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Latest revision of AS#1
I have updated the AS#1 to fold in the changes from the latest mdn
draft. Please look it over and send me comments. I am in the process of
putting the AS#1 and the Requirements document into the required RFC
format. (page numbers, form-feed, etc.) This should be done some time
next week to be submitted and posted with the IETF.
INTERNET DRAFT Chuck Shih
draft-ietf-ediint-as1-04.txt Mats Jansson, LiNK
Expires: 10 December 1997 Rik Drummond, Drummond Group
9 June 1997
MIME-based Secure EDI
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
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Abstract
This document describes how to securely exchange EDI documents
using MIME and public key cryptography.
Feedback Instructions:
If you want to provide feedback on this draft, follow these guidelines:
-Send feedback via e-mail to the ietf-ediint list for discussion, with "AS#1"
in the Subject field. To enter/follow the discussion, you need
to subscribe at ietf-ediint@xxxxxxxx
-Be specific as to what section you are referring to, preferably
quoting the portion that needs modification, after which you state
your comments.
-If you are recommending some text to be replaced with your suggested
text, again, quote the section to be replaced, and be clear on the
section in question.
Table of Contents
1. Introduction
2. Overview
2.1 Purpose of a security guideline for MIME EDI
2.2 Definitions
2.2.1 Terms
2.2.2 The secure transmission loop
2.2.3 Definition of receipts
2.3 Assumptions
2.3.1 EDI process assumptions
2.3.2 Flexibility assumptions
3. Referenced RFCs and their contribution
3.1 RFC 821 SMTP [7]
3.2 RFC 822 Text Message Format [3]
3.3 RFC 1847 MIME Security Multiparts [6]
3.4 RFC 1892 Multipart/report [9]
3.5 RFC 1767 EDI Content [2]
3.6 RFC 2015 PGP/MIME [4]
3.7 RFC 2045,2046, and 2049 MIME [1]
3.8 Internet draft (fajman): Message Disposition Notification
[5]
3.9 Internet draft (dusse): - S/MIME Specification [8]
4. Structure of an EDI MIME message - Applicability
4.1 Introduction
4.2 Structure of an EDI MIME message - PGP/MIME
4.2.1 No encryption, no signature
4.2.2 No encryption, signature
4.2.3 Encryption, no signature
4.2.4 Encryption, signature
4.3 Structure of an EDI MIME message - S/MIME
4.3.1 No encryption, no signature
4.3.2 No encryption, signature
4.3.3 Encryption, no signature
4.3.4 Encryption, signature
5. Receipts
5.1 Introduction
5.2 Requesting a signed receipt
5.2.1 Additional signed receipt considerations
5.3 Message Disposition Notification Format
5.3.1 Message Disposition Notification Extension Fields
5.3.2 Dispostion Type and Modifier Use
5.3.2.1 Successful Processing
5.3.2.2 Unprocessed Content
5.3.2.3 Content Processing Errors
5.3.2.4 Content Processing Warnings
5.4 Message Disposition Notification Processing
5.4.1 Large File Processing
5.4.2 Example
6. Public key certificate handling
6.1 Near term approach
6.2 Long term approach
7. Authors' Addresses
8. References
1. Introduction
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 these,
these efforts become hard to complete in a way useful to the users
of the technology.
The authors would also like to thank Nancy Turaj for her help
in editing portions of this document.
Previous work on Internet EDI focused on specifying MIME content
types for EDI data ([2] RFC 1767). This Applicability Statement
expands on RFC 1767 to specify use of a comprehensive set of data
security features, specifically data privacy, data
integrity/authenticity, non-repudiation of origin and non-
repudiation of receipt. This draft recognizes contemporary RFCs
and Internet drafts and is attempting to "re-invent" as little as
possible.
With an enhancement in the area of "receipts", as described below
(3.1.8), secure Internet MIME based EDI can be accomplished by
using and complying with the following RFCs and drafts:
-RFC 821 SMTP
-RFC 822 Text Message Formats
-RFC 1767 EDI Content Type
-RFC 1847 Security Multiparts for MIME
-RFC 1892 Multipart/Report
-RFC 2015 MIME/PGP (elkins)
-RFC 2045 to 2049 MIME RFCs
-Internet draft: Message Disposition Notification (fajman)
-Internet draft: S/MIME Specification (dusse)
Our intent here is to define clearly and precisely how these
are used together, and what is required by user agents to be
compliant with this Applicability Statement.
2. Overview
2.1 Purpose of a security guideline for MIME EDI
The purpose of these specifications is to ensure interoperability
between EDI user agents, invoking some or all of the commonly
expected security features. This standard is also NOT limited to
strict EDI use, but applies to any electronic commerce application
where business data needs to be exchanged over the Internet in a
secure manner.
2.2 Definitions
2.2.1. Terms
EDI Electronic Data Interchange
EC Electronic Commerce
Receipt The functional message that is sent from a
receiver to a sender to acknowledge receipt
of an EDI/EC interchange
Signed Receipt Same as above, but with a digital signature
Message Disposition The way by which a receipt or a signed
Notification (MDN) receipt is accomplished within Internet
Messaging.
Non-repudiation of NRR is a "legal event" that occurs when the
Receipt (NRR) original sender of an EDI/EC interchange has
verified the signed receipt coming back from
the receiver. NRR IS NOT a functional or a
technical message.
PGP/MIME Digital envelope security based on the Pretty
Good Privacy (PGP) standard (Zimmerman),
integrated with MIME Security Multiparts [6].
S/MIME A format and protocol for adding cryptographic
signature and/or encryption services to
Internet MIME messages.
2.2.2 The secure transmission loop
The functional requirements document, [9] "Requirements for Inter-
operable Internet EDI" (can be found at www.ietf.org),provides
extensive information on EDI security and the user/business related
processes surrounding the need for and use of EDI security. In
this document, it is assumed that the reader is familiar with the
requirements document.
This document's focus is on the formats and protocols for
exchanging EDI content that has had security applied to it using
the Internet's messaging transport.
The "secure transmission loop" for EDI involves one organization
sending a signed and encrypted EDI interchange to another
organization, requesting a "signed receipt", followed later by the
receiving organization sending this "signed receipt" back to the
sending organization. In other words, the following transpires:
-The organization sending EDI/EC data encrypts the data and
provides a digital signature, using either PGP/MIME or S/MIME.
In addition, they request a "signed receipt".
-The receiving organization decrypts the message and verifies the
signature, resulting in verified integrity of the data and
authenticity of the sender.
-The receiving organization then sends a "signed receipt" in the
form of a signature over the hash from the previous step.
The above describes functionality which if implemented, would
satisfy all security requirements. This specification, however,
leaves full flexibility for users to decide the degree to which they
want to deploy those features with their EDI trading partners.
2.2.3 Definition of receipts
The term used for both the functional activity and message for
acknowledging receipt of an EDI/EC interchange is "receipt", or
"signed receipt". The first term is used if the acknowledgment is
for an interchange resulting in a receipt which is NOT signed.
The second term is used if the acknowledgment is for an interchange
resulting in a receipt which IS signed. The "rule" is: If a receipt
is requested, explicitly specifying that the receipt be
signed, then the receipt indeed has to be returned with a signature.
If a receipt is requested, explicitly specifying that the receipt
be signed, but the recipient cannot support the requested protocol format
or requested MIC algorithms, then a receipt, either signed or unsigned should
be returned. If a signature is not explicitly requested, or if the signed receipt
request parameter is not recognized by the UA, all bets are off. This is
consistent with the MDN draft.
A term often used in combination with receipts is "Non-repudiation
of Receipt (NRR). NRR refers to a legal event which occurs only
when the original sender of an interchange has verified the sender
and content of a "signed receipt". Note that NRR is not possible
without signatures.
2.3 Assumptions
2.3.1 EDI process assumptions
-Encrypted object is an EDI Interchange
This specification assumes that a typical EDI interchange is the
lowest level object that will be subject to security features.
In ANSI X12, this means anything between, and including
segments ISA and IEA. In EDIFACT, this means anything between,
and including, segments UNA/UNB and UNZ. In other words, the
EDI interchanges including envelope segments remain intact and
unreadable during secure transport.
-EDI envelope headers are encrypted
Congruent with the above statement, EDI envelope headers are NOT
visible in the MIME package. In order to optimize VAN-to-
Internet routing, work may need to be done in the future to
define ways to pull out some of the envelope information to make
them visible, however, this specification does not go into any
detail on that.
-X12.58 and UN/EDIFACT security considerations
The most common EDI standards bodies, ANSI X12 and EDIFACT, have
defined internal provisions for security. X12.58 is the
security mechanism for ANSI X12 and AUTACK provides security for
EDIFACT. This specification DOES NOT dictate use or non-use of
these security standards. They are both fully compatible,
though possibly redundant, with this specification.
2.3.2 Flexibility assumptions
-Encrypted or un-encrypted data
This specification allows for EDI message exchange where the EDI
data is either un-protected or protected by means of encryption.
-Signed or un-signed data
This specification allows for EDI message exchange with or
without digital signature of the original EDI transmission.
-Use of receipt or not
This specification allows for EDI message transmission with or
without a request for receipt notification. If a signed receipt
notification is requested, however, a signature is required as
part of the returned receipt, unless an error condition occurs
in which a signed-receipt cannot be returned. In these cases an
un-signed receipt or MDN should be returned with the correct
"signed-receipt-disposition" value.
-Formatting choices
This specification defines use of two methods for formatting EDI
contents that have security applied to it:
-PGP/MIME
-S/MIME
This specification relies on the guidelines set forth in the
RFC 2015, as reflected in [4] MIME Security with Pretty Good
Privacy (PGP), and Internet draft [8] S/MIME Specification
from RSA Security, Inc. (dusse) Compliance with this
specification dictates that AT LEAST one of these methods is
supported.
-Hash function, message digest choices
When signature is used, unless specified otherwise by the chosen
method (PGP/MIME or S/MIME), the SHA1 checksum hash function is
recommended.
In summary, the following eight permutations are possible in
any given trading relationship:
(1) Sender sends un-encrypted data, does NOT request a receipt.
(2) Sender sends un-encrypted data, requests a receipt. Receiver
sends back a receipt.
(3) Sender sends encrypted data, does NOT request a receipt.
(4) Sender sends encrypted data, requests a receipt. Receiver
sends back a receipt.
(5) Sender sends signed data, does NOT request a signed or
un-signed receipt.
(6) Sender sends signed data, requests a signed or un-signed receipt.
Receiver sends back a signed or un-signed receipt.
(7) Sender sends encrypted and signed data, does NOT request a
signed or un-signed receipt.
(8) Sender sends encrypted and signed data, requests a signed or
un-signed receipt. Receiver sends back a signed or un-signed receipt.
NOTE: Users can choose any of the eight possibilities, but only
example (8), when a signed receipt is requested, offers the whole suite of
security features described in the "Secure transmission loop" above.
3. Referenced RFCs and their contribution
3.1 RFC 821 SMTP [7]
This is the core mail transfer standard that all MTAs need to
adhere to.
3.2 RFC 822 Text Message Format [3]
Defines message header fields and the parts making up a message.
3.3 RFC 1847 MIME Security Multiparts [6]
This document defines security multiparts for MIME:
multipart/encrypted and multipart/signed.
3.4 RFC 1892 Multipart/report [10]
This RFC defines the use of Multipart/report content type,
something that the MDN draft (fajman) relies on for the receipt
functionality.
3.5 RFC 1767 EDI Content [2]
This RFC defines the use of content type "application" for ANSI
X12 (application/EDI-X12), EDIFACT (application/EDIFACT) and
mutually defined EDI (application/EDI-Consent).
3.6 RFC 2015 PGP/MIME [4]
This RFC defines the use of content types
"multipart/encrypted", "multipart/signed", "application/pgp
encrypted" and "application/pgp-signature" for defining MIME PGP
content.
3.7 RFC 2045, 2046, and 2049 MIME [1]
These are the basic MIME standards, upon which all MIME related RFCs
build, including this one. Key contributions include definition of
"content type" and sub-type "multipart", in addition to encoding
guidelines, which establish 7-bit US-ASCII as the lowest common
denominator used.
3.8 Internet draft (fajman): Message Disposition Notification [5]
This Internet draft defines how a message disposition notification
(MDN) is requested, and the structure of the MDN.
NOTE: This is the only specification we were not able to take
"as is". Extension field-names beginning with "X-" will not be
defined as a standard field. MDN field names not beginning with "X-
" need to be registered with the Internet Assigned Numbers
Authority (IANA) and described in an RFC. The "X-" extension fields
described in this document will be registered with IANA.
3.9 Internet draft (dusse): S/MIME Message Specification [8]
This specification describes how MIME shall carry PKCS7
signature and envelope information.
4. Structure of an EDI MIME message - Applicability
4.1 Introduction
The structures below are described hierarchically in terms of which
RFC's are applied to form the specific structure. For details of
how to code in compliance with all RFC's involved, turn directly to
the RFC's referenced. The "requirements document" has several
examples described in an Appendix for those interested.
Also, these structures describe the initial transmission only.
Receipts, and requests for receipts are handled in section 5.
4.2 Structure of an EDI MIME message - PGP/MIME
4.2.1 No encryption, no signature
-RFC822/2045
-RFC1767 (application/EDIxxxx)
4.2.2 No encryption, signature
-RFC822/2045
-RFC1847 (multipart/signed)
-RFC1767 (application/EDIxxxx)
-RFC2015 (application/pgp-signature)
4.2.3 Encryption, no signature
-RFC822/2045
-RFC1847 (multipart/encrypted)
-RFC2015 (application/pgp-encrypted)
-"Version 1"
-RFC1767 (application/EDIxxxx) (encrypted)
4.2.4 Encryption, signature
-RFC822/2045
-RFC1847 (multipart/encrypted)
-RFC2015 (application/pgp-encrypted)
-"Version 1"
-RFC1767 (application/EDIxxxx) (encrypted)
-RFC2015 (application/pgp-signature) (encrypted)
4.3 Structure of an EDI MIME message - S/MIME
4.3.1 No encryption, no signature
-RFC822/2045
-RFC1767 (application/EDIxxxx)
4.3.2 No encryption, signature
-RFC822/2045
-RFC1847 (multipart/signed)
-RFC1767 (application/EDIxxxx)
-Draft (dusse) (application/x-pkcs7-signature)
4.3.3 Encryption, no signature
-RFC822/2045
-Draft (dusse) (application/x-pkcs7-mime)
-RFC1767 (application/EDIxxxx) (encrypted)
4.3.4 Encryption, signature
-RFC822/2045
-Draft (dusse) (application/x-pkcs7-mime)
-RFC1847 (multipart/signed) (encrypted)
-RFC1767 (application/EDIxxxx) (encrypted)
-Draft (dusse) (application/x-pkcs7-signature) (encrypted)
5. Receipts
5.1 Introduction
In order to support non-repudiation of receipt (NRR), a signed
receipt, based on digitally signing a message disposition notification,
is to be implemented by a receiving trading partner's UA (User Agent).
The message disposition notification, specified by draft-ietf-receipt-mdn-03.txt
is digitally signed by a receiving trading partner and returned to the
sending trading partner as part of a multipart/signed MIME message.
The required support for signed receipts when doing Internet EDI is as
follows:
1). Create a multipart/report; report-type = disposition-notification.
2). Calculate the MIC on the message disposition notification.
3). Digitally sign the MIC.
4). Create a multipart/signed content with the message disposition
notification as the first body part, and the signed MIC
calculated on the message disposition notification as the
second body part.
5). Return the signed receipt to the sending trading partner.
The signed receipt is used to notify a sending trading partner that requested
the signed receipt that:
1). The receiving trading partner acknowledges receipt of
the sent EDI Interchange.
2). If the sent message was signed, then the receiving trading
partner has authenticated the sender of the EDI Interchange.
3). If the sent message was signed, then the receiving trading
partner has verified the integrity of the received EDI Interchange.
Regardless of whether the EDI Interchange was sent in S/MIME or PGP/MIME
format, the receiving trading partner's UA must provide the following
basic processing:
1). If the sent EDI Interchange is encrypted, then the encrypted
symmetric key and initialization vector (if applicable) is
decrypted using the receiver's private key.
2). The decrypted symmetric encryption key is then used to decrypt
the EDI Interchange.
3). The receiving trading partner authenticates signatures in a
message using the sender's public key. The authentication
algorithm performs the following:
a). The message integrity check (MIC or Message Digest),
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 signature is compared with the
MIC calculated using the same one-way hash function that
the sending trading partner used.
4). The receiving trading partner formats the MDN and sets the
calculated MIC into the "X-Received-content-MIC" extension field.
5). The receiving trading partner creates a multipart/signed MIME
message according to RFC 1847.
6). The MDN is the first part of the multipart/signed message, and
the digital signature is created over this MDN, including its
MIME headers.
7). The second part of the multipart/signed message contains the
digital signature. The "protocol" option specified in the
second part of the multipart/signed is as follows:
S/MIME: protocol = "application/pkcs-7-signature"
PGP/MIME: protocol = "application/pgp-signature"
8). The signature information is formatted according to S/MIME
or PGP/MIME specifications.
The EDI Interchange and the RFC 1767 MIME EDI content header, can
actually be part of a multi-part MIME content-type. When the EDI
Interchange is part of a multi-part MIME content-type, the MIC is
calculated across the entire multi-part content, including the MIME
headers. The multi-part MIME content that contains the EDI Interchange
is then enveloped in either S/MIME or PGP/MIME format.
The signed MDN, when received by the sender of the EDI Interchange can then
be used by the sender:
1). As an acknowledgment that the EDI Interchange sent, was
delivered and acknowledged by the receiving trading partner.
The receiver does this by returning the original message
id of the sent message in the 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 "X-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 MIC calculated
over the MDN, is successfully decrypted by the sender with the
receiving trading partner's public key.
5.2 Requesting a signed receipt
Message Disposition Notifications are requested as per draft-ietf-
receipt-mdn-03.txt, "An Extensible Message Format for Message Disposition
Notification". A request that the receiving user agent issue a
message disposition notification is made by placing the following header
into the message to be sent:
mdn-request-header = "Disposition-notification-to" ":" mail-address
The mail-address field is specified as an RFC 822 user@domain address, and is
the return address for the message disposition notification.
In addition to requesting a message disposition notification, a message
disposition notification that is digitally signed, or what has been referred
to as a "signed receipt", can be requested by placing the following in the message
header following the "Disposition-notification-to" line:
Disposition-notification-options = "Disposition-notification-options" ":"
disposition-notification-parameters
Where disposition-notification-parameters = signed-receipt-protocol=O, <protocol symbol>;
signed-receipt-micalg=O, <micalg1>, <micalg2>,...;
The currently supported values for <protocol symbol> are "x-pkcs7-signature", for the
S/MIME detached signature format, or "pgp-signature", for the pgp signature format.
The signed-receipt-micalg is a list of MIC algorithm values defined in RFC1847, an IANA
registered MIC algorithm ID token.
An example of a formatted options line would be as follows:
Disposition-notification-options: signed-receipt-protocol=O, x-pkcs7-signature;
signed-receipt-micalg=O, rsa-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 requestor 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 "signed-receipts".
2). The "importance" attribute of "O" is defined in the MDN draft and has the
following meaning:
Parameters with an importance of "O" permit a UA that does not understand the
particular options parameter to still generate a MDN in response to
a request for a MDN. A UA that does not understand the "signed-receipt-protocol"
parameter, will obviously not return a signed receipt.
The importance of "O" is used for the signed receipt parameters because it
is desirable 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 and extension fields in section 5.3 for more information.
Within an EDI trading relationship, if a signed-receipt is expected and is
not returned, then the validity of the transaction is up to the trading
partners to resolve. In general, if a signed-receipt is required in the
trading relationship and is not received, the transaction will likely
not be considered valid.
5.2.1 Additional Signed Receipt Considerations
The "rules" stated in Section 2.2.3 for signed receipts are as follows:
1). When a receipt is requested, explicitly specifying that the receipt
be signed, then the receipt indeed has to 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 all bets are off.
In this situation, no receipt, an unsigned receipt, or a signed receipt
may be returned by the recipient.
NOTE: For Internet EDI, it is recommended that when a signature is not
explicitly requested, or if parameters are not recognized, that the UA
send back at a minimum, an unsigned receipt. If a signed receipt however
was always returned as a policy, whether requested or not, then any false
unsigned receipts can be repudiated.
When a request for a signed receipt is made, but there is an error in processing
the contents of the message, a signed receipt should still be returned.
The request for a signed receipt should still be honored, though the transaction
itself may not be valid. The reason for why the contents could not be processed
should still be set in the "disposition-field".
When a request for a signed receipt is made, the "X-Received-content-MIC"
should always be returned to the requestor. The "X-Received-content-MIC"
should be calculated as follows:
- For any signed messages, the MIC to be returned is calculated on the RFC1767
MIME header and content, or multipart MIME header and content. Canonicalization
as specified in RFC 1848 should be performed before the MIC is calculated,
as the sender requesting the "signed-receipt" was also required to
canonicalize.
- For encrypted, unsigned messages, the MIC to be returned is calculated on the
decrypted RFC 1767 MIME header and content, or multipart MIME header and content.
The content after decryption should be canonicalized, before the MIC is
calculated.
- For unsigned, unencrypted messages, the MIC should be calculated over the message
content prior to Content-Transfer-Encoding or Content-Encoding, and without the MIME
or any other RFC 822 headers, since these are sometimes altered or reordered by
MTAs.
5.3 Message Disposition Notification Format
The format of a message disposition notification is as specified in
draft-ietf-receipt-mdn-03.txt. For use in Internet EDI the
following format will be used:
- content-type - per RFC 1892 and the ietf-receipt-mdn specification
- reporting-ua-field - per ietf-receipt-mdn specification
- mdn-gateway-field - per ietf-receipt-mdn specification
- original-recipient-field - per ietf-receipt-mdn specification
- final-recipient-field - per ietf-receipt-mdn specification
- original-message-id-field - per ietf-receipt-mdn specification
- disposition-field - the following "disposition-type" values should be
used for EDI:
"processed" - The message has been processed in some manner
(e.g., printed, faxed, forwarded, gatewayed)
without being displayed to the user. The user may
or may not see the message later.
"failed" - A failure occurred that prevented the proper gener-
ation of an MDN. More information about the cause of
the failure may be contained in a Failure field. The
"failed" disposition type is not to be used for the
situation in which there is is some problem in
processing the message other than interpreting the
request for an MDN. The "processed" or other dis-
position type with appropriate disposition modifiers
is to be used in such situations.
- disposition-field - the following "disposition-modifier" values should be
used for EDI:
"autoaction" - 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.
"autosent" - The MDN was sent because the UA
had previously been configured to
do so automatically. "Autosent"
is meaningful with both "userac-
tion" and "autoaction".
"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 Extension Fields
The following "extension fields" will be added in order to support signed receipts for
RFC 1767 MIME content types and multi-part MIME content types that include the RFC
1767 MIME content types. The "extension fields" defined below follow the
"disposition-field" in the MDN.
The "X-Received-content-MIC" extension field is set when the integrity of the
received message is verified. The MIC is the base64 coded quantity computed over
a "body part" with a message digest or hash function. For details of "what"
the "X-Received-content-MIC" should be calculated over, see Section 5.2.1.
The algorithm used to calculate the "X-Received-content-MIC" value should be
the same as the "micalg" value received in the multipart/signed. When no signature
is received, then it is recommended that the SHA1 algorithm be used to calculate
the "X-Received-content-MIC" value.
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 "non-repudiation of receipt" to occur on the sender's
side.
- extension field = "X-" "Received-content-MIC" ":" MIC
where:
<MIC> = <base64MicValue> "," <micalg>
<hexMicValue> = the result of the one way hash function, base64
encoded.
< micalg> = the micalg value defined in RFC1847, an IANA registered
MIC algorithm ID token.
5.3.2 Disposition Type and Modifier Use
Guidelines for use of the "disposition-type" and "disposition-modifier" fields within
Internet EDI are discussed in this section. The "disposition-type" and "disposition-modifier"
fields are described in detail in draft-ietf-receipt-mdn-03.txt. For use in Internet EDI
the following "disposition-types" and "disposition-modifiers" should be used:
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 mdn should be returned
with the "disposition-type" set to "processed". When the mdn is being sent
automatically by the EDI UA, and there is no explicit way for a user to
control the sending of the mdn, then the first "disposition-modifier" should
be set to "autoaction". When the mdn is being sent under user configurable
control, then the "disposition-modifier" should be set to "useraction". Note
that a request for a "signed-receipt" should always be honored, and should
never be under user configurable or explicit control. The second "dispostion-modifier"
is set to either "usersent" when a user explicitly gives permission for the
mdn to be sent, or to "autosent" if the EDI UA had been previously configured
to send the mdn automatically. The "autosent" "disposition-modifier" is valid with
either "diposition-modifier" value "autoaction" or "useraction". The "usersent"
"dispostion-modifier" is valid only with "disposition-modifier" value "useraction".
Since EDI content is generally handled automatically by the EDI UA, a request for
a "receipt" or "signed-receipt" will return the following in the "dispostion-field":
Disposition: processed, autoaction, autosent
This specification does not however restrict the use of the "dispostion-modifier"
to just automatic actions. "Useraction" and "usersent" 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 hash over the mdn. The "disposition-field" values
that should be used in the case where the message content is being rejected or ignored,
for instance if the EDI UA determines that a "signed-receipt" cannot be returned because
it does not support the requested protocol-format, so the UA chooses not to process
the message contents itself, should be specified in the mdn "disposition-field" as
follows:
Disposition: failed, Failure: unsupported format
The syntax of the "failed" "disposition-type" is general, allowing the sending of
any textual information along with the "Failure" "disposition-modifier". For use
in Internet EDI, the following "Failure" modifier 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 take on the "processed" "disposition-type" value and the "error"
"disposition-modifier" value. For use in Internet EDI, the following "error"
"disposition-modifier" values are defined:
"Error: decryption-failed" - the receiver could not decrypt the message contents.
"Error: authentication-failed" - the receiver could not authenticate the sender.
"Error: integrity-check-failed" - the receiver could not verify content integrity.
"Error: unexpected-processing-error" - a catch-all for any additional processing errors.
An example of how the "disposition-field" would look when content processing errors
ar detected is as follows:
Disposition: 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 situation as described above, the "disposition-field"
should take on 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 errors
ar detected is as follows:
Disposition: processed, Warning: authentication-failed, processing continued
5.4 Message Disposition Notification Processing
5.4.1 Large File Processing
Large EDI Interchanges sent via SMTP can be automatically
fragmented by some message transfer agents. A subtype of message,
"partial", is defined in RFC 2045 [1] to allow large objects to be
delivered as separate pieces of mail and to be automatically
reassembled by the receiving user agent. Using message, "partial",
can help alleviate fragmentation of large messages by different
message transfer agents, but does not completely eliminate the
problem. It is still possible that a piece of a partial message,
upon re-assembly, may prove to contain a partial message as well.
This is allowed by the Internet standards, and it is
the responsibility of the user agent to re-assemble the fragmented
pieces.
It is recommended that the size of the EDI Interchange sent via
SMTP be configurable so that if fragmentation does occur, then
message, "partial" can be used to send the large EDI Interchange
in smaller pieces. RFC 2045 [1] defines the use of Content-Type:
message/partial. Support of the message/partial content type for
use in Internet EDI is optional.
The receiving UA is required to re-assemble the original message
before sending the message disposition notification to the
original sender of the message. A message disposition notification
is used to specify the disposition of the entire message that was
sent, and should not be returned by a processing UA until the
entire message is received, even if the received message requires
re-assembling.
In general, EDI content compresses well, since there is repetitive
data in most EDI Interchanges. Instead of implementing the
message/partial, compression of the EDI Interchange can be done
after the signature is applied to the EDI Interchange, and before
encryption. When no signature is applied, then compression is applied
before the encryption. Compression is an alternative solution to
implementing Content-Type: message/partial when sending large EDI
Interchanges on the Internet.
Applying compression before encryption strengthens cryptographic
security since repetitious strings are reduced. This sequence of
signature, compression, then encryption, or compression then encryption,
is consistent with the order in which PGP implementations handle compression.
Note: Compression is done automatically when using PGP encryption.
The MIME standards [1], do not define a way in which to convey
that a message has been compressed. However, RFC 2045 [1] does allow the definition
of additional MIME header fields to further describe the content of a message.
RFC 2068 [11], the HTTP/1.1 specification does define a Content-Encoding field that
is primarily used to convey compression information:
Content-Encoding = "Content-Encoding" ":" content-coding
where content-coding can take on the values of "gzip" or "compress".
The gzip compression standard is furthur described in RFC 1952 [12], and compress
is the standard UNIX file compression program. Both "gzip" and "compress" are
registered with IANA.
Trading partners can adopt the use of the Content-Encoding header if they need to
compress their EDI data and convey the compression type to their trading partners.
5.4.2 Example
The following is an example of a signed receipt returned by a UA
after successfully processing a MIME EDI content type. The sending
trading partner has requested a return signed receipt.
This example follows the S/MIME application/x-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=rsa-sha1; protocol="application/x-pkcs7-signature"
--separator
&Content-Type: multipart/report; report-type=disposition
& notification; boundary = "xxxxx"
&
&--xxxxx
&Content-Type: text/plain
&
&The message sent to Edi Recipient <Edi_Recipient@xxxxxxxxxxx>
&has been received, the EDI Interchange was successfully
&decrypted and its integrity was verified. In addition, the
&sender of the message, Edi Sender <Edi_Sender@xxxxxxxxxxxxx>
&was authenticated as the originator of the message. There is
&no guarantee however that the EDI Interchange was
&syntactically correct, or was received by the EDI
&application.
&
&--xxxxx
&Content-Type: message/disposition-notification
&
&Reporting-UA: good-edi-internet-ua.edicorp.com (ediua 1.0)
&Original-Recipient: rfc822; Edi_Recipient@xxxxxxxxxxx
&Final-Recipient: rfc822; Edi_Recipient@xxxxxxxxxxx
&Original-Message-ID: <17759920005.12345@xxxxxxxxxxx>
&Disposition: processed, autoaction, autosent
&X-Received-content-MIC: Q2hlY2sgSW50XwdyaXRIQ, rsa-sha1
&
&--xxxxx
&Content-Type: message/rfc822
&
&To: <recipient email>
&Subject:
&
& [additional header fields go here]
&
&--xxxxx--
--separator
Content-Type: application/x-pkcs7-signature
Content-Transfer-Encoding: base64
@ContentType = SignedData
@version = Version
@digestAlgorithms = DigestAlgorithmIdentifiers
@signerInfos = SignerInfo
--separator--
Notes:
-The lines preceded with "&" is what the signature is calculated
over.
-The text preceded by "@" indicates PKCS#7 defined fields and types.
(For details on how to prepare the multipart/signed with protocol
= "application/x-pkcs7-signature" see the "S/MIME Message Specification,
PKCS Security Services for MIME" documentation.)
Note: As specified by RFC 1892 [10], returning the original or portions of
the original message in the third body part of the multipart/report is not required.
This is an optional body part. It is recommended that the received headers from the
original message be placed in the third body part, as it can be
helpful in tracking problems.
Also note that the textual first body part of the multipart/report can be used
to include a more detailed explanation of the error conditions reported by the
disposition headers. The first body part of the multipart/report when used in
this way, allows a person to better diagnose a problem in detail.
6. Public key certificate handling
6.1 Near term approach
In the near term, the exchange of public keys and certification
of these keys must be handled as part of the process of
establishing a trading partnership. The UA and/or EDI application
interface must maintain a database of public keys used for
encryption or signatures, in addition to the mapping between EDI
trading partner ID and RFC 822 [3] email address. The procedures for
establishing a trading partnership and configuring the secure EDI
messaging system might vary among trading partners and software
packages.
For systems which make use of X.509 certificates, it is recommended
that trading partners self-certify each other if an agreed upon
certification authority is not used. It is highly recommended that
when trading partners are using S/MIME, that they also exchange
public key certificates using the recommendations specified in the
S/MIME Implementation Guide Version 2. The message formats and
S/MIME conformance requirements for certificate exchange are
specified in this document.
This applicability statement does NOT require the use of a
certification authority.
6.2 Long term approach
In the long term, additional Internet-EDI standards may be
developed to simplify the process of establishing a trading
partnership, including the third party authentication of trading
partners, as well as attributes of the trading relationship.
7. Authors' Addresses
Chuck Shih
chucks@xxxxxxxxxxxxx
Actra Corp.
610 East Caribbean Drive
Sunnyvale, CA 94089 USA
Mats Jansson
mjansson@xxxxxxxxxxx
LiNK
2317 Broadway, Suite 330
Redwood City, CA 94063 USA
Rik Drummond
drummond@xxxxxxxxxx
The Drummond Group
5008 Bentwood Ct.
Ft. Worth, TX 76132 USA
8. References
[1] N. Borenstein, N.Freed, "Multipurpose Internet Mail Extensions (MIME)
Part One: Format of Internet Message Bodies", RFC 2045, December 02, 1996.
N. Borenstein, N.Freed, "Multipurpose Internet Mail Extensions (MIME)
Part Two: Media Types", RFC 2046, December 02, 1996.
N. Borenstein, N.Freed, "Multipurpose Internet Mail Extensions (MIME)
Part Five: Conformance Criteria and Examples", RFC 2049 , December 02,
1996.
[2] D. Crocker, "MIME Encapsulation of EDI Objects", RFC 1767, March
2, 1995.
[3] D. Crocker, "Standard for the Format of ARPA Internet Text
Messages", STD 11, RFC 822, August 13, 1982.
[4] M. Elkins, "MIME Security With Pretty Good Privacy (PGP)", RFC
2015, Sept. 1996.
[5] R. Fajman, "An Extensible Message Format for Message Disposition
Notifications", draft-ietf-receipt-mdn-03.txt, April 6, 1997.
[6] J. Galvin, S. Murphy, S. Crocker, N. Freed, "Security Multiparts
for MIME: Multipart/Signed and Multipart/Encrypted", RFC 1847, Oct.
3, 1995
[7] J. Postel, "Simple Mail Transfer Protocol", STD 10, RFC 821,
August 1, 1982.
[8] S. Dusse, "S/MIME Message Specification; PKCS Security
Services for MIME", Internet draft: draft-dusse-mime-msg-spec
00.txt
[9] C. Shih, "Requirements for Inter-operable Internet EDI", January 1997.
[10] G. Vaudreuil, "The Multipart/Report Content Type for the Reporting
of Mail System Administrative Messages", RFC 1892, January 15,
1996.
[11] R. Fielding, J.Gettys, J. Mogul, H. Frystyk, T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2068, January 1997.
[12] L. Deutsch, "GZIP File Format Specification Version 4.3", RFC 1952,
May 23, 1996.