The SecurID(r) SASL Mechanism
RFC 2808

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Network Working Group                                        M. Nystrom
Request for Comments: 2808                             RSA Laboratories
Category: Informational                                      April 2000

                     The SecurID(r) SASL Mechanism

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   SecurID is a hardware token card product (or software emulation
   thereof) produced by RSA Security Inc., which is used for end-user
   authentication. This document defines a SASL [RFC2222] authentication
   mechanism using these tokens, thereby providing a means for such
   tokens to be used in SASL environments. This mechanism is only for
   authentication, and has no effect on the protocol encoding and is not
   designed to provide integrity or confidentiality services.

   This memo assumes the reader has basic familiarity with the SecurID
   token, its associated authentication protocol and SASL.

How to read this document

   The key words "MUST", "MUST NOT", "SHALL", "SHOULD" and "MAY" in this
   document are to be interpreted as defined in [RFC2119].

   In examples, "C:" and "S:" indicate messages sent by the client and
   server respectively.

1. Introduction

   The SECURID SASL mechanism is a good choice for usage scenarios where
   a client, acting on behalf of a user, is untrusted, as a one-time
   passcode will only give the client a single opportunity to act
   maliciously. This mechanism provides authentication only.

Nystrom                      Informational                      [Page 1]
RFC 2808             The SecurID(r) SASL Mechanism            April 2000

   The SECURID SASL mechanism provides a formal way to integrate the
   existing SecurID authentication method into SASL-enabled protocols
   including IMAP [RFC2060], ACAP [RFC2244], POP3 [RFC1734] and LDAPv3
   [RFC2251].

2. Authentication Model

   The SECURID SASL mechanism provides two-factor based user
   authentication as defined below.

   There are basically three entities in the authentication mechanism
   described here: A user, possessing a SecurID token, an application
   server, to which the user wants to connect, and an authentication
   server, capable of authenticating the user. Even though the
   application server in practice may function as a client with respect
   to the authentication server, relaying authentication credentials
   etc. as needed, both servers are, unless explicitly mentioned,
   collectively termed "the server" here. The protocol used between the
   application server and the authentication server is outside the scope
   of this memo. The application client, acting on behalf of the user,
   is termed "the client".

   The mechanism is based on the use of a shared secret key, or "seed",
   and a personal identification number (PIN), which is known both by
   the user and the authentication server. The secret seed is stored on
   a token that the user possesses, as well as on the authentication
   server. Hence the term "two-factor authentication", a user needs not
   only physical access to the token but also knowledge about the PIN in
   order to perform an authentication. Given the seed, current time of
   day, and the PIN, a "PASSCODE(r)" is generated by the user's token
   and sent to the server.

   The SECURID SASL mechanism provides one service:

   -    User authentication where the user provides information to the
        server, so that the server can authenticate the user.

   This mechanism is identified with the SASL key "SECURID".

3. Authentication Procedure

   a) The client generates the credentials using local information
      (seed, current time and user PIN/password).

Nystrom                      Informational                      [Page 2]
RFC 2808             The SecurID(r) SASL Mechanism            April 2000

   b) If the underlying protocol permits, the client sends credentials
      to the server in an initial response message. Otherwise, the
      client sends a request to the server to initiate the
      authentication mechanism, and sends credentials after the server's
      response (see [RFC2222] section 5.1 for more information regarding
      the initial response option).

      Unless the server requests a new PIN (see below), the contents of
      the client's initial response SHALL be as follows:

      (1) An authorization identity. When this field is empty, it
      defaults to the authentication identity.  This field MAY be used
      by system administrators or proxy servers to login with a
      different user identity. This field MUST NOT be longer than 255
      octets, SHALL be terminated by a NUL (0) octet, and MUST consist
      of UTF-8-encoded [RFC2279] printable characters only (US-ASCII