OTP Extended Responses
RFC 2243

Document Type RFC - Proposed Standard (November 1997; No errata)
Last updated 2013-03-02
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Network Working Group                                           C. Metz
Request for Comments: 2243                                The Inner Net
Category: Standards Track                                 November 1997

                         OTP Extended Responses

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 (1997).  All Rights Reserved.


   This document provides a specification for a type of response to an
   OTP [RFC 1938] challenge that carries explicit indication of the
   response's encoding. Codings for the two mandatory OTP data formats
   using this new type of response are presented.

   This document also provides a specification for a response that
   allows an OTP generator to request that a server re-initialize a
   sequence and change parameters such as the secret pass phrase.

1. Conventions, Terms, and Notation

   This document specifies the data formats and software behaviors
   needed to use OTP extended responses. The data formats are described
   three ways: using an ad-hoc UNIX manual page style syntax, using
   augmented BNF described in sections two and three of RFC 822, and by
   examples. Should there be any conflict between these descriptions,
   the augmented BNF takes precedence. The software behaviors are
   described in words, and specific behavior compliance requirements are
   itemized using the requirements terminology (specifically, the words
   MUST, SHOULD, and MAY) defined in RFC 2119.

Metz                        Standards Track                     [Page 1]
RFC 2243                 OTP Extended Responses            November 1997

2. Extended Challenges and Extended Responses

   This document builds on the protocol and terminology specified in RFC
   1938 and assumes that you have already read this document and
   understand its contents.

   An extended challenge is a single line of printable text terminated
   by either a new line sequence appropriate for the context of its use
   (e.g., ASCII CR followed by ASCII LF) or a whitespace character. It
   contains a standard OTP challenge, a whitespace character, and a list
   that generators use to determine which extended responses are
   supported by a server.

   An extended response is a single line of printable text terminated by
   a new line sequence appropriate for the context of its use. It
   contains two or more tokens that are separated with a single colon
   (':') character. The first token contains a type specifier that
   indicates the format of the rest of the response. The tokens that
   follow are argument data for the OTP extended response. At least one
   token of data MUST be present.

2.1. Syntax

   In UNIX manual page like syntax, the general form of an extended
   challenge could be described as:

      <standard OTP challenge> ext[,<extension set id>[, ...]]

   And the general form of an extended response could be described as:


   In augmented BNF syntax, the syntax of the general form of an
   extended challenge and an extended response is:

   extended-challenge = otp-challenge 1*LWSP-char capability-list
                        (NL / *LWSP-char)
   otp-challenge     = <a standard OTP challenge>
   capability-list   = "ext" *("," extension-set-id)
   extension-set-id  = *<any CHAR except LWSP, CTLs, or ",">
   extended-response = type 1*(":" argument) NL
   type              = token
   argument          = token
   token             = 1*<any CHAR except ":" and CTLs>
   NL                = <new line sequence appropriate for the context
                        in which OTP is being used>

Metz                        Standards Track                     [Page 2]
RFC 2243                 OTP Extended Responses            November 1997

   An example of an extended challenge indicating support for OTP
   extended responses and for a mythical response set "foo" is:

      otp-md5 123 mi1234 ext,foo

   An example of an extended response using a mythical type named "foo"

      foo:some data:some more data:12345

2.2. Requirements

   A server compliant with this specification:

      1. MUST be able to receive and parse the general form of an
         extended response
      2. MUST be able to receive, parse, and correctly process all
         extended responses specified in this document
      3. MUST process the type field in a case-insensitive manner
      4. MUST reject any authentication attempt using an extended
         response if it does not support that type of response
      5. SHOULD provide an appropriate indication to the generator
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