TELNET Authentication Using DSA
RFC 2943

Document Type RFC - Proposed Standard (September 2000; No errata)
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Network Working Group                                         R. Housley
Request for Comments: 2943                                    T. Horting
Category: Standards Track                                         P. Yee
                                                                  SPYRUS
                                                          September 2000

                    TELNET Authentication Using DSA

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 (2000).  All Rights Reserved.

Abstract

   This document defines a telnet authentication mechanism using the
   Digital Signature Algorithm (DSA) [FIPS186].  It relies on the Telnet
   Authentication Option [RFC2941].

1. Command Names and Codes

    AUTHENTICATION           37

      Authentication Commands:

        IS                       0
        SEND                     1
        REPLY                    2
        NAME                     3

      Authentication Types:

        DSS                     14

      Modifiers:

        AUTH_WHO_MASK            1
        AUTH_CLIENT_TO_SERVER    0
        AUTH_SERVER_TO CLIENT    1

Housley, et al.             Standards Track                     [Page 1]
RFC 2943            TELNET Authentication Using DSA       September 2000

        AUTH_HOW_MASK            2
        AUTH_HOW_ONE_WAY         0
        AUTH_HOW_MUTUAL          2

        ENCRYPT_MASK            20
        ENCRYPT_OFF              0
        ENCRYPT_USING_TELOPT     4
        ENCRYPT_AFTER_EXCHANGE  16
        ENCRYPT_RESERVED        20

        INI_CRED_FWD_MASK        8
        INI_CRED_FWD_OFF         0
        INI_CRED_FWD_ON          8

      Sub-option Commands:

        DSS_INITIALIZE           1
        DSS_TOKENBA              2
        DSS_CERTA_TOKENAB        3
        DSS_CERTB_TOKENBA2       4

2. TELNET Security Extensions

   TELNET, as a protocol, has no concept of security.  Without
   negotiated options, it merely passes characters back and forth
   between the NVTs represented by the two TELNET processes.  In its
   most common usage as a protocol for remote terminal access (TCP port
   23), TELNET connects to a server that requires user-level
   authentication through a user name and password in the clear; the
   server does not authenticate itself to the user.

   The TELNET Authentication Option provides for user authentication and
   server authentication.  User authentication replaces or augments the
   normal host password mechanism.  Server authentication is normally
   done in conjunction with user authentication.

   In order to support these security services, the two TELNET entities
   must first negotiate their willingness to support the TELNET
   Authentication Option.  Upon agreeing to support this option, the
   parties are then able to perform sub-option negotiations to the
   authentication protocol to be used, and possibly the remote user name
   to be used for authorization checking.

   Authentication and parameter negotiation occur within an unbounded
   series of exchanges.  The server proposes a preference-ordered list
   of authentication types (mechanisms) which it supports.  In addition
   to listing the mechanisms it supports, the server qualifies each
   mechanism with a modifier that specifies whether the authentication

Housley, et al.             Standards Track                     [Page 2]
RFC 2943            TELNET Authentication Using DSA       September 2000

   is to be one-way or mutual, and in which direction the authentication
   is to be performed.  The client selects one mechanism from the list
   and responds to the server indicating its choice and the first set of
   authentication data needed for the selected authentication type.  The
   server and the client then proceed through whatever number of
   iterations are required to arrive at the requested authentication.

3. Use of Digital Signature Algorithm (DSA)

   DSA is also known as the Digital Signature Standard (DSS), and the
   names are used interchangeably.  This paper specifies a method in
   which DSA may be used to achieve certain security services when used
   in conjunction with the TELNET Authentication Option.  SHA-1
   [FIPS180-1] is used with DSA [FIPS186].

   DSA may provide either unilateral or mutual authentication.  Due to
   TELNET's character-by-character nature, it is not well-suited to the
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