The One-Time-Password SASL Mechanism
RFC 2444
| Document | Type |
RFC - Proposed Standard
(October 1998; No errata)
Updates RFC 2222
Was draft-ietf-otp-sasl (otp WG)
|
|
|---|---|---|---|
| Last updated | 2013-03-02 | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 2444 (Proposed Standard) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Steven Bellovin | ||
| Send notices to | (None) | ||
Network Working Group C. Newman
Request for Comments: 2444 Innosoft
Updates: 2222 October 1998
Category: Standards Track
The One-Time-Password SASL Mechanism
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 (1998). All Rights Reserved.
Abstract
OTP [OTP] provides a useful authentication mechanism for situations
where there is limited client or server trust. Currently, OTP is
added to protocols in an ad-hoc fashion with heuristic parsing. This
specification defines an OTP SASL [SASL] mechanism so it can be
easily and formally integrated into many application protocols.
1. How to Read This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED" and "MAY" in this document are to be interpreted as
defined in "Key words for use in RFCs to Indicate Requirement Levels"
[KEYWORDS].
This memo assumes the reader is familiar with OTP [OTP], OTP extended
responses [OTP-EXT] and SASL [SASL].
2. Intended Use
The OTP SASL mechanism replaces the SKEY SASL mechanism [SASL]. OTP
is a good choice for usage scenarios where the client is untrusted
(e.g., a kiosk client), as a one-time password will only give the
client a single opportunity to act on behalf of the user. OTP is
also a good choice for situations where interactive logins are
permitted to the server, as a compromised OTP authentication database
is only subject to dictionary attacks, unlike authentication
databases for other simple mechanisms such as CRAM-MD5 [CRAM-MD5].
Newman Standards Track [Page 1]
RFC 2444 OTP SASL Mechanism October 1998
It is important to note that each use of the OTP mechanism causes the
authentication database entry for a user to be updated.
This SASL mechanism provides a formal way to integrate OTP into
SASL-enabled protocols including IMAP [IMAP4], ACAP [ACAP], POP3
[POP-AUTH] and LDAPv3 [LDAPv3].
3. Profiling OTP for SASL
OTP [OTP] and OTP extended responses [OTP-EXT] offer a number of
options. However, for authentication to succeed, the client and
server need compatible option sets. This specification defines a
single SASL mechanism: OTP. The following rules apply to this
mechanism:
o The extended response syntax MUST be used.
o Servers MUST support the following four OTP extended responses:
"hex", "word", "init-hex" and "init-word". Servers MUST support
the "word" and "init-word" responses for the standard dictionary
and SHOULD support alternate dictionaries. Servers MUST NOT
require use of any additional OTP extensions or options.
o Clients SHOULD support display of the OTP challenge to the user
and entry of an OTP in multi-word format. Clients MAY also
support direct entry of the pass phrase and compute the "hex" or
"word" response.
o Clients MUST indicate when authentication fails due to the
sequence number getting too low and SHOULD offer the user the
option to reset the sequence using the "init-hex" or "init-word"
response.
Support for the MD5 algorithm is REQUIRED, and support for the SHA1
algorithm is RECOMMENDED.
4. OTP Authentication Mechanism
The mechanism does not provide any security layer.
The client begins by sending a message to the server containing the
following two pieces of information.
(1) An authorization identity. When the empty string is used, this
defaults to the authentication identity. This is used by system
administrators or proxy servers to login with a different user
identity. This field may be up to 255 octets and is terminated by a
NUL (0) octet. US-ASCII printable characters are preferred, although
Newman Standards Track [Page 2]
RFC 2444 OTP SASL Mechanism October 1998
UTF-8 [UTF-8] printable characters are permitted to support
international names. Use of character sets other than US-ASCII and
UTF-8 is forbidden.
(2) An authentication identity. The identity whose pass phrase will
be used. This field may be up to 255 octets. US-ASCII printable
characters are preferred, although UTF-8 [UTF-8] printable characters
are permitted to support international names. Use of character sets
other than US-ASCII and UTF-8 is forbidden.
The server responds by sending a message containing the OTP challenge
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