A. Ward INTERNET-DRAFT Category: Experimental 15 June 2000 draft-ward-esmtp-slide-03.txt Exprires: 15 December 2000 SMTP Service Extension for Slightly Differing Multicast Messages (SLIDE) Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. i. Revision History The first version (-00) of this document was unleashed on 9 March 2000. (-01) Added section (5.1), regarding the impact of the SLIDE extension to signed or encrypted messages. Modified the first example in section (4.) to make the impact of SLIDE more explicit. (7 April 2000) (-02) Added examples to section (5.1.1) and section (5.1.2). (4 May 2000) (-03) Minor formatting changes to comply with RFC 2223. (15 June 2000) Ward [Page 1] INTERNET-DRAFT SMTP Service Extension SLIDE 15 June 2000 Abstract This memo defines an extension to the SMTP service [Klensin, et al 1995] to realize efficiency improvements in the relaying and delivery of slightly differing messages bound for more than one recipient, as specified by multiple RCPT TO commands [Postel 1982]. 0. Conventions Used in this Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [Bradner 1997]. 1. Introduction SMTP is an Internet message protocol that is used to send messages to one or more recipients. To realize any efficiency when sending a message to multiple recipients, the message body and all headers must be identical. It is desirable, under some circumstances, to send messages to multiple recipients that differ only slightly in their body and/or headers. Under SMTP [Postel 1982] such a scenario would result in a different message being sent from the initial client SMTP through each relay server until the final server SMTP is reached. In situations where more that one of the multiple recipients have mail handled by the same server SMTP, a significant bandwidth reduction can be realized with the SLIDE service extension. 2. Framework for the Slightly Differing Multicast Message Extension The slightly differing multicast message extension is as follows: (1) the name of the SMTP service extension defined here is slightly- differing-multicast-message; (2) the EHLO keyword value associated with the extension is SLIDE; (3) no parameter is used with the SLIDE EHLO keyword; (4) no additional SMTP verbs are defined by this extension (5) one optional parameter using the keyword SLIDERANGE is added to the RCPT TO command. The value associated with this parameter is a comma-delimited list of octet ranges indicating which pieces of the overall message SHOULD be delivered to the specified recipient. The syntax for the value follows, using the ABNF notation of [Crocker Ward [Page 2] INTERNET-DRAFT SMTP Service Extension SLIDE 15 June 2000 1982]: sliderange-value ::= octet-range *( "," octet-range ) octet-range ::= octet-address [ "-" octet-address ] octet-address ::= DIGIT *(DIGIT) DIGIT ::= (6) the next section specifies how support for the extension affects the behaviour of a server and client SMTP; and, (7) the maximum length of a RCPT TO command line is increased by 256 characters by the possible addition of the SLIDERANGE keyword and value. Of course, since the value could conceivably be longer than 256 characters, implementations are welcome to allot more space for this purpose. 3. The slightly-differing-multicast-message Service Extension 3.1 Effects on the Client SMTP When a client SMTP wishes to submit (using the MAIL command) messages with slightly different content to recipients at the same server SMTP, it first issues the EHLO command to the server SMTP. If the server SMTP responds with code 250 to the EHLO command, and the response includes the EHLO keyword value SLIDE, then the server SMTP is indicating that it supports the extended RCPT command. Such a server SMTP will accept a message containing the combined contents of the slightly differing messages addressed to all of the recipients for delivery. The method for combining the various message bodies (and interpreting combined message bodies) is described in the next section. The extended RCPT command is issued by a client SMTP when it wishes to transmit part of a combined message body to the specified recipient. The syntax for this command is identical to the RCPT command in [Postel 1982], except that a SLIDERANGE parameter must appear after the address. Multiple SLIDERANGE parameters may be used in a single RCPT command; however, in such a case, the values of the several parameters SHOULD be combined into a single, continuous, comma-delimited list of octet ranges. The value associated with the SLIDERANGE parameter lists which octets in the impending DATA command are to be sent to the specified recipient. Ward [Page 3] INTERNET-DRAFT SMTP Service Extension SLIDE 15 June 2000 3.2 Effects on the Server SMTP A server SMTP which supports the slightly differing multicast message service extension SHOULD relay only those octets bound for recipients at a particular domain to the mail exchange for that domain. If this suggested message trimming occurs, the octets specified in the SLIDERANGE parameter for each recipient MUST be adjusted to correspond with the changes to the message DATA. The final 5 octets of the message DATA (.) MUST always be relayed, even if not explicitly specified in the SLIDERANGE parameter value. Once a server SMTP supporting the slightly differing multicast message service extension accepts a message for which any recipient has a non-trivial SLIDERANGE parameter value, the server SMTP MUST deliver or relay the message in such a way as to ensure that only the octets specified for a particular recipient will be received by that recipient. As well, when the server SMTP is relaying the message, it SHOULD attempt to minimize the number of octets that are relayed to each downstream server SMTP. 4. Usage Examples The following dialogue illustrates the use of the slightly differing multicast message service extension: S: C: S: 220 anstruther.elsewhere.com SMTP ready C: EHLO burleigh.uwaterloo.ca S: 250-hello burleigh.uwaterloo.ca S: 250 SLIDE C: MAIL FROM: S: 250 ... sender okay C: RCPT TO: SLIDERANGE=0-148,180-322 S: 250 ... recipient and SLIDERANGE okay C: RCPT TO: SLIDERANGE=0-121,149-272,320-322 S: 250 ... recipient and SLIDERANGE okay C: DATA S: 354 octets beyond 323 will not be relayed, end with CRLF.CRLF C: Message-ID: <1234.abcd@uwaterloo.ca> C: Date: Mon, 03 Apr 2000 12:05:10 -0400 C: From: Andrew C: To: Ed C: To: Doug C: Subject: special message C: Ward [Page 4] INTERNET-DRAFT SMTP Service Extension SLIDE 15 June 2000 C: this is the message body for a special message C: C: enjoy, andrew C: C: ps. this is a secret that Doug doesn't know C: . S: 250 okay C: QUIT S: 250 bye bye This transaction would result in ed@elsewhere.com receiving the message: Message-ID: <1234.abcd@uwaterloo.ca> Date: Mon, 03 Apr 2000 12:05:10 -0400 From: Andrew To: Ed Subject: special message this is the message body for a special message enjoy, andrew ps. this is a secret that Doug doesn't know . while doug@elsewhere.com would receive: Message-ID: <1234.abcd@uwaterloo.ca> Date: Mon, 03 Apr 2000 12:05:10 -0400 From: Andrew To: Doug Subject: special message this is the message body for a special message enjoy, andrew . The following dialogue illustrates the efficiencies that can be realized in a relaying scenario: S1: 220 one.there.com SMTP ready C0: EHLO zero.here.com S1: 250-hello zero.here.com S1: 250 SLIDE C0: MAIL FROM: S1: 250 ... sender okay Ward [Page 5] INTERNET-DRAFT SMTP Service Extension SLIDE 15 June 2000 C0: RCPT TO: SLIDERANGE=0-150,200-250 S1: 250 ... recipient and SLIDERANGE okay C0: RCPT TO: SLIDERANGE=0-199 S1: 250 ... recipient and SLIDERANGE okay C0: RCPT TO: SLIDERANGE=0-250 S1: 250 ... recipient and SLIDERANGE okay C0: RCPT TO: S1: 250 ... recipient okay C0: DATA S1: 354 okay, send message body, end with CRLF.CRLF C0: ...<1000 octets of message>... C0: . S1: 250 okay C0: QUIT S1: 250 bye bye ... S2: 220 two.everywhere.com SMTP ready C1: EHLO one.there.com S2: 250-hello one.there.com S2: 250 SLIDE C1: MAIL FROM: S2: 250 ... sender okay C1: RCPT TO: SLIDERANGE=0-150,200-250 S2: 250 ... recipient and SLIDERANGE okay C1: RCPT TO: SLIDERANGE=0-199 S2: 250 ... recipient and SLIDERANGE okay C1: RCPT TO: S2: 250 ... recipient okay C1: DATA S2: 354 okay, send message body, end with CRLF.CRLF C1: ...... C1: . S2: 250 okay C1: QUIT S2: 250 bye bye ... S3: 220 three.elsewhere.com SMTP ready C1: EHLO one.there.com S3: 250-hello one.there.com S3: 250 SLIDE C1: MAIL FROM: S3: 250 ... sender okay C1: RCPT TO: S3: 250 ... recipient okay C1: DATA S3: 354 okay, send message body, end with CRLF.CRLF C1: ...... C1: . Ward [Page 6] INTERNET-DRAFT SMTP Service Extension SLIDE 15 June 2000 S3: 250 okay C1: QUIT S3: 250 bye bye 5. Security Considerations This extension takes some of the "final control" over the message body out of the hands of the client, and places it on the server SMTPs that are charged with relaying and delivering the message. While any server SMTP has access to change the content of a message that it relays or delivers, a server SMTP that supports the slightly differing multicast message service extension is obliged to be able to alter a message that takes advantage of this extension. As a result of the increased handling by the server SMTP, there is more room for error in the message transmission. 5.1 Impact on Signed and Encrypted Messages Messages that are transferred between a client SMTP and a server SMTP over a secure channel such as SSL or TLS should not be adversely affected by the SLIDE extension. Things get messy when it comes to signing or encrypting the message data (all or part of the information sent to the server SMTP following a 354 response to the DATA command). Two alternatives are suggested in section (5.1.1) and section (5.1.2). A client SMTP may implement either method, as both methods can be used transparently to all other nodes in the chain of relays (including the final server SMTP node). 5.1.1 Piecewise Signing and Encryption With this method, the initial client SMTP may sign or encrypt each separate range of bytes (or part thereof), as defined by the various SLIDERANGE values. As an example, consider the piecewise approach as applied to the first usage example presented in section 4. S: C: S: 220 anstruther.elsewhere.com SMTP ready C: EHLO burleigh.uwaterloo.ca S: 250-hello burleigh.uwaterloo.ca S: 250 SLIDE C: MAIL FROM: S: 250 ... sender okay C: RCPT TO: SLIDERANGE=0-148,180-727 Ward [Page 7] INTERNET-DRAFT SMTP Service Extension SLIDE 15 June 2000 S: 250 ... recipient and SLIDERANGE okay C: RCPT TO: SLIDERANGE=0-121,149-483,725-727 S: 250 ... recipient and SLIDERANGE okay C: DATA S: 354 octets beyond 728 will not be relayed, end with CRLF.CRLF C: Message-ID: <1234.abcd@uwaterloo.ca> C: Date: Mon, 03 Apr 2000 12:05:10 -0400 C: From: Andrew C: To: Ed C: To: Doug C: Subject: special message C: C: -----BEGIN PGP SIGNED MESSAGE----- C: Hash: SHA1 C: C: this is the message body for a special message C: C: enjoy, andrew C: -----BEGIN PGP SIGNATURE----- C: Version: fakePGP v0.0 C: C: aefiuh98ar7ehfpo34h9q83h4fp9q34h9a8efha9348hao C: 98h5nbq3rub9a08ahfoi4no34= C: -----END PGP SIGNATURE----- C: C: -----BEGIN PGP SIGNED MESSAGE----- C: Hash: SHA1 C: C: ps. this is a secret that Doug doesn't know C: -----BEGIN PGP SIGNATURE----- C: Version: fakePGP v0.0 C: C: 98sdu9bd9fu4eiob3iovb9eb93buiou908fhv9sf C: jlknsdfi0h93un= C: -----END PGP SIGNATURE----- C: . S: 250 okay C: QUIT S: 250 bye bye 5.1.2 Component Message Signing This method creates a single signature for each distinct message contained in a set of messages encoded using the SLIDE extension. During encoding of the SLIDE message, each component message that needs to be signed can have a signature generated for it before the component messages are SLIDE Ward [Page 8] INTERNET-DRAFT SMTP Service Extension SLIDE 15 June 2000 encoded. It is important to note that in most (if not all) cases this will not work for encryption, as the same text in the unencrypted component messages will not generate the same encrypted group of octets. As an example, consider the component message approach as applied to the first usage example presented in section 4. S: C: S: 220 anstruther.elsewhere.com SMTP ready C: EHLO burleigh.uwaterloo.ca S: 250-hello burleigh.uwaterloo.ca S: 250 SLIDE C: MAIL FROM: S: 250 ... sender okay C: RCPT TO: SLIDERANGE=0-148,180-322,484-677 S: 250 ... recipient and SLIDERANGE okay C: RCPT TO: SLIDERANGE=0-121,149-483,675-677 S: 250 ... recipient and SLIDERANGE okay C: DATA S: 354 octets beyond 678 will not be relayed, end with CRLF.CRLF C: Message-ID: <1234.abcd@uwaterloo.ca> C: Date: Mon, 03 Apr 2000 12:05:10 -0400 C: From: Andrew C: To: Ed C: To: Doug C: Subject: special message C: C: -----BEGIN PGP SIGNED MESSAGE----- C: Hash: SHA1 C: C: this is the message body for a special message C: C: enjoy, andrew C: -----BEGIN PGP SIGNATURE----- C: Version: fakePGP v0.0 C: C: nsdf9n934nioq3j4un9ua9fvuerh98h43n9ae8u85 C: 34kjfbna9ea9e8rb8d9sd0ge3= C: -----END PGP SIGNATURE----- C: C: ps. this is a secret that Doug doesn't know C: -----BEGIN PGP SIGNATURE----- C: Version: fakePGP v0.0 C: Ward [Page 9] INTERNET-DRAFT SMTP Service Extension SLIDE 15 June 2000 C: ikbdfv98u4bka8rhi34ubkq3828756bkjai7rf7 C: 1kj3k4jnkj3kjk3= C: -----END PGP SIGNATURE----- C: . S: 250 okay C: QUIT S: 250 bye bye 6. Acknowledgements Thanks to Ed, Doug, Laurene and Rachael for their (unwilling) participation in the usage examples. Thanks to Dan Wing for his suggested improvements in usage examples and security considerations. 7. References [Bradner 1997] Bradner, S. "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119. March 1997. [Crocker 1982] Crocker, D. "Standard for the Format of ARPA Internet Text Messages", STD 11, RFC 822. UDEL, August 1982. [Klensin, et al 1995] Klensin, J., N. Freed, M. Rose, E. Stefferud, and D. Crocker. "SMTP Service Extensions", STD 10, RFC 1869. November 1995. [Postel 1982] Postel, J. "Simple Mail Transfer Protocol", STD 10, RFC 821. USC/Information Sciences Institute, August 1982. 8. Author's Address Andrew Ward 70 Gruhn Street Kitchener, ON N2G 1S6 CANADA Phone: +1 519 581 1201 EMail: amward@uwaterloo.ca EXPIRES: 15 December 2000 Ward [Page 10]