Network Working Group                                       Mike StJohns
Request for Comments: 931                                           TPSC
Supersedes: RFC 912                                         January 1985

                         Authentication Server

STATUS OF THIS MEMO

   This RFC suggests a proposed protocol for the ARPA-Internet
   community, and requests discussion and suggestions for improvements.
   This is the second draft of this proposal (superseding RFC 912) and
   incorporates a more formal description of the syntax for the request
   and response dialog, as well as a change to specify the type of user
   identification returned.  Distribution of this memo is unlimited.

INTRODUCTION

   The Authentication Server Protocol provides a means to determine the
   identity of a user of a particular TCP connection.  Given a TCP port
   number pair, it returns a character string which identifies the owner
   of that connection on the server's system.  Suggested uses include
   automatic identification and verification of a user during an FTP
   session, additional verification of a TAC dial up user, and access
   verification for a generalized network file server.

OVERVIEW

   This is a connection based application on TCP.  A server listens for
   TCP connections on TCP port 113 (decimal).  Once a connection is
   established, the server reads one line of data which specifies the
   connection of interest.  If it exists, the system dependent user
   identifier of the connection of interest is sent out the connection.
   The service closes the connection after sending the user identifier.

RESTRICTIONS

   Queries are permitted only for fully specified connections. The
   local/foreign host pair used to fully specify the connection are
   taken from the query connection.  This means a user on Host A may
   only query the server on Host B about connections between A and B.

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QUERY/RESPONSE FORMAT

   The server accepts simple text query requests of the form

      <local-port>, <foreign-port>

   where <local-port> is the TCP port (decimal) on the target (server)
   system, and <foreign-port> is the TCP port (decimal) on the source
   (user) system.

      For example:

         23, 6191

   The response is of the form

      <local-port>, <foreign-port> : <response-type> : <additional-info>

   where <local-port>,<foreign-port> are the same pair as the query,
   <response-type> is a keyword identifying the type of response, and
   <additional info> is context dependent.

      For example:

         23, 6191 : USERID : MULTICS : StJohns.DODCSC.a
         23, 6193 : USERID : TAC : MCSJ-MITMUL
         23, 6195 : ERROR : NO-USER

RESPONSE TYPES

   A response can be one of two types:

   USERID

      In this case, <additional-info> is a string consisting of an
      operating system name, followed by a ":", followed by user
      identification string in a format peculiar to the operating system
      indicated.  Permitted operating system names are specified in
      RFC-923, "Assigned Numbers" or its successors.  The only other
      names permitted are "TAC" to specify a BBN Terminal Access
      Controller, and "OTHER" to specify any other operating system not
      yet registered with the NIC.

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   ERROR

      For some reason the owner of <TCP-port> could not be determined,
      <additional-info> tells why.  The following are suggested values
      of <additional-info> and their meanings.

      INVALID-PORT

         Either the local or foreign port was improperly specified.

      NO-USER

         The connection specified by the port pair is not currently in
         use.

      UNKNOWN-ERROR

         Can't determine connection owner; reason unknown.  Other values
         may be specified as necessary.

CAVEATS

   Unfortunately, the trustworthiness of the various host systems that
   might implement an authentication server will vary quite a bit.  It
   is up to the various applications that will use the server to
   determine the amount of trust they will place in the returned
   information.  It may be appropriate in some cases restrict the use of
   the server to within a locally controlled subnet.

APPLICATIONS

   1) Automatic user authentication for FTP

      A user-FTP may send a USER command with no argument to the
      server-FTP to request automatic authentication.  The server-FTP
      will reply with a 230 (user logged in) if it can use the
      authentication.  It will reply with a 530 (not logged in) if it
      cannot authenticate the user.  It will reply with a 500 or 501
      (syntax or parameter problem) if it does not implement automatic
      authentication.  Please note that no change is needed to currently
      implemented servers to handle the request for authentication; they
      will reject it normally as a parameter problem.  This is a
      suggested implementation for experimental use only.

   2) Verification for privileged network operations.  For example,
   having the server start or stop special purpose servers.

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   3) Elimination of "double login" for TAC and other TELNET users.

      This will be implemented as a TELNET option.

FORMAL SYNTAX

   <request>     ::= <port-pair> <CR> <LF>

   <port-pair>   ::= <integer-number> "," <integer-number>

   <reply>       ::= <reply-text> <CR> <LF>

   <reply-text>  ::= <error-reply> | <auth-reply>

   <error-reply> ::= <port-pair> ":" ERROR ":" <error-type>

   <auth-reply>  ::= <port-pair> ":" USERID ":" <opsys> ":" <user-id>

   <error-type>  ::= INVALID-PORT | NO-USER | UNKNOWN-ERROR

   <opsys>       ::= TAC | OTHER | MULTICS | UNIX ...etc.
                     (See "Assigned Numbers")

   Notes on Syntax:

      1)  White space (blanks and tab characters) between tokens is not
      important and may be ignored.

      2)  White space, the token separator character (":"), and the port
      pair separator character (",") must be quoted if used within a
      token.  The quote character is a back-slash, ASCII 92 (decimal)
      ("\").  For example, a quoted colon is "\:".  The back-slash must
      also be quoted if its needed to represent itself ("\\").

Notes on User Identification Format:

   The user identifier returned by the server should be the standard one
   for the system.  For example, the standard Multics identifier
   consists of a PERSONID followed by a ".", followed by a PROJECTID,
   followed by a ".", followed by an INSTANCE TAG of one character.  An
   instance tag of "a" identifies an interactive user, and instance tag
   of "m" identifies an absentee job (batch job) user, and an instance
   tag of "z" identifies a daemon (background) user.

   Each set of operating system users must come to a consensus as to

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   what the OFFICIAL user identification for their systems will be.
   Until they register this information, they must use the "OTHER" tag
   to specify their user identification.

Notes on User Identification Translation:

   Once you have a user identifier from a remote system, you must then
   have a way of translating it into an identifier that meaningful on
   the local system.  The following is a sketchy outline of table driven
   scheme for doing this.

   The table consists of four columns, the first three are used to match
   against, the fourth is the result.

      USERID              Opsys     Address     Result
      MCSJ-MITMUL         TAC       26.*.*.*    StJohns
      *                   MULTICS   192.5.42.*  =
      *                   OTHER     10.0.0.42   anonymous
      MSJ                 ITS       10.3.0.44   StJohns

   The above table is a sample one for a Multics system on MILNET at the
   Pentagon.  When an authentication is returned, the particular
   application using the userid simply looks for the first match in the
   table.  Notice the second line.  It says that any authentication
   coming from a Multics system on Net 192.5.42 is accepted in the same
   format.

   Obviously, various users will have to be registered to use this
   facility, but the registration can be done at the same time the use
   receives his login identity from the system.