Network Working Group T. Harding
Request for Comments: 4823 R. Scott
Category: Informational Axway
April 2007 FTP Transport for Secure Peer-to-Peer
Business Data Interchange over the Internet
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright (C) The IETF Trust (2007).
This Applicability Statement (AS) describes how to exchange
structured business data securely using the File Transfer Protocol
(FTP) for XML, Binary, Electronic Data Interchange (EDI - ANSI X12 or
UN/EDIFACT), or other data used for business-to-business data
interchange for which MIME packaging can be accomplished using
standard MIME content types. Authentication and data confidentiality
are obtained by using Cryptographic Message Syntax (S/MIME) security
body parts. Authenticated acknowledgements employ multipart/signed
replies to the original message.
Previous work on Internet EDI focused on specifying MIME content
types for EDI data  and extending this work to support secure
EC/EDI transport over SMTP . This document expands on RFC 1767 to
specify a comprehensive set of data security features, specifically,
data privacy, data integrity, authenticity, non-repudiation of
origin, and non-repudiation of receipt over FTP. This document also
recognizes contemporary RFCs and is attempting to "re-invent" as
little as possible. While this document focuses on EDI data, any
other data type describable in a MIME format is also supported.
Internet MIME-based EDI can be accomplished by using and complying
with the following documents:
- RFC 959: File Transfer Protocol
- RFC 2228: FTP Security Extensions
- RFC 1767: EDI Content Type
- RFC 3023: XML Media Types
- RFC 1847: Security Multiparts for MIME
- RFC 3462: Multipart/Report
- RFCs 2045 to 2049: MIME
- RFC 3798: Message Disposition Notification
- RFCs 3850, 3851, and 3852: S/MIME v3.1 Specifications
- RFC 3274: Compressed Data Content for Cryptographic Message
- RFC 4217: Securing FTP with TLS
- "Compressed Data for EDIINT" by T. Harding
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
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 .
2.1. Overall Operations
An FTP upload operation is used to send appropriately packaged EDI,
XML, or other business data. The receiving application will poll the
FTP server for inbound messages, unpackage and handle the message
data, and generate a reply for the originator that contains a message
disposition acknowledgement within a multipart/report that is signed
or unsigned. This request/reply transactional interchange provides
secure, reliable, and authenticated transport for EDI or other
business data using FTP. The security protocols and structures used
also support auditable records of these transmissions.
2.2. Purpose of a Security Guideline for MIME EDI
The purpose of these specifications is to ensure interoperability
between B2B Electronic Commerce 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.
AS3 Applicability Statement 3. This is the third
applicability statement produced by the IETF
EDIINT working group.
EDI Electronic Data Interchange
EC Business-to-Business Electronic Commerce
B2B Business to Business
Receipt The functional message that is sent from a
receiver to a sender to acknowledge receipt of
an EDI/EC interchange.
Signed Receipt A receipt containing a digital signature.
Message Disposition The Internet messaging format used to convey a
Notification (MDN) receipt. This term is used interchangeably with
receipt. An MDN is a receipt.
Non-repudiation of NRR is a "legal event" that occurs when the
receipt (NRR) original sender of an EDI/EC interchange has
verified the signed receipt coming back from the
receiver. NRR IS NOT a functional or a
S/MIME A format and protocol for adding Cryptographic
signature and/or encryption services to Internet
NOTE: While the S/MIME specification describes
more than one format for a signed message,
all signed messages or receipts used with
AS3 MUST utilize the multipart/signed
SHA-1 A secure, one-way hash algorithm used in
conjunction with digital signature. SHA-1 is
the recommend algorithm for AS3.
MD5 A secure, one-way hash algorithm used in
conjunction with digital signature. This
algorithm is acceptable but not recommended due
to its short key length and known weaknesses.
MIC The message integrity check (MIC) is a
representation of the message digest, which
results from the application of the selected
hash algorithm to the content to be signed. Of
particular interest is the digital signature,
which includes an encrypted copy of the digest.
Additionally, an MDN containing a Received-
content-MIC header will also contain (as that
header's value) a base-64-encoded representation
of the digest.
User Agent (UA) The application that handles and processes the
STL Secure Transmission Loop, described in the next
2.3.2. The Secure Transmission Loop
This document's focus is on the formats and protocols for exchanging
EDI/EC content to which security services have been applied using the
File Transmission Protocol (FTP) as the transport.
The "Secure Transmission Loop" (STL) comprises the following two
a) The originator sends a signed and encrypted document with a
request for a signed receipt.
b) The recipient decrypts the document, verifies the signature, and
returns a signed receipt to the sender.
In other words, the following events occur during the execution of
- The organization sending EDI/EC data signs and encrypts the data
using 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, as
requested to the sending organization in the form of a message
disposition notification. 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
The above describes functionality that, if implemented, will satisfy
all security requirements and provide non-repudiation of receipt for
the exchange. While trading partners will usually want to utilize
the STL, this specification does not require it.
2.3.3. Definition of Receipts
The term used for both the functional activity and the message for
acknowledging delivery of an EDI/EC interchange is "receipt" or
"signed receipt". The term receipt is used if the acknowledgment is
for an interchange resulting in a receipt that is NOT signed. The
term signed receipt is used if the acknowledgment is for an
interchange resulting in a receipt that IS signed. A term often used
in combination with receipts is non-repudiation of receipt. NRR
refers to a legal event that occurs only when the original sender of
an interchange has verified the signed receipt coming back from the
recipient of the message. Note that NRR is not possible without
For additional information on formatting and processing receipts in
AS3, refer to Section 7.
2.4. Operational Assumptions and Options
2.4.1. EDI/EC Process Assumptions
- Encrypted object is an EDI/EC Interchange.
This specification assumes that a typical EDI/EC interchange is the
lowest level object that will be subject to the application of
Specifically, for EDI ANSI X12, the entire document (including the
ISA and IEA segments) is the atom to which security is applied.
For EDIFACT, the corresponding definition includes the segments
UNA/UNB and UNZ. In other words, EDI/EC interchanges including
envelope segments remain intact and unreadable during secure
- 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 extract some elements of the envelope to make them
visible; however, that is beyond the scope of this specification.
- 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.
2.4.2. Process Options
18.104.22.168. Security Options
- Encrypted or un-encrypted data
This specification allows for EDI/EC message exchange where the
EDI/EC data can be either un-protected or protected by means of
- Signed or unsigned data
This specification allows for EDI/EC message exchange with or
without digital signature of the original EDI transmission.
- Use of receipt or not
This specification allows for EDI/EC 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 that
results in the inability to compute a valid digest. (Such a case
would result, for instance, if an encrypted message could not be
decrypted.) Under such circumstances, an unsigned receipt (MDN)
SHOULD be returned with the correct "disposition modifier" error
- Security formatting
This specification relies on the guidelines set forth in RFCs 3852
 and 3851 . The first of these RFCs describes the
Cryptographic Message Syntax (CMS), and the second contains the
S/MIME Version 3.1 Message Specification describing a MIME
container for CMS objects. Whenever the term S/MIME is used in
this document, it refers to Version 3.1 as described therein.
- Hash function, message digest choices
When a signature is used, it is RECOMMENDED that the SHA-1 hash
algorithm be used for all outgoing messages; however, both MD5 and
SHA-1 MUST be supported for incoming messages.
- Permutation summary
In summary, the following twelve security 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 an unsigned receipt.
The receiver sends back the unsigned receipt.
3. Sender sends un-encrypted data, requests a signed receipt. The
receiver sends back the signed receipt.
4. Sender sends encrypted data, does NOT request a receipt.
5. Sender sends encrypted data, requests an unsigned receipt. The
receiver sends back the unsigned receipt.
6. Sender sends encrypted data, requests a signed receipt. The
receiver sends back the signed receipt.
7. Sender sends signed data, does NOT request a receipt.
8. Sender sends signed data, requests an unsigned receipt.
Receiver sends back the unsigned receipt.
9. Sender sends signed data, requests a signed receipt. Receiver
sends back the signed receipt.
10. Sender sends encrypted and signed data, does NOT request a
11. Sender sends encrypted and signed data, requests an unsigned
receipt. Receiver sends back the unsigned receipt.
12. Sender sends encrypted and signed data, requests a signed
receipt. Receiver sends back the signed receipt. This case
represents the Secure Transmission Loop described above.
22.214.171.124. Compression Options
The AS3 specification supports compression of transmitted data
directly through the application of RFC 3274. Implementation details
may be found in that RFC and in Harding's document, "Compressed Data
3. Referenced RFCs and Their Contribution
3.1. RFC 959: File Transfer Protocol 
RFC 959 specifies how data is transferred using the File Transfer
3.2. RFC 2228: FTP Security Extensions 
This RFC describes a framework for providing security services to
3.3. RFC 1847: MIME Security Multiparts 
This document defines security multiparts for MIME:
multipart/encrypted and multipart/signed.
3.11. RFC 3023: XML Media Types 
This RFC defines the use of content type "application" for XML. Note
that while conforming implementations SHOULD support the expanded
syntax that RFC 3023 introduces for the "+xml" suffix, no support for
external parsed entity types is anticipated (as it adds significant
complexity to signature processing).
4. Structure of an AS3 Message
The basic structure of AS3 messages comprises MIME encapsulated data
with both customary MIME headers and a few additional AS3-specific
outer headers. The structures below are described hierarchically in
terms of which RFCs have been applied to form the specific structure.
The reader is referred directly to the referenced RFCs for
Any additional restrictions imposed by this AS are specifically
discussed in the sections that follow.
4.2. Structure of an Internet EDI MIME Message
No encryption, no signature
-RFC1767/RFC2376 (application/EDIxxxx or /xml)
No encryption, signature
-RFC1767/RFC2376 (application/EDIxxxx or /xml)
Encryption, no signature
-RFC1767/RFC2376 (application/EDIxxxx or /xml)(encrypted)
-RFC1767/RFC2376 (application/EDIxxxx or /xml)(encrypted)
MDN, no signature
While all MIME content types SHOULD be supported,
the following MIME content types MUST be supported:
5. AS3-Specific Headers
5.1. AS3-From and AS3-To Headers
The AS3-From and AS3-To headers have been provided to assist the
sender and the recipient of an EC document to identify each other:
AS3-From: < AS3-name >
AS3-To: < AS3-name >
These headers contain textual values, described by the ABNF 
below, identifying the sender/receiver of a data exchange. A value
may be company specific (e.g., a Data Universal Numbering System
(DUNS) number), or it may be simply some string mutually acceptable
to both trading partners used to identify each to the other.
AS3-text = "!" / ; printable ASCII characters
%d35-91 / ; except double-quote (%d34)
%d93-126 ; or backslash (%d92)
AS3-qtext = AS3-text / SP ; allow space only in quoted text
AS3-quoted-pair = "\" DQUOTE / ; \" or
"\" "\" ; \\
AS3-quoted-name = DQUOTE 1*128( AS3-qtext /
AS3-atomic-name = 1*128AS3-text
AS3-name = AS3-atomic-name / AS3-quoted-name
Note: SP and DQUOTE are defined in [ABNF]RFC 4234.
The AS3-From header value and the AS3-To header value MUST each be an
AS3-name comprising 1 to 128 printable ASCII characters. The header
MUST NOT be folded, and the value for each of these headers is case-
The AS3-quoted-name SHOULD be used only if the AS3-name does not
conform to AS3-atomic-name.
The AS3-To and AS3-From header fields MUST be present in all AS3
messages and AS3 MDNs.
Implementations that map entities such as EDI identifiers/qualifiers
to AS3 identifiers may choose to constrain the set of AS3-To/AS3-From
text values to a subset of the full set defined above, but they may
not extend that set.
If the AS3-From or the AS3-To or the association of the two header
values is determined to be invalid or unknown to the receiving
system, the receiving system MAY respond with an unsigned MDN
containing an explanation of the error if the sending system
requested an MDN, but it is not required to return an MDN under those
5.2. AS3-Version Header
The AS3-Version header is a header that is required only if the value
of the header is not "1.0". Its purpose is to allow systems to
determine which version of this specification (should the
specification evolve over time) the sender of a document has used to
package the document. A user agent MUST NOT reject a message if the
version header is missing.
AS3-Version: 1*DIGIT . 1*DIGIT
A version header value of "1.1" indicates an implementation can
support EDIINT data compression . A user agent MUST NOT send
compressed messages to trading partners who do not use a version
header of "1.1" or greater.
6. FTP Considerations
6.1. FTP Security Requirements
FTP has long been viewed as an insecure protocol primarily because of
its use of cleartext authentication . This is addressed by RFC
2228 , and the use of one of the security mechanisms described
therein is strongly encouraged. Specifically, conforming
implementations of AS3 SHALL employ FTP client/servers that support
the AUTH command described within . While any authentication
mechanism based upon  MAY be utilized, AUTH TLS (as described in
) MUST be supported. (Note that  relies on TLS Version 1.0
, not Version 1.1 .)
6.2. Large File Transfers
Large files are handled correctly by the TCP layer. However, the
mechanism for compressing data, referenced in Section 126.96.36.199,
efficiently reduces transmission requirements for many data types
(including both XML and traditional EDI data). Additionally, some
FTP implementations support compression as well.
6.3. MIME Considerations for FTP
6.3.1. Required/Optional Headers
An AS3 message MUST contain the following outer headers:
An AS3 message OPTIONALLY MAY contain the following outer headers:
AS3-Version (assumed to be 1.0 if not present)
An AS3 message requesting a receipt MUST contain a Disposition-
Notification-To header and MAY contain a Disposition-Notification-
Options header (if the receipt is to be signed).
Additional headers MAY be present but are ignored.
FTP defines several data structures and character encodings via the
STRU[cture] and TYPE commands. AS3 requires the file-structure
(default) and the image type. The Content-Transfer-Encoding header
SHOULD NOT be used; if the header is present, it SHOULD have a value
of binary or 8-bit. The absence of this header or the use of
alternate values such as "base64" or "quoted-printable" MUST NOT
result in transaction failure. Content transfer encoding of MIME
parts within the AS3 message are similarly constrained.
6.3.3. Epilogue Must Be Empty
A MIME message containing an epilogue  SHALL NOT be used.
6.3.4. Message-Id and Original-Message-Id
Message-Id and Original-Message-Id are formatted as defined in
Section 3.6.4 of RFC 2822 : "<" id-left "@" id-right ">".
Message-Id length is a maximum of 998 characters. Message-Id SHOULD
be globally unique; id-right should be something unique to the
sending host environment (e.g., a host name). When sending a
message, always include the angle brackets. Angle brackets are not
part of the Message-Id value.
NOTE: When creating the Original-Message-Id header in an MDN, always
use the exact syntax contained in the original message: do not
strip or add "angle brackets".
7. Structure and Processing of an MDN Message
In order to support non-repudiation of receipt, a signed receipt,
based on digitally signing a message disposition notification, is to
be implemented by a receiving trading partner's UA. The message
disposition notification specified by RFC 3798 is digitally signed by
a receiving trading partner as part of a multipart/signed MIME
The following support for signed receipts is REQUIRED:
1) The ability to create a multipart/report; where the report-type =
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.
3) 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.
4) The ability to return the signed receipt to the sending trading
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 EC
2) If the sent message was signed, then the receiving trading partner
has authenticated the sender of the EC Interchange.
3) If the sent message was signed, then the receiving trading partner
has verified the integrity of the sent EC Interchange.
Regardless of whether the EDI/EC Interchange was sent in S/MIME
format or not, the receiving trading partner's UA MUST provide the
following basic processing:
1) If the sent EDI/EC 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
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
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 are 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
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 =
8) The signature information is formatted according to S/MIME
specifications. The EC Interchange and the RFC 1767 MIME EDI
content header can actually be part of a multipart MIME content
type. When the EDI Interchange is part of a multipart MIME
content type, the MIC MUST be calculated across the entire
multipart 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 was sent, and then
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 EC Interchange
(and 1767 MIME headers) in the "Received-content-MIC" field of the
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.
7.2. Message Disposition Notifications (MDN)
The AS3-MDNs are returned on a separate FTP TCP/IP connection and are
a response to an AS3 message.
The following diagram illustrates the delivery of an AS3-MDN
[S] ----( connect )----> [R] [FTP Server]
[S] ----( send )-------> [R] [AS3-Message]
[S] ----( disconnect )-> [R] [FTP Server]
[S] <---( connect )----- [R] [FTP Server]
[S] <---( send )-------- [R] [AS3-MDN]]
[S] <---( disconnect )-- [R] [FTP Server]
Note: Refer to Section 7.4.4 for additional
7.3. Requesting a Signed Receipt
Message Disposition Notifications are requested as per RFC 3798. 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" ":" ftpurl
This syntax is a residual of the use of MDN's in an SMTP transfer.
Since this specification is adjusting the functionality from SMTP to
FTP and retaining as much as possible from the  functionality, the
ftpurl must be present.
The ftpurl field is specified as an RFC 1738 <URL:"ftp://" login [
"/" fpath [ ";type=" ftptype ]]>, and while it MUST be present, it
may be ignored if the ftpurl points to an unknown location. If the
ftpurl points to an unknown location, it is RECOMMENDED that the mdn
is returned back to a known ftpurl for the sender of the received
For requesting MDN-based receipts, the originator supplies the
required extension headers that precede the message body.
The header "tags" are as follows:
A Disposition-notification-to header is added to indicate that a
message disposition notification is requested. This header is
specified in .
A Message-ID header is added to support message reconciliation, so
that an Original-Message-Id value can be returned in the body part of
Other headers, especially "Date", SHOULD be supplied; the values of
these headers are often mentioned in the human-readable section of an
MDN to aid in identifying the original message.
Disposition-notification-options identifies characteristics of the
The following Disposition notification is in accordance with .
Disposition-notification-to: // Requests the MDN
ftp://host:port/inbox // Location to return MDN
Disposition-notification-options: // The signing options for
signed-receipt-micalg=optional, sha1, md5
parameter *(";" parameter)
parameter = attribute "=" importance ", " value *("," value)
importance = "required" / "optional"
attribute = "signed-receipt-protocol" / "signed-receipt-micalg"
So the Disposition-notification-options string could be:
signed-receipt-protocol=optional, <protocol symbol>;
signed-receipt-micalg=optional, <micalg1>, <micalg2>,...;
The currently supported value for <protocol symbol> is "pkcs7-
signature" for the S/MIME detached signature format.
The currently supported values for MIC algorithm <micalg> values are:
Receiving agents SHOULD be able to recover gracefully from a <micalg>
parameter value that they do not recognize.
The semantics of the "signed-receipt-protocol" parameter is as
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
and calculating the micalg in the Received-content-MIC header.
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 RFC 3798,
Section 2.2, 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
an MDN in response to a request for an MDN. A UA that does not
understand the "signed-receipt-protocol" parameter, or the
"signed-receipt-micalg" parameter, will obviously not return a
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
The returned MDN will contain information on the disposition of
the message as well as on why the MDN could not be signed. See
the Disposition field in Section 7.5 for more information.
Within an EDI trading relationship, if a signed receipt is expected
and is not returned, then the validity of the transaction must be
determined by the trading partners. Typically, if a signed receipt
is required by the trading relationship and is not received, the
transaction will likely not be considered valid.
7.3.1. Signed Receipt Considerations
The method used to request a receipt or a signed receipt is defined
in RFC 3798, "An Extensible Message Format for Message Disposition
The "rules" for processing a receipt-request follow:
1) When a receipt is requested, explicitly specifying that the
receipt be signed, then the receipt MUST be returned with a
signature unless conditions (2) or (3) below are applicable.
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 receipt is requested, explicitly specifying that the
receipt be signed, but the recipient is unable to compute the
digest (e.g., message was encrypted, and recipient unable to
decrypt), then the recipient SHOULD NOT return "Received-content-
MIC" in the MDN to the requestor. If the MDN sets the disposition
(e.g., "processed/error: decryption-failed") appropriately, then
the "Received-content-MIC" may be returned, but the value must be
4) 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.
5) If a message is received without a request for a receipt, then a
receipt (signed or unsigned) MAY be returned.
The "Received-content-MIC" MUST be calculated as follows:
- For any signed messages, the MIC to be returned is calculated on
the RFC 1767 MIME header and content. Canonicalization as
specified in RFC 1848 MUST be performed before the MIC is
calculated, since the sender requesting the signed receipt was
also REQUIRED to canonicalize.
- For encrypted, unsigned messages, the MIC to be returned is
calculated on the decrypted RFC 1767 MIME header and content.
The content after decryption MUST be canonicalized before the
MIC is calculated.
- For unsigned, un-encrypted 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 message transfer agents
7.4. MDN Format and Value
This section defines the format of the AS3 Message Disposition
7.4.1. AS3-MDN General Formats
The AS3-MDN follows the MDN specification  except where noted in
this section. The modified entity definitions in this document use
the vertical-bar character, '|', to denote a logical "OR"
construction. Refer to RFC 2045 for the format of MIME-message-
The format of the AS3-MDN is
MDN, no signature
7.4.2. AS3-MDN Construction
The AS3-MDN-body is formatted as a MIME multipart/report with a
report-type of "disposition-notification".
When unsigned, the transfer-layer ("outermost") entity-headers of the
AS3-MDN contain the Content-Type header that specifies a content type
of "multipart/report", parameters indicating the report-type, and the
value of the outermost multipart boundary.
When the AS3-MDN is signed, the transfer-layer ("outermost") entity-
headers of the AS3-MDN contain a Content-Type header that specifies a
content type of "multipart/signed", parameters indicating the
algorithm used to compute the message digest, the signature
formatting protocol (e.g., pkcs7-signature), and the value of the
outermost multipart boundary. The first part of the MIME
multipart/signed message is an imbedded MIME multipart/report of type
"disposition-notification". The second part of the multipart/signed
message contains a MIME application/pkcs7-signature message.
The first part of the MIME multipart/report is a "human-readable"
portion that contains a general description of the message
disposition. The second part of the MIME multipart/report is a
"machine-readable" portion that is defined as
[ reporting-ua-field CRLF ]
[ mdn-gateway-field CRLF ]
[ original-recipient-field CRLF ]
[ original-message-id-field CRLF ]
*( failure-field CRLF )
*( error-field CRLF )
*( warning-field CRLF )
*( extension-field CRLF )
[ AS3-received-content-MIC-field CRLF ]
It is noted that several of the optional fields defined by RFC 3798
and shown above are not relevant to a point-to-point transport such
as FTP and would not normally appear in an AS3 MDN.
7.4.3. AS3-MDN Fields
The rules for constructing the AS3-disposition-notification-content
are identical to the rules for constructing the disposition-
notification-content as defined in Section 7 of RFC 3798  except
that the RFC 3798 disposition-field has been replaced with the AS3-
disposition-field and that the AS3-received-content-MIC field has
been added. The differences between the RFC 3798 disposition-field
and the AS3-disposition-field are described below. Where there are
differences between this document and RFC 3798, those entity names
have been changed by prepending "AS3-". Entities below that do not
differ from RFC 3798 are not necessarily further defined in this
Refer to RFC 3798  and RFC 4234  for entities that are not
further defined in this document.
AS3-disposition-field = "Disposition:" disposition-mode ";"
AS3-disposition-type [ "/" AS3-disposition-modifier]
disposition-mode = action-mode "/" sending-mode
action-mode = "manual-action" / "automatic-action"
sending-mode = "MDN-sent-manually" / "MDN-sent-automatically"
AS3-disposition-type = "processed" / "failed"
AS3-disposition-modifier = ( "error" / "warning" ) /
"error: authentication-failed" /
"error: decompression-failed" /
"error: decryption-failed" /
"error: insufficient-message-security" /
"error: integrity-check-failed" /
"error: unexpected-processing-error" /
"warning: " AS3-MDN-warning-description /
"failure: " AS3-MDN-failure-description
AS3-MDN-warning-description = *( TEXT )
AS3-MDN-failure-description = *( TEXT )
"," digest-alg-id CRLF
1*( ALPHA / DIGIT / "/" / "+" ) *3"="
;( i.e. base64( message-digest ) )
digest-alg-id = "sha1" / "md5"
The "Received-content-MIC" extension field is set after the integrity
of the received message is verified. The MIC is the base64-encoded
message-digest computed over the received message with a hash
function. This field is required for signed receipts but optional
for unsigned receipts. For details defining the specific content
over which the message-digest is to be computed, see Section 7.3.1 of
The algorithm used to calculate the message digest MUST be the same
as the "micalg" value used by the sender in the multipart/signed
message. When no signature is received, the message-digest MUST be
calculated using the algorithm specified by the "micalg" value in the
Disposition-Notification-Options header. When no signature is
received and no micalg parameter is provided, then the SHA-1
algorithm MUST be used to calculate the digest. 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.
AS3-MDN field names (e.g., "Disposition:", "Final-Recipient:") are
case-insensitive (cf. RFC 3798, Section 3.1.1).
AS3-MDN action-modes, sending-modes, AS3-disposition-types, and AS3-
disposition-modifier values that are defined above, and user-supplied
*( TEXT ) values are also case-insensitive. AS3 implementations MUST
NOT make assumptions regarding the values supplied for AS3-MDN-
warning-description or AS3-MDN-failure-description or for the values
of any (optional) error, warning, or failure fields.
7.4.4. Additional AS3-MDN Programming Notes
1. Unlike SMTP, for FTP transactions, Original-Recipient and Final
Recipient SHOULD NOT be different. The value in Original-
Message-ID MUST match the original Message-ID header value.
2. Refer to RFC 3462 and RFC 3798 for the formatting of the
Content-Type entity-headers for the MDN.
3. Use an action-mode of "automatic-action" when the disposition
described by the disposition type was a result of an automatic
action, rather than an explicit instruction by the user for this
4. Use an action-mode of "manual-action" when the disposition
described by the disposition type was a result of an explicit
instruction by the user rather than some sort of automatically
5. Use a sending-mode of "MDN-sent-automatically" when the MDN is
sent because the UA had previously been configured to do so.
6. Use a sending-mode of "MDN-sent-manually" when the user
explicitly gave permission for this particular MDN to be sent.
7. The sending-mode "MDN-sent-manually" is ONLY meaningful with
"manual-action", not with "automatic-action".
8. The "failed" disposition type MAY NOT 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.
9. An AS3 implementation MUST present to its trading partners an
FTP-compliant server interface where inbound documents and MDNs
10. An AS3 implementation MUST be able to retrieve inbound messages
from its currently configured FTP server interface.
Note: Programming Notes 9 and 10 do not imply any specific method for
supplying the FTP server interface. But, they do allow for
several different types of implementations. Some vendors may
choose to imbed an FTP-compliant server interface within their
product, and others may choose to utilize off-the-shelf FTP
servers to supply the required FTP server interface. Some may
choose to utilize hosting services provided by their trading
partner or by a third-party hosting service. Whichever method
is utilized, an AS3 implementation MUST support rules 9 and 10.
11. AS3 implementations MAY imbed an FTP server interface within
12. AS3 implementations MUST be configurable to allow the use of an
external FTP hosting service.
Note: An external FTP hosting service may be hosted by a third-party
or possibly hosted by your trading partner.
7.5. Disposition Mode, Type, and Modifier
7.5.1. Disposition Mode Overview
This section will provide a brief overview of how processed, error,
failure, or warning notifications are used.
7.5.2. Successful Processing Status Indication
When a receipt or signed receipt is requested, and the received
message contents are successfully processed by the receiving EDI UA,
a receipt or MDN SHOULD be returned with the "disposition-type" set
to "processed". When the MDN is sent automatically by the EDI UA,
and there is no explicit way for a user to control the sending of the
MDN, then the first part of the "disposition-mode" should be set to
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 not to 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, an administrator's, or software control.
Since EDI content is generally handled automatically by the EDI UA, a
request for a receipt or signed receipt will generally return the
following in the "disposition-field":
Disposition: automatic-action/MDN-sent-automatically; processed
Note this specification does not restrict the use of the
"disposition-mode" to just automatic actions. Manual actions are
valid as long as it is kept in mind that a request for a signed
receipt MUST be honored.
7.5.3. Unsuccessful Processed 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 should be specified in the MDN
"disposition-field" as below. (An example of this case is when 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.)
Disposition: "disposition-mode"; failed/Failure: unsupported Format
The "failed" AS3-disposition-type should be used when a failure
occurs that prevents the proper generation of an MDN.
For example, this disposition-type would apply if the sender of the
message requested the application of an unsupported message-
integrity-check (MIC) algorithm.
The "failure:" AS3-disposition-modifier-extension should be used with
an implementation-defined description of the failure.
Further information about the failure may be contained in a failure-
field. The syntax of the "failed" "disposition-type" is general,
allowing the sending of any textual information along with the
"failed" "disposition-type". Implementations WILL support any
printable textual characters after the Failure disposition-type.
For use in Internet EDI, the following "failed" values are pre-
defined and MUST be supported:
"Failure: unsupported format"
"Failure: unsupported MIC-algorithms"
7.5.4. Unsuccessful Non-Content Processing
When errors occur in processing the received message, other than
content, the "disposition-field" should be set to the "processed"
"disposition-type" value and the "error" "disposition-modifier"
The "error" AS3-disposition-modifier with the "processed"
disposition-type should be used to indicate that an error of some
sort occurred that prevented successful processing of the message.
Further information may be contained in an error-field.
An "error:" AS3-disposition-modifier-extension should be used to
combine the indication of an error with a pre-defined description of
a specific, well-known error. Further information about the error
may be contained in an error-field.
For use in Internet EDI, the following "error" "disposition-modifier"
values are defined:
The receiver could not decrypt the message contents.
The receiver could not authenticate the sender.
The receiver could not verify content integrity.
The security level of the message did not match the agreed level
The receiver could not decompress the message contents.
A catch-all for any additional processing errors.
An example of how the "disposition-field" would look when processing
errors, other than content, are detected is as follows:
7.5.5. 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 described above, the "disposition-
field" SHOULD be set to the "processed" "disposition-type" value, and
the "warning" "disposition-modifier" value.
The "warning" AS3-disposition-modifier should be used with the
"processed" disposition-type to indicate that the message was
successfully processed but that an exceptional condition occurred.
Further information may be contained in a warning-field.
A "warning:" AS3-disposition-modifier-extension should be used to
combine the indication of a warning with an implementation-defined
description of the warning. Further information about the warning
may be contained in a warning-field.
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 processing
warnings, other than content, are detected is as follows:
Disposition: "disposition-mode"; processed/Warning:
authentication-failed, processing continued
8. Public Key Certificate Handling
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 FTP
URL/URI. The procedures for establishing a trading partnership and
configuring the secure EDI messaging system might vary among trading
partners and software packages.
X.509 certificates are REQUIRED. It is RECOMMENDED that trading
partners self-certify each other if an agreed-upon certification
authority is not used. This applicability statement does NOT require
the use of a certification authority.
The use of a certification authority is therefore OPTIONAL.
Certificates may be self-signed. It is 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 3.1 Message Specification.
The message formats and S/MIME conformance requirements for
certificate exchange are specified in this document. 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.
9. Security Considerations
This entire document is concerned with secure transport of business-
to-business data, and it considers both privacy and authentication
Extracted from S/MIME Version 2 Message Specification :
40-bit encryption is considered weak by most cryptographers.
Using weak cryptography in S/MIME offers little actual security
over sending plaintext. However, other features of S/MIME, such
as the specification of tripleDES 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 3.1 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 Internet mail addresses in a certificate matches the sender
of a message, if the certificate contains at least one mail
- no certificate chain leads to a trusted CA
- no ability to check the Certificate Revocation List (CRL) for a
- 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
The following certificate types MUST be supported.
Certification Authority Certified
The complete certification chain MUST be included in all
certificates. All certificate verifications MUST "chain to root".
Additionally, the certificate hash should match the hash recomputed
by the receiver.
10.1. Normative References
 Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Five: Conformance Criteria and
Examples", RFC 2049, November 1996.
 Crocker, D., "MIME Encapsulation of EDI Objects", RFC 1767,
 Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9,
RFC 959, October 1985.
 Horowitz, M. and S. Lunt, "FTP Security Extensions", RFC 2228,
 Harding, T., Drummond, R., and C. Shih, "MIME-based Secure
Peer-to-Peer Business Data Interchange over the Internet", RFC
3335, September 2002.
 Hansen, T. and G. Vaudreuil, "Message Disposition
Notification", RFC 3798, May 2004.
 Galvin, J., Murphy, S., Crocker, S., and N. Freed, "Security
Multiparts for MIME: Multipart/Signed and Multipart/Encrypted",
RFC 1847, October 1995.
 Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
 Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852,
 Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Message Specification", RFC 3851, July
 Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Certificate Handling", RFC 3850, July
 Vaudreuil, G., "The Multipart/Report Content Type for the
Reporting of Mail System Administrative Messages", RFC 3462,
 Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
2246, January 1999.
 Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT
MESSAGES", STD 11, RFC 822, August 1982.
 Resnick, P., "Internet Message Format", RFC 2822, April 2001.
 Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
RFC 3023, January 2001.
 Gutmann, P., "Compressed Data Content Type for Cryptographic
Message Syntax (CMS)", RFC 3274, June 2002.
 Ford-Hutchinson, P., "Securing FTP with TLS", RFC 4217, October
 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
 Harding, T., "Compressed Data for EDIINT", Work in Progress,
 Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L., and L.
Repka, "S/MIME Version 2 Message Specification", RFC 2311,
 Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
 Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
Protocol Version 1.1", RFC 4346, April 2006.
Appendix A. Message Examples
NOTE: All examples are provided as an illustration only, and are not
considered part of the protocol specification. If an example
conflicts with the protocol definitions specified above or with
that of a referenced RFC, the example is wrong.
A.1. Signed Message Requesting a Signed Receipt
Date: Wed, 31 Jul 2002 13:34:50 GMT
AS3-To: "trading partner"
Content-Type: multipart/signed; boundary="as3BouNdary1as3";
Content-Disposition: Attachment; filename=rfc1767.dat
[ISA ...EDI transaction data...IEA...]
[omitted binary pkcs7 signature data]
A.2. MDN for Message A.1 Above
Date: Wed, 31 Jul 2002 13:34:50 GMT
AS3-From: "trading partner"
Content-Type: multipart/signed; micalg=sha1;
& Content-Type: multipart/report;
&MDN for -
& Message ID: <200207310834482A70BF63@host.com>
& From: cyclone
& To: "trading partner"
& Received on: 2002-07-31 at 09:34:14 (EDT)
& Status: processed
& Comment: This is not a guarantee that the message has been
& completely processed or understood by the receiving translator
& Content-Type: message/disposition-notification
& Content-Transfer-Encoding: 7bit
& Reporting-UA: AS3 Server
& Original-Recipient: rfc822; "trading partner"
& Final-Recipient: rfc822; "trading partner"
& Original-Message-ID: <200207310834482A70BF63@host.com>
& Received-content-MIC: 7v7F++fQaNB1sVLFtMRp+dF+eG4=, sha1
& Disposition: automatic-action/MDN-sent-automatically; processed
Content-Type: application/pkcs7-signature; name=smime.p7s
Content-Disposition: attachment; filename=smime.p7s
1. The lines proceeded with "&" are what the signature is
2. For details on how to prepare the multipart/signed with
protocol="application/pkcs7-signature", see RFC 3851 ,
"Secure/Multipurpose Internet Mail Extensions (S/MIME) Version
3.1 Message Specification".
3. 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.
4. As specified by RFC 3462 , 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. However, it is RECOMMENDED that this body part be
omitted or left blank.
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