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rfc:rfc3335

Network Working Group T. Harding Request for Comments: 3335 Cyclone Commerce Category: Standards Track R. Drummond

                                                        Drummond Group
                                                               C. Shih
                                                         Gartner Group
                                                        September 2002
                   MIME-based Secure Peer-to-Peer
            Business Data Interchange over the Internet

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

 This document describes how to exchange structured business data
 securely using SMTP transport for Electronic Data Interchange, (EDI -
 either the American Standards Committee X12 or UN/EDIFACT, Electronic
 Data Interchange for Administration, Commerce and Transport), XML or
 other data used for business to business data interchange.  The data
 is packaged using standard MIME content-types.  Authentication and
 privacy are obtained by using Cryptographic Message Syntax (S/MIME)
 or OpenPGP security body parts.  Authenticated acknowledgements make
 use of multipart/signed replies to the original SMTP message.

Harding, et. al. Standards Track [Page 1] RFC 3335 MIME-based Secure EDI September 2002

Table of Contents

 1.0   Introduction .................................................3
 2.0   Overview .....................................................4
 2.1   Purpose of a Security Guideline for MIME EDI .................4
 2.2   Definitions ..................................................4
 2.2.1 Terms ........................................................4
 2.2.2 The Secure Transmission Loop .................................5
 2.2.3 Definition of Receipts .......................................5
 2.3   Assumptions ..................................................6
 2.3.1 EDI Process Assumptions ......................................6
 2.3.2 Flexibility Assumptions ......................................7
 3.0   Referenced RFCs and Their Contribution .......................8
 3.1   RFC 821 SMTP [7] .............................................8
 3.2   RFC 822 Text Message Format [3] ..............................8
 3.3   RFC 1847 MIME Security Multiparts [6] ........................8
 3.4   RFC 1892 Multipart/Report [9] ................................8
 3.5   RFC 1767 EDI Content [2] .....................................9
 3.6   RFC 2015, 3156, 2440 PGP/MIME [4] ............................9
 3.7   RFC 2045, 2046, and 2049 MIME [1] ............................9
 3.8   RFC 2298 Message Disposition Notification [5] ................9
 3.9   RFC 2633 and 2630 S/MIME Version 3 Message Specifications [8] 9
 4.0   Structure of an EDI MIME Message - Applicability .............9
 4.1   Introduction .................................................9
 4.2   Structure of an EDI MIME Message - PGP/MIME .................10
 4.2.1 No Encryption, No Signature .................................10
 4.2.2 No Encryption, Signature ....................................10
 4.2.3 Encryption, No Signature ....................................10
 4.2.4 Encryption, Signature .......................................10
 4.3   Structure of an EDI MIME Message - S/MIME ...................10
 4.3.1 No encryption, No Signature..................................10
 4.3.2 No encryption, Signature ....................................10
 4.3.3 Encryption, No Signature ....................................11
 4.3.4 Encryption, Signature .......................................11
 5.0   Receipts ....................................................11
 5.1   Introduction ................................................11
 5.2   Requesting a Signed Receipt .................................13
 5.2.1 Additional Signed Receipt Considerations ....................16
 5.3   Message Disposition Notification Format .....................17
 5.3.1 Message Disposition Notification Extensions .................18
 5.3.2 Disposition Mode, Type, and Modifier Use ....................19
 5.4   Message Disposition Notification Processing .................21
 5.4.1 Large File Processing .......................................21
 5.4.2 Example .....................................................22
 6.0   Public Key Certificate Handling .............................24
 6.1   Near Term Approach ..........................................24
 6.2   Long Term Approach ..........................................24
 7.0   Security Considerations .....................................25

Harding, et. al. Standards Track [Page 2] RFC 3335 MIME-based Secure EDI September 2002

 8.0   Acknowledgments .............................................26
 9.0   References ..................................................26
 Appendix IANA Registration Form ...................................28
 Authors' Addresses ................................................28
 Full Copyright Statement ..........................................29

1.0 Introduction

 Previous work on Internet EDI focused on specifying MIME content
 types for EDI data ([2] RFC 1767).  This document expands on RFC 1767
 to specify use of a comprehensive set of data security features,
 specifically data privacy, data integrity/authenticity, non-
 repudiation of origin and non-repudiation of receipt.  This document
 also recognizes contemporary RFCs and is attempting to "re-invent" as
 little as possible.  While this document focuses specifically on EDI
 data, any other data type is also supported.
 With an enhancement in the area of "receipts", as described below
 (5.2), secure Internet MIME based EDI can be accomplished by using
 and complying with the following RFCs:
  1. RFC 821 SMTP
  2. RFC 822 Text Message Formats
  3. RFC 1767 EDI Content Type
  4. RFC 1847 Security Multiparts for MIME
  5. RFC 1892 Multipart/Report
  6. RFC 2015, 3156, 2440 MIME/PGP
  1. RFC 2045 to 2049 MIME RFCs
  2. RFC 2298 Message Disposition Notification
  3. RFC 2630, 2633 S/MIME v3 Specification
 Our intent here is to define clearly and precisely how these are used
 together, and what is required by user agents to be compliant with
 this document.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119.

Harding, et. al. Standards Track [Page 3] RFC 3335 MIME-based Secure EDI September 2002

2.0 Overview

2.1 Purpose of a Security Guideline for MIME EDI

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

2.2 Definitions

2.2.1 Terms

 EDI                  Electronic Data Interchange
 EC                   Electronic Commerce
 Receipt              The functional message that is sent from a
                      receiver to a sender to acknowledge
                      receipt of an EDI/EC interchange.
 Signed Receipt       Same as above, but with a digital
                      signature.
 Message Disposition  The Internet messaging format used to
 Notification         convey a receipt.  This term is used
                      interchangeably with receipt.  A signed
                      MDN is a signed receipt.
 Non-repudiation of   NRR is a "legal event" that occurs when
 Receipt (NRR)        the original sender of an EDI/EC
                      interchange has verified the signed
                      receipt coming back from the receiver.
                      NRR IS NOT a functional or a technical
                      message.
 PGP/MIME             Digital envelope security based on the
                      Pretty Good Privacy (PGP) standard
                      (Zimmerman), integrated with MIME Security
                      Multiparts [6].
 S/MIME               A format and protocol for adding
                      Cryptographic signature and/or encryption
                      services to Internet MIME messages.

Harding, et. al. Standards Track [Page 4] RFC 3335 MIME-based Secure EDI September 2002

2.2.2 The secure transmission loop

 This document's focus is on the formats and protocols for exchanging
 EDI content that has had security applied to it using the Internet's
 messaging environment.
 The "secure transmission loop" for EDI involves one organization
 sending a signed and encrypted EDI interchange to another
 organization, requesting a signed receipt, followed later by the
 receiving organization sending this signed receipt back to the
 sending organization.  In other words, the following transpires:
  1. The organization sending EDI/EC data signs and encrypts the data

using either PGP/MIME or S/MIME. In addition, the message will

    request a signed receipt to be returned to the sender of the
    message.
  1. The receiving organization decrypts the message and verifies the

signature, resulting in verified integrity of the data and

    authenticity of the sender.
  1. The receiving organization then returns a signed receipt to the

sending organization in the form of a message disposition

    notification message.  This signed receipt will contain the hash
    of the signature from the received message, indicating to the
    sender that the received message was verified and/or decrypted
    properly.
 The above describes functionality which, if implemented, would
 satisfy all security requirements.  This specification, however,
 leaves full flexibility for users to decide the degree to which they
 want to deploy those security features with their trading partners.

2.2.3 Definition of receipts

 The term used for both the functional activity and message for
 acknowledging receipt of an EDI/EC interchange is receipt, or signed
 receipt.  The first term is used if the acknowledgment is for an
 interchange resulting in a receipt which is NOT signed.  The second
 term is used if the acknowledgment is for an interchange resulting in
 a receipt which IS signed.  The method used to request a receipt or a
 signed receipt is defined in RFC 2298, "An Extensible Message Format
 for Message Disposition Notifications".
 The "rule" is:
  1. If a receipt is requested, explicitly specifying that the receipt

be signed, then the receipt MUST be returned with a signature.

Harding, et. al. Standards Track [Page 5] RFC 3335 MIME-based Secure EDI September 2002

  1. 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.
  1. If a signature is not explicitly requested, or if the signed

receipt request parameter is not recognized by the UA, a receipt

     may or may not be returned.  This behavior is consistent with the
     MDN RFC 2298.
 A term often used in combination with receipts is "Non-Repudiation of
 Receipt (NRR).  NRR refers to a legal event which occurs only when
 the original sender of an interchange has verified the signed receipt
 coming back from recipient of the message.  Note that NRR is not
 possible without signatures.

2.3 Assumptions

2.3.1 EDI Process Assumptions

  1. 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.
  1. EDI envelope headers are encrypted

Congruent with the above statement, EDI envelope headers are NOT

  visible in the MIME package.  In order to optimize routing from
  existing commercial EDI networks (called Value Added Networks or
  VANs) to the Internet, work may need to be done in the future to
  define ways to pull out some of the envelope information to make
  them visible; however, this specification does not go into any
  detail on this.
  1. X12.58 and UN/EDIFACT security considerations

The most common EDI standards bodies, ANSI X12 and EDIFACT, have

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

Harding, et. al. Standards Track [Page 6] RFC 3335 MIME-based Secure EDI September 2002

2.3.2 Flexibility Assumptions

  1. Encrypted or unencrypted data
  This specification allows for EDI message exchange where the EDI
  data can either be un-protected or protected by means of encryption.
  1. Signed or unsigned data
  This specification allows for EDI message exchange with or without
  digital signature of the original EDI transmission.
  1. Use of receipt or not
  This specification allows for EDI message transmission with or
  without a request for receipt notification.  If a signed receipt
  notification  is requested however, a mic value is REQUIRED as part
  of the returned receipt, unless an error condition occurs in which a
  mic value cannot be returned.  In error cases, an un-signed receipt
  or MDN SHOULD be returned with the correct "disposition modifier"
  error value.
  1. Formatting choices
  This specification defines the use of two methods for formatting EDI
  contents that have security applied to it:
  1. PGP/MIME
  2. S/MIME
  This specification relies on the guidelines set forth in RFC
  2015/3156/2440, as reflected in [4] "MIME Security with Pretty Good
  Privacy" (PGP); OpenPGP Message Format, and RFC 2633/2630 [8]
  "S/MIME Version 3 Message Specification; Cryptographic Message
  Syntax".  PGP/MIME or S/MIME as defined in this Applicability
  statement.
  1. Hash function, message digest choices
  When a signature is used, it is RECOMMENDED that the SHA1 hash
  algorithm be used for all outgoing messages, and that both MD5 and
  SHA1 be supported for incoming messages.
  In summary, the following eight permutations are possible in any
  given trading relationship:
  (1) Sender sends unencrypted data, does NOT request a receipt.

Harding, et. al. Standards Track [Page 7] RFC 3335 MIME-based Secure EDI September 2002

  (2) Sender sends unencrypted data, requests a signed or unsigned
      receipt.  The receiver sends back the signed or unsigned
      receipt.
  (3) Sender sends encrypted data, does NOT request a receipt.
  (4) Sender sends encrypted data, requests a signed or unsigned
      receipt.  The receiver sends back the signed or unsigned
      receipt.
  (5) Sender sends signed data, does NOT request a signed or unsigned
      receipt.
  (6) Sender sends signed data, requests a signed or unsigned receipt.
      Receiver sends back the signed or unsigned receipt.
  (7) Sender sends encrypted and signed data, does NOT request a
      signed or unsigned receipt.
  (8) Sender sends encrypted and signed data, requests a signed or
      unsigned receipt.  Receiver sends back the signed or unsigned
      receipt.
 NOTE: Users can choose any of the eight possibilities, but only
 example (8), when a signed receipt is requested, offers the whole
 suite of security features described in the "Secure transmission
 loop" above.

3.0 Referenced RFCs and Their Contribution

3.1 RFC 821 SMTP [7]

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

3.2 RFC 822 Text Message Format [3]

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

3.3 RFC 1847 MIME Security Multiparts [6]

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

3.4 RFC 1892 Multipart/report [9]

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

Harding, et. al. Standards Track [Page 8] RFC 3335 MIME-based Secure EDI September 2002

3.5 RFC 1767 EDI Content [2]

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

3.6 RFC 2015, 3156, 2440 PGP/MIME [4]

 These RFCs define the use of content types "multipart/encrypted",
 "multipart/signed", "application/pgp encrypted" and
 "application/pgp-signature" for defining MIME PGP content.

3.7 RFC 2045, 2046, and 2049 MIME [1]

 These are the basic MIME standards, upon which all MIME related RFCs
 build, including this one.  Key contributions include definition of
 "content type", "sub-type" and "multipart", as well as encoding
 guidelines, which establishes 7-bit US-ASCII as the canonical
 character set to be used in Internet messaging.

3.8 RFC 2298 Message Disposition Notification [5]

 This Internet RFC defines how a message disposition notification
 (MDN) is requested, and the format and syntax of the MDN.  The MDN is
 the basis upon which receipts and signed receipts are defined in this
 specification.

3.9 RFC 2633 and 2630 S/MIME Version 3 Message Specifications [8]

 This specification describes how MIME shall carry CMS Objects.

4.0 Structure of an EDI MIME Message - Applicability

4.1 Introduction

 The structures below are described hierarchically in terms of which
 RFC's are applied to form the specific structure.  For details of how
 to code in compliance with all RFC's involved, turn directly to the
 RFC's referenced.
 Also, these structures describe the initial transmission only.
 Receipts, and requests for receipts are handled in section 5.

Harding, et. al. Standards Track [Page 9] RFC 3335 MIME-based Secure EDI September 2002

4.2 Structure of an EDI MIME Message - PGP/MIME

4.2.1 No Encryption, No Signature

  1. RFC822/2045
    1. RFC1767 (application/EDIxxxx or /xml)

4.2.2 No Encryption, Signature

  1. RFC822/2045
    1. RFC1847 (multipart/signed)
      1. RFC1767 (application/EDIxxxx or /xml)
      2. RFC2015/2440/3156 (application/pgp-signature)

4.2.3 Encryption, No Signature

  1. RFC822/2045
    1. RFC1847 (multipart/encrypted)
      1. RFC2015/2440/3156 (application/pgp-encrypted)
        1. "Version: 1"
      2. RFC2015/2440/3156 (application/octet-stream)
        1. RFC1767 (application/EDIxxxx or /xml) (encrypted)

4.2.4 Encryption, Signature

  1. RFC822/2045
    1. RFC1847 (multipart/encrypted)
      1. RFC2015/2440/3156 (application/pgp-encrypted)
        1. "Version: 1"
      2. RFC2015/2440/3156 (application/octet-stream)
        1. RFC1847 (multipart/signed)(encrypted)
          1. RFC1767 (application/EDIxxxx or /xml)(encrypted)
          2. RFC2015/2440/3156 (application/pgp-signature)(encrypted)

4.3 Structure of an EDI MIME Message - S/MIME

4.3.1 No Encryption, No Signature

  1. RFC822/2045
    1. RFC1767 (application/EDIxxxx or /xml)

4.3.2 No Encryption, Signature

  1. RFC822/2045
    1. RFC1847 (multipart/signed)
      1. RFC1767 (application/EDIxxxx or /xml)
      2. RFC2633 (application/pkcs7-signature)

Harding, et. al. Standards Track [Page 10] RFC 3335 MIME-based Secure EDI September 2002

4.3.3 Encryption, No Signature

  1. RFC822/2045
    1. RFC2633 (application/pkcs7-mime)
      1. RFC1767 (application/EDIxxxx or /xml) (encrypted)

4.3.4 Encryption, Signature

  1. RFC822/2045
    1. RFC2633 (application/pkcs7-mime)
      1. RFC1847 (multipart/signed) (encrypted)
        1. RFC1767 (application/EDIxxxx or /xml) (encrypted)
        2. RFC2633 (application/pkcs7-signature) (encrypted)

5.0 Receipts

5.1 Introduction

 In order to support non-repudiation of receipt (NRR), a signed
 receipt, based on digitally signing a message disposition
 notification, is to be implemented by a receiving trading partner's
 UA (User Agent).  The message disposition notification, specified by
 RFC 2298 is digitally signed by a receiving trading partner as part
 of a multipart/signed MIME message.
 The following support for signed receipts is REQUIRED:
 1) The ability to create a multipart/report; where the report-type =
    disposition-notification.
 2) The ability to calculate a message integrity check (MIC) on the
    received message.  The calculated MIC value will be returned to
    the sender of the message inside the signed receipt.
 4) The ability to create a multipart/signed content with the message
    disposition notification as the first body part, and the signature
    as the second body part.
 5) The ability to return the signed receipt to the sending trading
    partner.
 The signed receipt is used to notify a sending trading partner that
 requested the signed receipt that:
 1) The receiving trading partner acknowledges receipt of the sent EDI
    Interchange.

Harding, et. al. Standards Track [Page 11] RFC 3335 MIME-based Secure EDI September 2002

 2) If the sent message was signed, then the receiving trading partner
    has authenticated the sender of the EDI Interchange.
 3) If the sent message was signed, then the receiving trading partner
    has verified the integrity of the sent EDI Interchange.
 Regardless of whether the EDI Interchange was sent in S/MIME or
 PGP/MIME format, the receiving trading partner's UA MUST provide the
 following basic processing:
 1) If the sent EDI Interchange is encrypted, then the encrypted
    symmetric key and initialization vector (if applicable) is
    decrypted using the receiver's private key.
 2) The decrypted symmetric encryption key is then used to decrypt the
    EDI Interchange.
 3) The receiving trading partner authenticates signatures in a
    message using the sender's public key.  The authentication
    algorithm performs the following:
    a) The message integrity check (MIC or Message Digest), is
       decrypted using the sender's public key.
    b) A MIC on the signed contents (the MIME header and encoded EDI
       object, as per RFC 1767) in the message received is calculated
       using the same one-way hash function that the sending trading
       partner used.
    c) The MIC extracted from the message that was sent, and the MIC
       calculated using the same one-way hash function that the
       sending trading partner used is compared for equality.
 4) The receiving trading partner formats the MDN and sets the
    calculated MIC into the "Received-content-MIC" extension field.
 5) The receiving trading partner creates a multipart/signed MIME
    message according to RFC 1847.
 6) The MDN is the first part of the multipart/signed message, and the
    digital signature is created over this MDN, including its MIME
    headers.

Harding, et. al. Standards Track [Page 12] RFC 3335 MIME-based Secure EDI September 2002

 7) The second part of the multipart/signed message contains the
    digital signature.  The "protocol" option specified in the second
    part of the multipart/signed is as follows:
    S/MIME: protocol = "application/pkcs-7-signature"
    PGP/MIME: protocol = "application/pgp-signature"
 8) The signature information is formatted according to S/MIME or
    PGP/MIME specifications.
 The EDI Interchange and the RFC 1767 MIME EDI content header, can
 actually be part of a multi-part MIME content-type.  When the EDI
 Interchange is part of a multi-part MIME content-type, the MIC MUST
 be calculated across the entire multi-part content, including the
 MIME headers.
 The signed MDN, when received by the sender of the EDI Interchange
 can be used by the sender:
 1) As an acknowledgment that the EDI Interchange sent, was delivered
    and acknowledged by the receiving trading partner.  The receiver
    does this by returning the original message id of the sent message
    in the MDN portion of the signed receipt.
 2) As an acknowledgment that the integrity of the EDI Interchange was
    verified by the receiving trading partner.  The receiver does this
    by returning the calculated MIC of the received EDI Interchange
    (and 1767 MIME headers) in the "Received-content-MIC" field of the
    signed MDN.
 3) As an acknowledgment that the receiving trading partner has
    authenticated the sender of the EDI Interchange.
 4) As a non-repudiation of receipt when the signed MDN is
    successfully verified by the sender with the receiving trading
    partner's public key and the returned mic value inside the MDN is
    the same as the digest of the original message.

5.2 Requesting a Signed Receipt

 Message Disposition Notifications are requested as per RFC 2298,
 "An Extensible Message Format for Message Disposition Notification".
 A request that the receiving user agent issue a message disposition
 notification is made by placing the following header into the message
 to be sent:

Harding, et. al. Standards Track [Page 13] RFC 3335 MIME-based Secure EDI September 2002

 MDN-request-header = "Disposition-notification-to" ":"
                       mail-address
 The mail-address field is specified as an RFC 822 user@domain
 address, and is the return address for the message disposition
 notification.
 In addition to requesting a message disposition notification, a
 message disposition notification that is digitally signed, or what
 has been referred to as a signed receipt, can be requested by placing
 the following in the message header following the "Disposition-
 Notification-To" line.
 Disposition-notification-options =
       "Disposition-Notification-Options" ":"
       disposition-notification-parameters
 where
   disposition-notification-parameters =
                     parameter *(";" parameter)
 where
   parameter = attribute "=" importance ", " 1#value"
 where
   importance = "required" | "optional"
 So the Disposition-notification-options string could be:
   signed-receipt-protocol=optional, <protocol symbol>;
   signed-receipt-micalg=optional, <micalg1>, <micalg2>,...;
 The currently supported values for <protocol symbol> are
 "pkcs7-signature", for the S/MIME detached signature format, or
 "pgp-signature", for the pgp signature format.
 The currently supported values for MIC algorithm values are:
 Algorithm   Value
 used
 MD5         md5
 SHA-1       sha1

Harding, et. al. Standards Track [Page 14] RFC 3335 MIME-based Secure EDI September 2002

 (Historical Note:  Some early implementations of EDIINT emitted and
 expected "rsa-md5" and "rsa-sha1" for the micalg parameter.)
 Receiving agents SHOULD be able to recover gracefully from a micalg
 parameter value that they do not recognize.
 An example of a formatted options line would be as follows:
 Disposition-notification-options:
   signed-receipt-protocol=optional, pkcs7-signature;
   signed-receipt-micalg=optional, sha1, md5
 The semantics of the "signed-receipt-protocol" parameter is as
 follows:
 1) The "signed-receipt-protocol" parameter is used to request a
    signed receipt from the recipient trading partner.  The
    "signed-receipt-protocol" parameter also specifies the format in
    which the signed receipt should be returned to the requester.
    The "signed-receipt-micalg" parameter is a list of MIC algorithms
    preferred by the requester for use in signing the returned
    receipt.  The list of MIC algorithms should be honored by the
    recipient from left to right.
    Both the "signed-receipt-protocol" and the "signed-receipt-micalg"
    option parameters are REQUIRED when requesting a signed receipt.
 2) The "importance" attribute of "Optional" is defined in the MDN RFC
    2298 and has the following meaning:
    Parameters with an importance of "Optional" permit a UA that does
    not understand the particular options parameter to still generate
    a MDN in response to a request for a MDN.  A UA that does not
    understand the "signed-receipt-protocol" parameter, or the
    "signed-receipt-micalg" will obviously not return a signed
    receipt.
    The importance of "Optional" is used for the signed receipt
    parameters because it is RECOMMENDED that an MDN be returned to
    the requesting trading partner even if the recipient could not
    sign it.
    The returned MDN will contain information on the disposition of
    the message as well as why the MDN could not be signed.  See the
    Disposition field in section 5.3 for more information.

Harding, et. al. Standards Track [Page 15] RFC 3335 MIME-based Secure EDI September 2002

    Within an EDI trading relationship, if a signed receipt is
    expected and is not returned, then the validity of the transaction
    is up to the trading partners to resolve.  In general, if a signed
    receipt is required in the trading relationship and is not
    received, the transaction will likely not be considered valid.

5.2.1 Additional Signed Receipt Considerations

 The "rules" stated in Section 2.2.3 for signed receipts are as
 follows:
 1) When a receipt is requested, explicitly specifying that the
    receipt be signed, then the receipt MUST be returned with a
    signature.
 2) When a receipt is requested, explicitly specifying that the
    receipt be signed, but the recipient cannot support either the
    requested protocol format, or requested MIC algorithms, then
    either a signed or unsigned receipt SHOULD be returned.
 3) When a signature is not explicitly requested, or if the signed
    receipt request parameter is not recognized by the UA, then no
    receipt, an unsigned receipt, or a signed receipt MAY be returned
    by the recipient.
 NOTE: For Internet EDI, it is RECOMMENDED that when a signature is
 not explicitly requested, or if parameters are not recognized, that
 the UA send back at a minimum, an unsigned receipt.  If a signed
 receipt however was always returned as a policy, whether requested or
 not, then any false unsigned receipts can be repudiated.
 When a request for a signed receipt is made, but there is an error in
 processing the contents of the message, a signed receipt MUST still
 be returned.  The request for a signed receipt SHALL still be
 honored, though the transaction itself may not be valid.  The reason
 for why the contents could not be processed MUST be set in the
 "disposition-field".
 When a request for a signed receipt is made, the
 "Received-content-MIC" MUST always be returned to the requester.
 The"Received-content-MIC" MUST be calculated as follows:
  1. For any signed messages, the MIC to be returned is calculated on

the RFC1767 MIME header and content. Canonicalization as specified

   in RFC 1848 MUST be performed before the MIC is calculated, since
   the sender requesting the signed receipt was also REQUIRED to
   canonicalize.

Harding, et. al. Standards Track [Page 16] RFC 3335 MIME-based Secure EDI September 2002

  1. For encrypted, unsigned messages, the MIC to be returned is

calculated on the decrypted RFC 1767 MIME header and content. The

   content after decryption MUST be canonicalized before the MIC is
   calculated.
  1. For unsigned, unencrypted messages, the MIC MUST be calculated over

the message contents prior to Content-Transfer-Encoding and without

   the MIME or any other RFC 822 headers, since these are sometimes
   altered or reordered by MTAs.

5.3 Message Disposition Notification Format

 The format of a message disposition notification is specified in RFC
 2298.  For use in Internet EDI, the following format will be used:
  1. content-type - per RFC 1892 and the RFC 2298 specification
  1. reporting-ua-field - per RFC 2298 specification
  1. MDN-gateway-field - per RFC 2298 specification
  1. original-recipient-field - per RFC 2298 specification
  1. final-recipient-field - per RFC 2298 specification
  1. original-message-id-field - per RFC 2298 specification
  1. disposition-field - the following "disposition-mode" values SHOULD

be used for Internet EDI:

   "automatic-action" - The disposition described by the disposition
                        type was a result of an automatic action,
                        rather than an explicit instruction by the
                        user for this message.
   "manual-action"    - The disposition described by the disposition
                        type was a result of an explicit instruction
                        by the user rather than some sort of
                        automatically performed action.
   "MDN-sent-automatically" - The MDN was sent because the UA had
                              previously been configured to do so.
   "MDN-sent-manually" - The user explicitly gave permission for this
                         particular MDN to be sent.
                         "MDN-sent-manually" is meaningful with
                         "manual-action", but not with
                         "automatic-action".

Harding, et. al. Standards Track [Page 17] RFC 3335 MIME-based Secure EDI September 2002

  1. disposition-field - the following "disposition-type" values SHOULD

be used for Internet EDI:

   "processed" - The message has been processed in some manner (e.g.,
                 printed, faxed, forwarded, gatewayed) without being
                 displayed to the user.  The user may or may not see
                 the message later.
   "failed" -  A failure occurred that prevented the proper generation
               of an MDN.  More information about the cause of the
               failure may be contained in a Failure field.  The
               "failed" disposition type is not to be used for the
               situation in which there is some problem in processing
               the message other than interpreting the request for an
               MDN.  The "processed" or other disposition type with
               appropriate disposition modifiers is to be used in such
               situations.
  1. disposition-field - the following "disposition-modifier" values

SHOULD be used for Internet EDI:

   "error" -  An error of some sort occurred that prevented successful
              processing of the message.  Further information is
              contained in an Error field.
   "warning" - The message was successfully processed but some sort of
               exceptional condition occurred.  Further Information is
               contained in a Warning field.

5.3.1 Message Disposition Notification Extensions

 The following "extension field" will be added in order to support
 signed receipts for RFC 1767 MIME content type and multipart MIME
 content types that include the RFC 1767 MIME content type.  The
 extension field" defined below follows the "disposition-field" in the
 MDN.
 The "Received-content-MIC" extension field is set when the integrity
 of the received message is verified.  The MIC is the base64 encoded
 quantity computed over the received message with a hash function.
 For details of "what" the "Received-content-MIC" should be calculated
 over, see Section 5.2.1.  The algorithm used to calculate the
 "Received-content-MIC" value MUST be the same as the "micalg" value
 used by the sender in the multipart/signed message.  When no
 signature is received, or the mic-alg parameter is not supported then
 it is RECOMMENDED that the SHA1 algorithm be used to calculate the
 MIC on the received message or message contents.

Harding, et. al. Standards Track [Page 18] RFC 3335 MIME-based Secure EDI September 2002

 This field is set only when the contents of the message are processed
 successfully.  This field is used in conjunction with the recipient's
 signature on the MDN in order for the sender to verify "non-
 repudiation of receipt".
  1. extension field = "Received-content-MIC" ":" MIC
   where:
   <MIC> = <base64MicValue> "," <micalg>
   <base64MicValue> = the result of one way hash function, base64
                      encoded.
   < micalg> = the micalg value defined in RFC1847, an IANA
               registered MIC algorithm ID token.

5.3.2 Disposition Mode, Type, and Modifier Use

 Guidelines for use of the "disposition-mode", "disposition-type", and
 "disposition-modifier" fields within Internet EDI are discussed in
 this section.  The "disposition-mode", "disposition-type', and
 "disposition-modifier' fields are described in detail in RFC 2298.
 The "disposition-mode', "disposition-type" and "disposition-modifier"
 values SHOULD be used as follows:

5.3.2.1 Successful Processing

 When the request for a receipt or signed receipt, and the received
 message contents are successfully processed by the receiving EDI UA,
 a receipt or MDN SHOULD be returned with the "disposition-type" set
 to there is no explicit way for a user to control the sending of the
 MDN, then the first part of the "disposition-mode" should be set to
 "automatic-action".  When the MDN is being sent under user
 configurable control, then the first part of the "disposition-mode"
 should be set to "manual-action".  Since a request for a signed
 receipt should always be honored, the user MUST not be allowed to
 configure the UA to not send a signed receipt when the sender
 requests one.
 The second part of the "disposition-mode" is set to "MDN-sent-
 manually" if the user gave explicit permission for the MDN to be
 sent.  Again, the user MUST not be allowed to explicitly refuse to
 send a signed receipt when the sender requests one.  The second part
 of the "disposition-mode" is set to "MDN-sent-automatically" whenever
 the EDI UA sends the MDN automatically, regardless of whether the
 sending was under a user's, administrator's, or under software
 control.

Harding, et. al. Standards Track [Page 19] RFC 3335 MIME-based Secure EDI September 2002

 Since EDI content is generally handled automatically by the EDI UA, a
 request for a receipt or signed receipt will generally return the
 following in the "disposition-field":
   Disposition: automatic-action/MDN-sent-automatically; processed
 Note this specification does not restrict the use of the
 "disposition-mode" to just automatic actions.  Manual actions are
 valid as long as it is kept in mind that a request for a signed
 receipt MUST be honored.

5.3.2.2 Unprocessed Content

 The request for a signed receipt requires the use of two
 "disposition-notification-options", which specify the protocol format
 of the returned signed receipt, and the MIC algorithm used to
 calculate the mic over the message contents.  The "disposition-field"
 values that should be used in the case where the message content is
 being rejected or ignored, for instance if the EDI UA determines that
 a signed receipt cannot be returned because it does not support the
 requested protocol format, so the EDI UA chooses not to process the
 message contents itself, should be specified in the MDN
 "disposition-field" as follows:
 Disposition: "disposition-mode";
   failed/Failure: unsupported format
 The syntax of the "failed" "disposition-type" is general, allowing
 the sending of any textual information along with the "failed"
 "disposition-type".  For use in Internet EDI, the following "failed"
 values are defined:
 "Failure: unsupported format" "Failure: unsupported MIC-algorithms"

5.3.2.3 Content Processing Errors

 When errors occur processing the received message content, the
 "disposition-field" should be set to the "processed" "disposition-
 type" value and the "error" "disposition-modifier" value.  For use in
 Internet EDI, the following "error" "disposition-modifier" values are
 defined:
 "Error: decryption-failed" - the receiver could not decrypt the
                              message contents.
 "Error: authentication-failed" - the receiver could not authenticate
                                  the sender.

Harding, et. al. Standards Track [Page 20] RFC 3335 MIME-based Secure EDI September 2002

 "Error: integrity-check-failed" - the receiver could not verify
                                   content integrity.
 "Error: unexpected-processing-error" - a catch-all for any additional
                                        processing errors.
 An example of how the "disposition-field" would look when content
 processing errors are detected is as follows:
 Disposition: "disposition-mode";
   processed/Error: decryption-failed

5.3.2.4 Content Processing Warnings

 Situations arise in EDI where even if a trading partner cannot be
 authenticated correctly, the trading partners still agree to continue
 processing the EDI transactions.  Transaction reconciliation is done
 between the trading partners at a later time.  In the content
 processing warning situations as described above, the "disposition-
 field" SHOULD be set to the "processed" "disposition-type" value, and
 the "warning" "disposition-modifier" value.  For use in Internet EDI,
 the following "warning" "disposition-modifier" values are defined:
 "Warning: authentication-failed, processing continued"
 An example of how the "disposition-field" would look when content
 processing warnings are detected is as follows:
 Disposition: "disposition-mode"; processed/Warning:
               authentication-failed, processing continued

5.4 Message Disposition Notification Processing

5.4.1 Large File Processing

 Large EDI Interchanges sent via SMTP can be automatically fragmented
 by some message transfer agents.  A subtype of message/partial, is
 defined in RFC 2045 [1] to allow large objects to be delivered as
 separate pieces of mail and to be automatically reassembled by the
 receiving user agent.  Using message/partial, can help alleviate
 fragmentation of large messages by different message transfer agents,
 but does not completely eliminate the problem.  It is still possible
 that a piece of a partial message, upon re-assembly, may prove to
 contain a partial message as well.  This is allowed by the Internet
 standards, and it is the responsibility of the user agent to
 reassemble the fragmented pieces.

Harding, et. al. Standards Track [Page 21] RFC 3335 MIME-based Secure EDI September 2002

 It is RECOMMENDED that the size of the EDI Interchange sent via SMTP
 be configurable so that if fragmentation is needed, then
 message/partial can be used to send the large EDI Interchange in
 smaller pieces.  RFC 2045 [1] defines the use of Content-Type:
 message/partial.
 Note: Support of the message/partial content type for use in Internet
 EDI is OPTIONAL and in the absence of knowledge that the recipient
 supports partial it SHOULD NOT be used.
 The receiving UA is required to re-assemble the original message
 before sending the message disposition notification to the original
 sender of the message.  A message disposition notification is used to
 specify the disposition of the entire message that was sent, and
 should not be returned by a processing UA until the entire message is
 received, even if the received message requires re-assembling.

5.4.2 Example

 The following is an example of a signed receipt returned by a UA
 after successfully processing a MIME EDI content type.  The sending
 trading partner has requested a return signed receipt.
 This example follows the S/MIME application/pkcs-7-signature format.
 NOTE: This example is provided as an illustration only, and is not
 considered part of the protocol specification.  If an example
 conflicts with the protocol definitions specified above or in the
 other referenced RFCs, the example is wrong.
      To: <recipient email>
      Subject:
      From: <sender email>
      Date: <date>
      Mime-Version: 1.0
      Content-Type: multipart/signed; boundary="separator";
        micalg=sha1; protocol="application/pkcs7-signature"
  1. -separator

& Content-Type: multipart/report; report-type=disposition

    &   notification;  boundary="xxxxx"
    &
    & --xxxxx
    & Content-Type: text/plain
    &
    & The message sent to Recipient <Recipient@cyclonesoftware.com>
    & has been received, the EDI Interchange was successfully
    & decrypted and its integrity was verified.  In addition, the

Harding, et. al. Standards Track [Page 22] RFC 3335 MIME-based Secure EDI September 2002

    & sender of the message, Sender <Edi_Sender@cyclonesoftware.com>
    & was authenticated as the originator of the message.  There is
    & no guarantee however that the EDI Interchange was
    & syntactically correct, or was received by the EDI
    & application.
    &
    & --xxxxx
    & Content-Type:  message/disposition-notification
    &
    & Reporting-UA: Interchange.cyclonesoftware.com (CI 2.2)
    & Original-Recipient: rfc822; Edi_Recipient@cyclonesoftware.com
    & Final-Recipient: rfc822;  Edi_Recipient@cyclonesoftware.com
    & Original-Message-ID: <17759920005.12345@cyclonesoftware.com >
    & Disposition: automatic-action/MDN-sent-automatically; processed
    & Received-content-MIC: Q2hlY2sgSW50XwdyaXRIQ, sha1
    &
    & --xxxxx
    & Content-Type: message/rfc822
    &
    & To: <recipient email>
    & Subject:
    &
    &  [additional header fields go here]
    &
    & --xxxxx--
  1. -separator

Content-Type: application/pkcs7-signature; name=smime.p7s;

      Content-Transfer-Encoding: base64
      Content-Disposition: attachment; filename=smime.p7s
      MIIHygYJKoZIhvcNAQcDoIIHuzCCB7cCAQAxgfIwge8CAQAwg
      ZgwgYMxFjAUBgNVBAMTDVRlcnJ5IEhhcmRpbmcxEDAOBgNVBA
      oTB0NZQ0xPTkUxDDAKBgNVBAsTA04vQTEQMA4GA1UEBxMHU=
  1. -separator–
 Notes:
  1. The lines preceded with "&" is what the signature is calculated

over.

  (For details on how to prepare the multipart/signed with protocol =
  "application/pkcs7-signature" see the "S/MIME Message Specification,
  PKCS Security Services for MIME".)

Harding, et. al. Standards Track [Page 23] RFC 3335 MIME-based Secure EDI September 2002

 Note: As specified by RFC 1892 [9], returning the original or
 portions of the original message in the third body part of the
 multipart/report is not required.  This is an optional body part.  It
 is RECOMMENDED that the received headers from the original message be
 placed in the third body part, as they can be helpful in tracking
 problems.
 Also note that the textual first body part of the multipart/report
 can be used to include a more detailed explanation of the error
 conditions reported by the disposition headers.  The first body part
 of the multipart/report when used in this way, allows a person to
 better diagnose a problem in detail.

6.0 Public Key Certificate Handling

6.1 Near Term Approach

 In the near term, the exchange of public keys and certification of
 these keys must be handled as part of the process of establishing a
 trading partnership.  The UA and/or EDI application interface must
 maintain a database of public keys used for encryption or signatures,
 in addition to the mapping between EDI trading partner ID and RFC 822
 [3] email address.  The procedures for establishing a trading
 partnership and configuring the secure EDI messaging system might
 vary among trading partners and software packages.
 For systems which make use of X.509 certificates, it is RECOMMENDED
 that trading partners self-certify each other if an agreed upon
 certification authority is not used.  It is highly RECOMMENDED that
 when trading partners are using S/MIME, that they also exchange
 public key certificates using the recommendations specified in the
 S/MIME Version 3 Message Specification.  The message formats and
 S/MIME conformance requirements for certificate exchange are
 specified in this document.
 This applicability statement does NOT require the use of a
 certification authority.  The use of a certification authority is
 therefore OPTIONAL.

6.2 Long Term Approach

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

Harding, et. al. Standards Track [Page 24] RFC 3335 MIME-based Secure EDI September 2002

7.0 Security Considerations

 This entire document is concerned with secure transport of business
 to business data, and considers both privacy and authentication
 issues.
 Extracted from S/MIME Version 2 Message Specification:
 40-bit encryption is considered weak by most cryptographers.  Using
 weak cryptography offers little actual security over sending plain
 text.  However, other features of S/MIME, such as the specification
 of tripleDES or AES and the ability to announce stronger
 cryptographic capabilities to parties with whom you communicate,
 allow senders to create messages that use strong encryption.  Using
 weak cryptography is never recommended unless the only alternative is
 no cryptography.  When feasible, sending and receiving agents should
 inform senders and recipients the relative cryptographic strength of
 messages.
 Extracted from S/MIME Version 2 Certificate Handling:
 When processing certificates, there are many situations where the
 processing might fail.  Because the processing may be done by a user
 agent, a security gateway, or other program, there is no single way
 to handle such failures.  Just because the methods to handle the
 failures has not been listed, however, the reader should not assume
 that they are not important.  The opposite is true:  if a certificate
 is not provably valid and associated with the message, the processing
 software should take immediate and noticeable steps to inform the end
 user about it.
 Some of the many places where signature and certificate checking
 might fail include:
  1. no certificate chain leads to a trusted CA
  2. no ability to check the CRL for a certificate
  3. an invalid CRL was received
  4. the CRL being checked is expired
  5. the certificate is expired
  6. the certificate has been revoked
 There are certainly other instances where a certificate may be
 invalid, and it is the responsibility of the processing software to
 check them all thoroughly, and to decide what to do if the check
 fails.

Harding, et. al. Standards Track [Page 25] RFC 3335 MIME-based Secure EDI September 2002

8.0 Acknowledgments

 Many thanks go out to the previous authors of the MIME-based Secure
 EDI IETF Draft:  Mats Jansson.
 The authors would like to extend special thanks to Carl Hage, Jun
 Ding, Dale Moberg, and Karen Rosenthal for providing the team with
 valuable, and very thorough feedback.  Without participants like
 those cited above, these efforts become hard to complete in a way
 useful to the users and implementers of the technology.
 In addition, the authors would like to thank Harald Alvestrand, Jim
 Galvin, and Roger Fajman for their guidance and input.

9.0 References

 [1]  Borenstein, N. and N. Freed, "Multipurpose Internet Mail
      Extensions (MIME) Part One: Format of Internet Message Bodies",
      RFC 2045, November 1996.
      Borenstein, N. and N. Freed, "Multipurpose Internet Mail
      Extensions (MIME) Part Two: Media Types", RFC 2046, November
      1996.
      Borenstein, N. and N. Freed, "Multipurpose Internet Mail
      Extensions (MIME) Part Five: Conformance Criteria and Examples",
      RFC 2049, November 1996.
 [2]  Crocker, D., "MIME Encapsulation of EDI Objects", RFC 1767,
      March 1995.
 [3]  Resnick, P., "Internet Message Format", RFC 2822, April 2001.
 [4]  Elkins, M., "MIME Security With Pretty Good Privacy (PGP)", RFC
      2015, October 1996.
      Callas, J., Donnerhacke, L., Finney, H. and R.Thayer "OpenPGP
      Message Format", RFC 2440, November 1998.
      Elkins, M., Del Torto, D., Levien, R. and T. Roessler "MIME
      Security with OpenPGP", RFC 3156, August 2001.
 [5]  Fajman, R., "An Extensible Message Format for Message
      Disposition Notifications", RFC 2298, March 1998.
 [6]  Galvin, J., Murphy, S., Crocker, S. and N. Freed,  "Security
      Multiparts for MIME: Multipart/Signed and Multipart/Encrypted",
      RFC 1847, October 1995.

Harding, et. al. Standards Track [Page 26] RFC 3335 MIME-based Secure EDI September 2002

 [7]  Klensin, J., "Simple Mail Transfer Protocol",  RFC 2821, April
      1982.
 [8]  Ramsdell, B., "S/MIME Version 3 Message Specification;
      Cryptographic Message Syntax", RFC 2633, June 1999.
      Housley, R., "Cryptographic Message Syntax", RFC 2630, June
      1999.
 [9]  Vaudreuil, G., "The Multipart/Report Content Type for the
      Reporting of Mail System Administrative Messages", RFC 1892,
      January 1996.

Harding, et. al. Standards Track [Page 27] RFC 3335 MIME-based Secure EDI September 2002

Appendix IANA Registration Form

A.1 IANA registration of the signed-receipt-protocol content

  disposition parameter
    Parameter-name: signed-receipt-protocol
    Syntax: See section 5.2 of this document
    Specification: See section 5.2 of this document

A.2 IANA registration of the signed-receipt-micalg content

  disposition parameter
    Parameter-name: signed-receipt-micalg
    Syntax: See section 5.2 of this document
    Specification: See section 5.2 of this document

A.3 IANA registration of the Received-content-MIC MDN extension

  field name
    Extension field name: Received-content-MIC
    Syntax: See section 5.3.1 of this document
    Specification: See section 5.3.1 of this document

Authors' Addresses

 Terry Harding
 Cyclone Commerce
 8388 E. Hartford Drive
 Scottsdale, Arizona 85255, USA
 EMail: tharding@cyclonecommerce.com
 Chuck Shih
 Gartner Group
 251 River Oaks Parkway
 San Jose, CA 95134-1913 USA
 EMail: chuck.shih@gartner.com
 Rik Drummond
 Drummond Group
 P.O. Box 101567
 Ft. Worth, TX 76105 USA
 EMail: rik@drummondgroup.com

Harding, et. al. Standards Track [Page 28] RFC 3335 MIME-based Secure EDI September 2002

Full Copyright Statement

 Copyright (C) The Internet Society (2002).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.  v This
 document and the information contained herein is provided on an "AS
 IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
 FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
 LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL
 NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY
 OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Harding, et. al. Standards Track [Page 29]

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