The One-Time-Password SASL Mechanism (RFC2444)
Original Publication Date: 1998-Oct-01
Included in the Prior Art Database: 2019-Feb-11
Internet Society Requests For Comment (RFCs)
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 mechanism so it can be easily and formally integrated into many application protocols. [STANDARDS-TRACK]
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 (C) The Internet Society (1998). All Rights Reserved.
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 pa...