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.
Abstract
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.
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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:
<type-specifier>:<arg1>[:<arg2>[:...]]
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>
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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"
is:
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
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