RFC 1847.

     6). The MDN is the first part of the multipart/signed message, and
         the digital signature is created over this MDN, including its
         MIME headers.

     7). The second part of the multipart/signed message contains the
         digital signature. The "protocol" option specified in the
         multipart/signed is as follows:

                  S/MIME: protocol = "application/pkcs-7-mime"

                  PGP/MIME: protocol = "application/pgp-signature"


The EDI Interchange and the RFC 1767 MIME EDI content header, can
actually be part of a multi-part MIME content-type.  When the EDI
Interchange is part of a multi-part MIME content-type, the MIC is
calculated across the entire multi-part content, including the  MIME
headers. The multi-part MIME content that contains the EDI Interchange
is then enveloped in either PKCS #7 or PGP format.

The signed MDN, when received by the sender of the EDI Interchange can then be used by the sender:

     1). As an acknowledgment that the EDI Interchange sent, was
         delivered and acknowledged by the receiving trading partner.
         The receiver does this by returning the original message
         id of the sent message in the signed MDN.

     2). As an acknowledgment that the integrity of the EDI Interchange
         was verified by the receiving trading partner. The receiver
         does this by returning the calculated MIC of the received EDI
         Interchange (and 1767 MIME headers) in the X-Received-MIC
         field of the signed MDN.

     3). As an acknowledgment that the receiving trading partner has
         authenticated the sender of the EDI Interchange.

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

4.2 Requesting a signed receipt

Message Disposition Notifications are requested as per the draft-ietf-
receipt-mdn-01.txt. A request that the receiving user agent issue a
message disposition notification is made by placing the following header
into the message to be sent:

     mdn-request-header = "Disposition-notification-to"   ":"   address

The address field is specified as an RFC 822 user@domain address, and is
the return address for the message disposition notification.

A note to implementors: this RFC does not preclude the sending of a
signed receipt whenever EDI content is received by a trading partner.
The sending of a signed receipt can be made a configurable parameter,
and a signed receipt may be returned even though the original message
does not contain a receipt request.

4.3 Message Disposition Notification Format

The format of a message disposition notification is as specified in draft-ietf-receipt-mdn-01.txt. For use in EDI over the Internet the following format will be used:

   - content-type - per  RFC1892 and the ietf-receipt-mdn specification

   - reporting-ua-field - per ietf-receipt-mdn specification

   - mdn-gateway-field - per ietf-receipt-mdn specification

   - original-recipient-field - per ietf-receipt-mdn specification

   - final-recipient-field - per ietf-receipt-mdn specification

   - original-message-id-field - per ietf-receipt-mdn specification

   - disposition-field - for EDI use:

       * autoprocessed - when the received content(s) are
         successfully processed

       * decryption_failed - when the receiver could not decrypt the
         contents

       * authentication_failed - when the receiver could not
         authenticate the sender

       * integrity_check_failed - when the receiver could not verify
         content integrity

   - extension field - the following extension field will be added in
     order to support signed-receipts for RFC 1767 specified content
     types and multi-part specified content types which includes RFC
     1767 content types. The extension field is sent only when the
     received contents are successfully processed.

   - extension field = "X-"  "Received-MIC"  ":"  MIC

MIC or message integrity check, is defined as the result of a one-way
hash function applied to the received EDI Interchange and RFC 1767 MIME
content type information, or the multi-part MIME content containing
RFC 1767 MIME EDI content information. The MIC is also referred to as a
message digest when using the MD5 one-way hash function.


4.4 Message Disposition Notification Processing

     4.4.1  Large File Processing

     Large EDI Interchanges sent via SMTP can be automatically
     fragmented by some message transfer agents. A subtype of message,
     "partial", is defined in RFC 1521 to allow large objects to be
     delivered as separate pieces of mail and to be automatically
     reassembled by the receiving user agent. Using message, "partial",
     can help alleviate fragmentation of large messages by different
     message transfer agents, but does not completely eliminate the
     problem. It is still possible that a piece of a partial message,
     upon re-assembly, may prove to contain a partial message as well.
     This is allowed by the Internet standards, and it is
     the responsibility of the user agent to re-assemble the fragmented
     pieces.

     It is recommended that the size of the EDI Interchange sent via
     SMTP be configurable so that if fragmentation does occur, then
     message, "partial" can be used to send the large EDI Interchange
     in smaller pieces. RFC 1521 defines the use of Content-Type:
     message/partial. Support of the message/partial content type for
     use in Internet EDI is optional.

     The receiving UA is required to  re-assemble the original message
     before sending the message disposition notification to the
     original sender of the message. A message disposition notification
     is used to specify the disposition of the entire message that was
     sent, and should not be returned by a processing UA until the
     entire message is received, even if the received message requires
     re-assembling.

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

     Applying compression before encryption strengthens cryptographic
     security since repetitious strings are reduced.  This sequence is
     consistent with the PGP sequence as well.

     4.4.3 Example

     The following is an example of a signed receipt returned by a UA
     after processing a MIME EDI content type that was signed.

     NOTE: This example is provided as an illustration only, and is
     not considered part of the protocol specification. If an example
     conflicts with the protocol definitions specified above or in the
     other referenced RFCs, the example is wrong.

To:             <recipient email>
Subject:
From:           <sender email>
Date:           <date>
Mime-Version:   1.0
Content-Type: multipart/signed; boundary="separator";
    micalg=rsa-md5; protocol="application/x-pkcs7-mime"

--separator
      &Content-Type:  multipart/report;  report-type=disposition
      &       notification;  boundary = "xxxxx"
      &
      &--xxxxx
      &    The message sent to Edi Recipient <Edi_Recipient@edicorp.com>
      &    has been received, the EDI Interchange was succesfully
      &    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:  autoprocessed
      &    X-Received-MIC:   Q2hlY2sgSW50XwdyaXRIQ……
      &
      &--xxxxx
      &    Content-Type:   message/rfc822
      &
      &--xxxxx--
--separator
    Content-Type: application/x-pkcs7-mime

@ContentType = SignedData
@version = Version
@digestAlgorithms = DigestAlgorithmIdentifiers
@contentType = Data
@content =

    fgfjhHjhJhgljhgJGHGJHGJHJHJhghjhJHJuytIYTiutTYT34553//YRytdhfFFQere
    /876JHJHGIUIUgsdIUYgYTRdgggguytUTIUlbXssfdsfdREWrewREWREEWE88POF/DF
    frtFFKFG+GFff=
    =ndaj

@signerInfos = SignerInfo
--separator--

Notes:

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

-The text preceeded by "@" indicates PKCS#7 defined fields and types.
(See PKCS#7:Cryptographic Message Syntax Standard from RSA Labs, Inc.)

As specified by RFC 1892, returning the original message is not
necessary. This is an optional body part. It is recommended that
the received headers be placed in the third body part, as it can
be helpful in tracking problems.


5.   Public key certificate handling

     5.1 Near term approach

     In the near term, the exchange of public keys and certificaition
     of these keys must be handled as part of the process of
     establishing a trading partnership. The UA and/or EDI application
     interface must maintain a database of public keys used for
     encryption or signatures, in addition to the mapping between EDI
     trading partner ID and RFC822 email address. The procedures for
     establishing a trading partnership and configuring the secure EDI
     messaging system might vary among trading partners and software
     packages.

     For systems which make use of X.509 certificates, it is recommended
     that trading partners self-certify each other if an agreed upon
     certification authority is not used. It is highly recommended that
     when trading partners are using S/MIME, that they also exchange
     public key certificates using the recommendations specified in the
     S/MIME Implementation Guide Version 2. The message formats and
     S/MIME conformance requirements for certificate exchange are
     specified in this document.

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

     5.2 Long term approach

     In the long term, additional Internet-EDI standards may be
     developed to simplify the process of establishing a trading
     partnership, including the third party authentication of trading
     partners, as well as attributes of the trading relationship.


6.  Authors' Addresses

Mats Jansson
mjansson@agathon.com
LiNK
1026 Wilmington Way
Redwood City, CA 94062 USA

Chuck Shih
chucks@actracorp.com
Actra Corp.
610 East Caribbean Drive
Sunnyvale, CA 94089 USA

Nancy Turaj
nturaj@.mitre.org
MITRE Corporation
Mailstop: W657
1820 Dolley Madison Blvd.
McLean, VA 22102-3481 USA

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


7. References

[1]  N. Borenstein,  N.Freed, "MIME (Multipurpose Internet Mail
     Extensions) Part One: Mechanisms for Specifying and Describing the
     Format of Internet Message Bodies",  RFC 1521, September 23, 1993.

[2]  D. Crocker, "MIME Encapsulation of EDI Objects",  RFC 1767,  March
     2, 1995.

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

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

[5]  R. Fajman, "An Extensible Message Format for Message Disposition
     Notifications", draft-ietf-receipt-mdn-01.txt, May 13, 1996.

[6]  J. Galvin, S. Murphy, S. Crocker, N. Freed,  "Security Multiparts
     for MIME: Multipart/Signed and Multipart/Encrypted", RFC 1847, Oct.
        3,1995

[7]  J. Postel, "Simple Mail Transfer Protocol",  STD 10, RFC 821,
     August 1, 1982.

[8]  S. Dusse, "S/MIME Message Specification; PKCS Security
     Services for MIME", Internet draft: draft-dusse-mime-msg-spec
     00.txt

[9]  C. Shih, "Requirements for Inter-operable Internet EDI", July 1996.

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


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