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diff --git a/RFC/rfc2554.txt b/RFC/rfc2554.txt deleted file mode 100644 index 2922deae..00000000 --- a/RFC/rfc2554.txt +++ /dev/null @@ -1,619 +0,0 @@ - - - - - - -Network Working Group J. Myers -Request for Comments: 2554 Netscape Communications -Category: Standards Track March 1999 - - - SMTP Service Extension - for Authentication - -Status of this Memo - - This document specifies an Internet standards track protocol for the - Internet community, and requests discussion and suggestions for - improvements. Please refer to the current edition of the "Internet - Official Protocol Standards" (STD 1) for the standardization state - and status of this protocol. Distribution of this memo is unlimited. - -Copyright Notice - - Copyright (C) The Internet Society (1999). All Rights Reserved. - - -1. Introduction - - This document defines an SMTP service extension [ESMTP] whereby an - SMTP client may indicate an authentication mechanism to the server, - perform an authentication protocol exchange, and optionally negotiate - a security layer for subsequent protocol interactions. This - extension is a profile of the Simple Authentication and Security - Layer [SASL]. - - -2. Conventions Used in this Document - - In examples, "C:" and "S:" indicate lines sent by the client and - server respectively. - - The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" - in this document are to be interpreted as defined in "Key words for - use in RFCs to Indicate Requirement Levels" [KEYWORDS]. - - -3. The Authentication service extension - - - (1) the name of the SMTP service extension is "Authentication" - - (2) the EHLO keyword value associated with this extension is "AUTH" - - - - -Myers Standards Track [Page 1] - -RFC 2554 SMTP Authentication March 1999 - - - (3) The AUTH EHLO keyword contains as a parameter a space separated - list of the names of supported SASL mechanisms. - - (4) a new SMTP verb "AUTH" is defined - - (5) an optional parameter using the keyword "AUTH" is added to the - MAIL FROM command, and extends the maximum line length of the - MAIL FROM command by 500 characters. - - (6) this extension is appropriate for the submission protocol - [SUBMIT]. - - -4. The AUTH command - - AUTH mechanism [initial-response] - - Arguments: - a string identifying a SASL authentication mechanism. - an optional base64-encoded response - - Restrictions: - After an AUTH command has successfully completed, no more AUTH - commands may be issued in the same session. After a successful - AUTH command completes, a server MUST reject any further AUTH - commands with a 503 reply. - - The AUTH command is not permitted during a mail transaction. - - Discussion: - The AUTH command indicates an authentication mechanism to the - server. If the server supports the requested authentication - mechanism, it performs an authentication protocol exchange to - authenticate and identify the user. Optionally, it also - negotiates a security layer for subsequent protocol - interactions. If the requested authentication mechanism is not - supported, the server rejects the AUTH command with a 504 - reply. - - The authentication protocol exchange consists of a series of - server challenges and client answers that are specific to the - authentication mechanism. A server challenge, otherwise known - as a ready response, is a 334 reply with the text part - containing a BASE64 encoded string. The client answer consists - of a line containing a BASE64 encoded string. If the client - wishes to cancel an authentication exchange, it issues a line - with a single "*". If the server receives such an answer, it - MUST reject the AUTH command by sending a 501 reply. - - - -Myers Standards Track [Page 2] - -RFC 2554 SMTP Authentication March 1999 - - - The optional initial-response argument to the AUTH command is - used to save a round trip when using authentication mechanisms - that are defined to send no data in the initial challenge. - When the initial-response argument is used with such a - mechanism, the initial empty challenge is not sent to the - client and the server uses the data in the initial-response - argument as if it were sent in response to the empty challenge. - Unlike a zero-length client answer to a 334 reply, a zero- - length initial response is sent as a single equals sign ("="). - If the client uses an initial-response argument to the AUTH - command with a mechanism that sends data in the initial - challenge, the server rejects the AUTH command with a 535 - reply. - - If the server cannot BASE64 decode the argument, it rejects the - AUTH command with a 501 reply. If the server rejects the - authentication data, it SHOULD reject the AUTH command with a - 535 reply unless a more specific error code, such as one listed - in section 6, is appropriate. Should the client successfully - complete the authentication exchange, the SMTP server issues a - 235 reply. - - The service name specified by this protocol's profile of SASL - is "smtp". - - If a security layer is negotiated through the SASL - authentication exchange, it takes effect immediately following - the CRLF that concludes the authentication exchange for the - client, and the CRLF of the success reply for the server. Upon - a security layer's taking effect, the SMTP protocol is reset to - the initial state (the state in SMTP after a server issues a - 220 service ready greeting). The server MUST discard any - knowledge obtained from the client, such as the argument to the - EHLO command, which was not obtained from the SASL negotiation - itself. The client MUST discard any knowledge obtained from - the server, such as the list of SMTP service extensions, which - was not obtained from the SASL negotiation itself (with the - exception that a client MAY compare the list of advertised SASL - mechanisms before and after authentication in order to detect - an active down-negotiation attack). The client SHOULD send an - EHLO command as the first command after a successful SASL - negotiation which results in the enabling of a security layer. - - The server is not required to support any particular - authentication mechanism, nor are authentication mechanisms - required to support any security layers. If an AUTH command - fails, the client may try another authentication mechanism by - issuing another AUTH command. - - - -Myers Standards Track [Page 3] - -RFC 2554 SMTP Authentication March 1999 - - - If an AUTH command fails, the server MUST behave the same as if - the client had not issued the AUTH command. - - The BASE64 string may in general be arbitrarily long. Clients - and servers MUST be able to support challenges and responses - that are as long as are generated by the authentication - mechanisms they support, independent of any line length - limitations the client or server may have in other parts of its - protocol implementation. - - Examples: - S: 220 smtp.example.com ESMTP server ready - C: EHLO jgm.example.com - S: 250-smtp.example.com - S: 250 AUTH CRAM-MD5 DIGEST-MD5 - C: AUTH FOOBAR - S: 504 Unrecognized authentication type. - C: AUTH CRAM-MD5 - S: 334 - PENCeUxFREJoU0NnbmhNWitOMjNGNndAZWx3b29kLmlubm9zb2Z0LmNvbT4= - C: ZnJlZCA5ZTk1YWVlMDljNDBhZjJiODRhMGMyYjNiYmFlNzg2ZQ== - S: 235 Authentication successful. - - - -5. The AUTH parameter to the MAIL FROM command - - AUTH=addr-spec - - Arguments: - An addr-spec containing the identity which submitted the message - to the delivery system, or the two character sequence "<>" - indicating such an identity is unknown or insufficiently - authenticated. To comply with the restrictions imposed on ESMTP - parameters, the addr-spec is encoded inside an xtext. The syntax - of an xtext is described in section 5 of [ESMTP-DSN]. - - Discussion: - The optional AUTH parameter to the MAIL FROM command allows - cooperating agents in a trusted environment to communicate the - authentication of individual messages. - - If the server trusts the authenticated identity of the client to - assert that the message was originally submitted by the supplied - addr-spec, then the server SHOULD supply the same addr-spec in an - AUTH parameter when relaying the message to any server which - supports the AUTH extension. - - - - -Myers Standards Track [Page 4] - -RFC 2554 SMTP Authentication March 1999 - - - A MAIL FROM parameter of AUTH=<> indicates that the original - submitter of the message is not known. The server MUST NOT treat - the message as having been originally submitted by the client. - - If the AUTH parameter to the MAIL FROM is not supplied, the - client has authenticated, and the server believes the message is - an original submission by the client, the server MAY supply the - client's identity in the addr-spec in an AUTH parameter when - relaying the message to any server which supports the AUTH - extension. - - If the server does not sufficiently trust the authenticated - identity of the client, or if the client is not authenticated, - then the server MUST behave as if the AUTH=<> parameter was - supplied. The server MAY, however, write the value of the AUTH - parameter to a log file. - - If an AUTH=<> parameter was supplied, either explicitly or due to - the requirement in the previous paragraph, then the server MUST - supply the AUTH=<> parameter when relaying the message to any - server which it has authenticated to using the AUTH extension. - - A server MAY treat expansion of a mailing list as a new - submission, setting the AUTH parameter to the mailing list - address or mailing list administration address when relaying the - message to list subscribers. - - It is conforming for an implementation to be hard-coded to treat - all clients as being insufficiently trusted. In that case, the - implementation does nothing more than parse and discard - syntactically valid AUTH parameters to the MAIL FROM command and - supply AUTH=<> parameters to any servers to which it - authenticates using the AUTH extension. - - Examples: - C: MAIL FROM:<e=mc2@example.com> AUTH=e+3Dmc2@example.com - S: 250 OK - - - - - - - - - - - - - - -Myers Standards Track [Page 5] - -RFC 2554 SMTP Authentication March 1999 - - -6. Error Codes - - The following error codes may be used to indicate various conditions - as described. - - 432 A password transition is needed - - This response to the AUTH command indicates that the user needs to - transition to the selected authentication mechanism. This typically - done by authenticating once using the PLAIN authentication mechanism. - - 534 Authentication mechanism is too weak - - This response to the AUTH command indicates that the selected - authentication mechanism is weaker than server policy permits for - that user. - - 538 Encryption required for requested authentication mechanism - - This response to the AUTH command indicates that the selected - authentication mechanism may only be used when the underlying SMTP - connection is encrypted. - - 454 Temporary authentication failure - - This response to the AUTH command indicates that the authentication - failed due to a temporary server failure. - - 530 Authentication required - - This response may be returned by any command other than AUTH, EHLO, - HELO, NOOP, RSET, or QUIT. It indicates that server policy requires - authentication in order to perform the requested action. - - - - - - - - - - - - - - - - - - -Myers Standards Track [Page 6] - -RFC 2554 SMTP Authentication March 1999 - - -7. Formal Syntax - - The following syntax specification uses the augmented Backus-Naur - Form (BNF) notation as specified in [ABNF]. - - Except as noted otherwise, all alphabetic characters are case- - insensitive. The use of upper or lower case characters to define - token strings is for editorial clarity only. Implementations MUST - accept these strings in a case-insensitive fashion. - - UPALPHA = %x41-5A ;; Uppercase: A-Z - - LOALPHA = %x61-7A ;; Lowercase: a-z - - ALPHA = UPALPHA / LOALPHA ;; case insensitive - - DIGIT = %x30-39 ;; Digits 0-9 - - HEXDIGIT = %x41-46 / DIGIT ;; hexidecimal digit (uppercase) - - hexchar = "+" HEXDIGIT HEXDIGIT - - xchar = %x21-2A / %x2C-3C / %x3E-7E - ;; US-ASCII except for "+", "=", SPACE and CTL - - xtext = *(xchar / hexchar) - - AUTH_CHAR = ALPHA / DIGIT / "-" / "_" - - auth_type = 1*20AUTH_CHAR - - auth_command = "AUTH" SPACE auth_type [SPACE (base64 / "=")] - *(CRLF [base64]) CRLF - - auth_param = "AUTH=" xtext - ;; The decoded form of the xtext MUST be either - ;; an addr-spec or the two characters "<>" - - base64 = base64_terminal / - ( 1*(4base64_CHAR) [base64_terminal] ) - - base64_char = UPALPHA / LOALPHA / DIGIT / "+" / "/" - ;; Case-sensitive - - base64_terminal = (2base64_char "==") / (3base64_char "=") - - continue_req = "334" SPACE [base64] CRLF - - - - -Myers Standards Track [Page 7] - -RFC 2554 SMTP Authentication March 1999 - - - CR = %x0C ;; ASCII CR, carriage return - - CRLF = CR LF - - CTL = %x00-1F / %x7F ;; any ASCII control character and DEL - - LF = %x0A ;; ASCII LF, line feed - - SPACE = %x20 ;; ASCII SP, space - - - - -8. References - - [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax - Specifications: ABNF", RFC 2234, November 1997. - - [CRAM-MD5] Klensin, J., Catoe, R. and P. Krumviede, "IMAP/POP - AUTHorize Extension for Simple Challenge/Response", RFC - 2195, September 1997. - - [ESMTP] Klensin, J., Freed, N., Rose, M., Stefferud, E. and D. - Crocker, "SMTP Service Extensions", RFC 1869, November - 1995. - - [ESMTP-DSN] Moore, K, "SMTP Service Extension for Delivery Status - Notifications", RFC 1891, January 1996. - - [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", BCP 14, RFC 2119, March 1997. - - [SASL] Myers, J., "Simple Authentication and Security Layer - (SASL)", RFC 2222, October 1997. - - [SUBMIT] Gellens, R. and J. Klensin, "Message Submission", RFC - 2476, December 1998. - - [RFC821] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC - 821, August 1982. - - [RFC822] Crocker, D., "Standard for the Format of ARPA Internet - Text Messages", STD 11, RFC 822, August 1982. - - - - - - - - -Myers Standards Track [Page 8] - -RFC 2554 SMTP Authentication March 1999 - - -9. Security Considerations - - Security issues are discussed throughout this memo. - - If a client uses this extension to get an encrypted tunnel through an - insecure network to a cooperating server, it needs to be configured - to never send mail to that server when the connection is not mutually - authenticated and encrypted. Otherwise, an attacker could steal the - client's mail by hijacking the SMTP connection and either pretending - the server does not support the Authentication extension or causing - all AUTH commands to fail. - - Before the SASL negotiation has begun, any protocol interactions are - performed in the clear and may be modified by an active attacker. - For this reason, clients and servers MUST discard any knowledge - obtained prior to the start of the SASL negotiation upon completion - of a SASL negotiation which results in a security layer. - - This mechanism does not protect the TCP port, so an active attacker - may redirect a relay connection attempt to the submission port - [SUBMIT]. The AUTH=<> parameter prevents such an attack from causing - an relayed message without an envelope authentication to pick up the - authentication of the relay client. - - A message submission client may require the user to authenticate - whenever a suitable SASL mechanism is advertised. Therefore, it may - not be desirable for a submission server [SUBMIT] to advertise a SASL - mechanism when use of that mechanism grants the client no benefits - over anonymous submission. - - This extension is not intended to replace or be used instead of end- - to-end message signature and encryption systems such as S/MIME or - PGP. This extension addresses a different problem than end-to-end - systems; it has the following key differences: - - (1) it is generally useful only within a trusted enclave - - (2) it protects the entire envelope of a message, not just the - message's body. - - (3) it authenticates the message submission, not authorship of the - message content - - (4) it can give the sender some assurance the message was - delivered to the next hop in the case where the sender - mutually authenticates with the next hop and negotiates an - appropriate security layer. - - - - -Myers Standards Track [Page 9] - -RFC 2554 SMTP Authentication March 1999 - - - Additional security considerations are mentioned in the SASL - specification [SASL]. - - - -10. Author's Address - - John Gardiner Myers - Netscape Communications - 501 East Middlefield Road - Mail Stop MV-029 - Mountain View, CA 94043 - - EMail: jgmyers@netscape.com - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Myers Standards Track [Page 10] - -RFC 2554 SMTP Authentication March 1999 - - -11. Full Copyright Statement - - Copyright (C) The Internet Society (1999). All Rights Reserved. - - This document and translations of it may be copied and furnished to - others, and derivative works that comment on or otherwise explain it - or assist in its implementation may be prepared, copied, published - and distributed, in whole or in part, without restriction of any - kind, provided that the above copyright notice and this paragraph are - included on all such copies and derivative works. However, this - document itself may not be modified in any way, such as by removing - the copyright notice or references to the Internet Society or other - Internet organizations, except as needed for the purpose of - developing Internet standards in which case the procedures for - copyrights defined in the Internet Standards process must be - followed, or as required to translate it into languages other than - English. - - The limited permissions granted above are perpetual and will not be - revoked by the Internet Society or its successors or assigns. - - This document and the information contained herein is provided on an - "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING - TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING - BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION - HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF - MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. - - - - - - - - - - - - - - - - - - - - - - - - -Myers Standards Track [Page 11] - |