One document matched: draft-myers-smtp-auth-04.txt

Differences from draft-myers-smtp-auth-03.txt

Network Working Group                                           J. Myers
Internet Draft: SMTP Authentication                      Carnegie Mellon
Document: draft-myers-smtp-auth-04.txt                     November 1996


                         SMTP Service Extension
                           for Authentication
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
   working documents as Internet Drafts.

   Internet Drafts are draft documents valid for a maximum of six
   months.  Internet Drafts may be updated, replaced, or obsoleted by
   other documents at any time.  It is not appropriate to use Internet
   Drafts as reference material or to cite them other than as a
   ``working draft'' or ``work in progress``.

   To learn the current status of any Internet-Draft, please check the
   1id-abstracts.txt listing contained in the Internet-Drafts Shadow
   Directories on ds.internic.net, nic.nordu.net, ftp.isi.edu, or
   munnari.oz.au.

   A revised version of this draft document will be submitted to the RFC
   editor as a Proposed Standard for the Internet Community.  Discussion
   and suggestions for improvement are requested.  This document will
   expire before July 1996.  Distribution of this draft is unlimited.


1. Introduction

   This document defines an extension to the SMTP service 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].











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2. 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"

   (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) No additional parameters are added to either the MAIL FROM or
       RCPT TO commands.


3. 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.

     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



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         must reject the AUTH command by sending a 501 reply.

         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.
         If the initial-response argument to the AUTH command is used
         with a mechanism that sends data in the initial challenge, the
         server should reject 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.  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.

         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.  In other words, the client may
         request authentication types in decreasing order of preference.

         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.











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     Examples:
         S: 220 smtp.andrew.cmu.edu ESMTP server ready
         C: EHLO jgm.pc.cc.cmu.edu
         S: 250-smtp.andrew.cmu.edu
         S: 250 AUTH=SKEY
         C: AUTH FOOBAR
         S: 504 Unrecognized authentication type
         C: AUTH SKEY c21pdGg=
         S: 334 OTUgUWE1ODMwOA==
         C: BsAY3g4gBNo=
         S: 235 S/Key authentication successful








































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4. Formal Syntax

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) notation as specified in [RFC822].

   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.

   ATOM_CHAR       ::= <any CHAR except atom_specials>

   atom_specials   ::= "(" / ")" / "{" / SPACE / CTLs / "%" / "*" /
                       <"> / "\"

   auth_command    ::= "AUTH" SPACE auth_type [SPACE base64]
                           *(CRLF base64) CRLF

   auth_type       ::= 1*ATOM_CHAR

   base64          ::= *(4base64_CHAR) [base64_terminal]

   base64_char     ::= "A" / "B" / "C" / "D" / "E" / "F" / "G" / "H" /
                       "I" / "J" / "K" / "L" / "M" / "N" / "O" / "P" /
                       "Q" / "R" / "S" / "T" / "U" / "V" / "W" / "X" /
                       "Y" / "Z" /
                       "a" / "b" / "c" / "d" / "e" / "f" / "g" / "h" /
                       "i" / "j" / "k" / "l" / "m" / "n" / "o" / "p" /
                       "q" / "r" / "s" / "t" / "u" / "v" / "w" / "x" /
                       "y" / "z" /
                       "0" / "1" / "2" / "3" / "4" / "5" / "6" / "7" /
                       "8" / "9" / "+" / "/"
                       ;; Case-sensitive

   base64_terminal ::= (2base64_char "==") / (3base64_char "=")

   CHAR            ::= <any 7-bit US-ASCII character except NUL,
                        0x01 - 0x7f>

   continue_req    ::= "334" SPACE base64 CRLF

   CR              ::= <ASCII CR, carriage return, 0x0C>

   CRLF            ::= CR LF

   CTL             ::= <any ASCII control character and DEL,
                        0x00 - 0x1f, 0x7f>




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   LF              ::= <ASCII LF, line feed, 0x0A>

   SPACE           ::= <ASCII SP, space, 0x20>



5. References

   [SASL]  Myers, J., "Simple Authentication and Security Layer",
   draft-myers-auth-sasl-XX.txt, Carnegie Mellon.

   [RFC821] Postel, J., "Simple Mail Transfer Protocol", RFC 821, August
   1982.

   [RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text
   Messages", RFC 822, August 1982.



6. 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.

   This extension does not provide a defined mechanism for
   authentication using a plaintext password.  This omission is
   intentional.

   This extension is not intended to replace or be used instead of end-
   to-end message signature and encryption systems such as PEM 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




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      (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.

          Additional security considerations are mentioned in the SASL
          specification [SASL].



7. Author's Address:

   John G. Myers
   Carnegie-Mellon University
   5000 Forbes Ave
   Pittsburgh, PA 15213

   EMail: jgm+@cmu.edu

































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