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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:
-RFC 821 SMTP
-RFC 822 Text Message Formats
-RFC 1767 EDI Content Type
-RFC 1847 Security Multiparts for MIME
-RFC 1892 Multipart/Report
-RFC 2015, 3156, 2440 MIME/PGP
-RFC 2045 to 2049 MIME RFCs
-RFC 2298 Message Disposition Notification
-RFC 2630, 2633 S/MIME v3 Specification
Our intent here is to define clearly and precisely how these are used
together, and what is required by user agents to be compliant with
this document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
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:
-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.
-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 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:
- 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
- If a receipt is requested, explicitly specifying that the receipt
be signed, but the recipient cannot support the requested
protocol format or requested MIC algorithms, then a receipt,
either signed or unsigned SHOULD be returned.
- If a signature is not explicitly requested, or if the signed
receipt request parameter is not recognized by the UA, 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
-Encrypted object is an EDI Interchange
This specification assumes that a typical EDI interchange is the
lowest level object that will be subject to security services.
In ANSI X12, this means anything between, and including segments ISA
and IEA. In EDIFACT, this means anything between, and including,
segments UNA/UNB and UNZ. In other words, the EDI interchanges
including envelope segments remain intact and unreadable during
secure transport.
-EDI envelope headers are encrypted
Congruent with the above statement, EDI envelope headers are NOT
visible in the MIME package. In order to optimize routing from
existing commercial EDI networks (called Value Added Networks or
VANs) to the Internet, work may need to be done in the future to
define ways to pull out some of the envelope information to make
them visible; however, this specification does not go into any
detail on this.
-X12.58 and UN/EDIFACT security considerations
The most common EDI standards bodies, ANSI X12 and EDIFACT, have
defined internal provisions for security. X12.58 is the security
mechanism for ANSI X12 and AUTACK provides security for EDIFACT.
This specification DOES NOT dictate use or non-use of these security
standards. They are both fully compatible, though possibly
redundant, with this specification.
Harding, et. al. Standards Track [Page 6]
RFC 3335 MIME-based Secure EDI September 2002
2.3.2 Flexibility Assumptions
-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.
-Signed or unsigned data
This specification allows for EDI message exchange with or without
digital signature of the original EDI transmission.
-Use of receipt or not
This specification allows for EDI message transmission with or
without a request for receipt notification. If a signed receipt
notification is requested however, a 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.
-Formatting choices
This specification defines the use of two methods for formatting EDI
contents that have security applied to it:
-PGP/MIME
-S/MIME
This specification relies on the guidelines set forth in RFC
2015/3156/2440, 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.
-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
-RFC822/2045
-RFC1767 (application/EDIxxxx or /xml)
4.2.2 No Encryption, Signature
-RFC822/2045
-RFC1847 (multipart/signed)
-RFC1767 (application/EDIxxxx or /xml)
-RFC2015/2440/3156 (application/pgp-signature)
4.2.3 Encryption, No Signature
-RFC822/2045
-RFC1847 (multipart/encrypted)
-RFC2015/2440/3156 (application/pgp-encrypted)
-"Version: 1"
-RFC2015/2440/3156 (application/octet-stream)
-RFC1767 (application/EDIxxxx or /xml) (encrypted)
4.2.4 Encryption, Signature
-RFC822/2045
-RFC1847 (multipart/encrypted)
-RFC2015/2440/3156 (application/pgp-encrypted)
-"Version: 1"
-RFC2015/2440/3156 (application/octet-stream)
-RFC1847 (multipart/signed)(encrypted)
-RFC1767 (application/EDIxxxx or /xml)(encrypted)
-RFC2015/2440/3156 (application/pgp-signature)(encrypted)
4.3 Structure of an EDI MIME Message - S/MIME
4.3.1 No Encryption, No Signature
-RFC822/2045
-RFC1767 (application/EDIxxxx or /xml)
4.3.2 No Encryption, Signature
-RFC822/2045
-RFC1847 (multipart/signed)
-RFC1767 (application/EDIxxxx or /xml)
-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
-RFC822/2045
-RFC2633 (application/pkcs7-mime)
-RFC1767 (application/EDIxxxx or /xml) (encrypted)
4.3.4 Encryption, Signature
-RFC822/2045
-RFC2633 (application/pkcs7-mime)
-RFC1847 (multipart/signed) (encrypted)
-RFC1767 (application/EDIxxxx or /xml) (encrypted)
-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
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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:
- 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
- For encrypted, unsigned messages, the MIC to be returned is
calculated on the decrypted RFC 1767 MIME header and content. The
content after decryption MUST be canonicalized before the MIC is
calculated.
- For unsigned, unencrypted messages, the MIC MUST be calculated over
the message contents prior to Content-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:
- content-type - per RFC 1892 and the RFC 2298 specification
- reporting-ua-field - per RFC 2298 specification
- MDN-gateway-field - per RFC 2298 specification
- original-recipient-field - per RFC 2298 specification
- final-recipient-field - per RFC 2298 specification
- original-message-id-field - per RFC 2298 specification
- disposition-field - the following "disposition-mode" values SHOULD
be used for Internet EDI:
"automatic-action" - The disposition described by the 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
- 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.
- 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".
- 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.
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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.
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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"
--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]
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& 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--
--separator
Content-Type: application/pkcs7-signature; name=smime.p7s;
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=smime.p7s
MIIHygYJKoZIhvcNAQcDoIIHuzCCB7cCAQAxgfIwge8CAQAwg
ZgwgYMxFjAUBgNVBAMTDVRlcnJ5IEhhcmRpbmcxEDAOBgNVBA
oTB0NZQ0xPTkUxDDAKBgNVBAsTA04vQTEQMA4GA1UEBxMHU=
--separator--
Notes:
-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]
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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:
- no certificate chain leads to a trusted CA
- no ability to check the CRL for a certificate
- an invalid CRL was received
- the CRL being checked is expired
- the certificate is expired
- the certificate has been revoked
There are certainly other instances where a certificate may be
invalid, and it is the responsibility of the processing software to
check them all thoroughly, and to decide what to do if the check
fails.
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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]
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Harding, et. al. Standards Track [Page 29]