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Network Working Group                                       Mike StJohnsRequest for Comments: 931                                           TPSCSupersedes:RFC 912                                         January 1985Authentication ServerSTATUS 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 (supersedingRFC 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.StJohns                                                         [Page 1]

RFC 931                                                     January 1985Authentication ServerQUERY/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-USERRESPONSE 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 inRFC-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.StJohns                                                         [Page 2]

RFC 931                                                     January 1985Authentication Server   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.StJohns                                                         [Page 3]

RFC 931                                                     January 1985Authentication Server   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 toStJohns                                                         [Page 4]

RFC 931                                                     January 1985Authentication Server   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.StJohns                                                         [Page 5]