Telnet Authentication Option
RFC 1409

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Network Working Group                                  D. Borman, Editor
Request for Comments: 1409                           Cray Research, Inc.
                                                            January 1993

                      Telnet Authentication Option

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  Discussion and suggestions for improvement are requested.
   Please refer to the current edition of the "IAB Official Protocol
   Standards" for the standardization state and status of this protocol.
   Distribution of this memo is unlimited.

1.  Command Names and Codes

   AUTHENTICATION  37
       IS               0
       SEND             1
       REPLY            2
       NAME             3

       Authentication Types
       NULL             0
       KERBEROS_V4      1
       KERBEROS_V5      2
       SPX              3
       RSA              6
       LOKI            10

       Modifiers
       AUTH_WHO_MASK        1
       AUTH_CLIENT_TO_SERVER    0
       AUTH_SERVER_TO_CLIENT    1
       AUTH_HOW_MASK        2
       AUTH_HOW_ONE_WAY         0
       AUTH_HOW_MUTUAL          2

2.  Command Meanings

   This document makes reference to a "server" and a "client".  For the
   purposes of this document, the "server" is the side of the connection
   that did the passive TCP open (TCP LISTEN state), and the "client" is
   the side of the connection that did the active open.

Telnet Working Group                                            [Page 1]
RFC 1409              Telnet Authentication Option          January 1993

   IAC WILL AUTHENTICATION

      The client side of the connection sends this command to indicate
      that it is willing to send and receive authentication information.

   IAC DO AUTHENTICATION

      The servers side of the connection sends this command to indicate
      that it is willing to send and receive authentication information.

   IAC WONT AUTHENTICATION

      The client side of the connection sends this command to indicate
      that it refuses to send or receive authentication information; the
      server side sends this command if it receives a DO AUTHENTICATION
      command.

   IAC DONT AUTHENTICATION

      The server side of the connection sends this command to indicate
      that it refuses to send or receive authentication information; the
      client side sends this command if it receives a WILL
      AUTHENTICATION command.

   IAC SB AUTHENTICATION SEND authentication-type-pair-list IAC SE

      The sender of this command (the server) requests that the remote
      side send authentication information for one of the authentication
      types listed in "authentication-type-pair-list".  The
      "authentication-type-pair-list" is an ordered list of
      "authentication-type" pairs.  Only the server side (DO
      AUTHENTICATION) is allowed to send this.

   IAC SB AUTHENTICATION IS authentication-type-pair <auth data> IAC SE

      The sender of this command (the client) is sending the
      authentication information for authentication type
      "authentication-type-pair".  Only the client side (WILL
      AUTHENTICATION) is allowed to send this.

   IAC SB AUTHENTICATION REPLY authentication-type-pair <auth data> IAC
   SE

      The sender of this command (the server) is sending a reply to the
      the authentication information received in a previous IS command.
      Only the server side (DO AUTHENTICATION) is allowed to send this.

Telnet Working Group                                            [Page 2]
RFC 1409              Telnet Authentication Option          January 1993

   IAC SB AUTHENTICATION NAME remote-user IAC SE

      This optional command is sent to specify the account name on the
      remote host that the user wishes to be authorized to use.  Note
      that authentication may succeed, and the authorization to use a
      particular account may still fail.  Some authentication mechanisms
      may ignore this command.

   The "authentication-type-pair" is two octets, the first is the
   authentication type (as listed in Section 1, additions to this list
   must be registered with the Internet Assigned Numbers Authority
   (IANA)), and the second is a modifier to the type.  There are
   currently two one bit fields defined in the modifier, the
   AUTH_WHO_MASK bit and the AUTH_HOW_MASK bit, so there are four
   possible combinations:

      AUTH_CLIENT_TO_SERVER
      AUTH_HOW_ONE_WAY

         The client will send authentication information about the local
         user to the server.  If the negotiation is successful, the
         server will have authenticated the user on the client side of
         the connection.

      AUTH_SERVER_TO_CLIENT
      AUTH_HOW_ONE_WAY

         The server will authenticate itself to the client.  If the
         negotiation is successful, the client will know that it is
         connected to the server that it wants to be connected to.