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Versions: 00 01 02 rfc2808                                              
INTERNET-DRAFT                                                  M. Nystrom
Expires: December 1999                                         J. Brainard
Intended Category: Informational                          RSA Laboratories
<draft-nystrom-securid-sasl-01.txt>                              June 1999

                     The SecurID(r) SASL Mechanism

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of [RFC2026].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups and individuals may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft expires in December, 1999. Comments and
   suggestions on this document are encouraged. Comments on this
   document should be sent directly to the author.

Abstract

   SecurID is a hardware token card product (or software emulation
   thereof) produced by Security Dynamics, which is used for end-user
   authentication. This document defines a SASL authentication mechanism
   using these tokens, thereby providing a means for such tokens to be
   used in SASL [RFC2222] 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", "SHOULD" and "MAY" in this document are to be



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   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.

   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 one-way two-factor based
   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. Hence the term 'two-factor
   authentication'.  The secret seed is stored on a token that the
   client (user) possesses, as well as on the authentication server.
   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:

   -    Client authentication where the client provides information to
        the server, so that the server can authenticate the client.

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



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3. Authentication Procedure

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

   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 clients initial response SHALL be as follows:

      (1) An authorization identity. When this field isn't present,
      this defaults to the authentication identity.  This field may be
      used by system administrators or proxy servers to login with a
      different user identity.

      (2) An authentication identity. The identity whose passcode
      will be used. If this field isn't present, it is assumed to have
      been transferred by other means (e.g. if the underlying protocol
      has support for this, like [RFC2251]).

      (3) A passcode. The one-time password that will be used to grant
      access.

      This message is defined in ASN.1 [X680] as follows:

      SecurIDSASLCredentialsPDU ::= SEQUENCE {
          version          INTEGER {v1(0)} (v1,...) DEFAULT v1,
          authorizationID  UTF8String OPTIONAL,
          authenticationID [0] IMPLICIT UTF8String OPTIONAL,
          passcode         OCTET STRING (SIZE (4..32)),
          pin              UTF8String (SIZE (4..32)) OPTIONAL,
          ... -- For future extensions
      }

      (The 'pin' field shall only be present when the server has sent a
      request for a new user PIN.)

      Values shall be DER-encoded [X690] before transformed in
      accordance with the underlying protocol. Passcodes usually
      consist of 4-8 digits.

   c) The server verifies these credentials using its own information.
      If the verification succeeds, the server sends back a



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      response indicating success to the client. After receiving this
      response, the client is authenticated. Otherwise, the verification
      either failed or the server needs an additional set of credentials
      from the client in order to authenticate the user.

   d) If the server needs an additional set of credentials, it requests
      them now. The request has the following format and shall be
      DER-encoded before being transformed in accordance with the
      underlying protocol:

      SecurIDSASLCredentialsRequest ::= SEQUENCE {
          version INTEGER {v1(0)} (v1,...) DEFAULT v1,
          request CHOICE {
              passcode NULL,
              pin      UTF8String (SIZE (0|4..32)),
              ... -- For future extensions
          }
      }

      The 'passcode' choice will be sent when the server requests a
      passcode. The 'pin' choice will be sent when the server requests a
      new user password. The server will either send an empty string or
      suggest a new user PIN in this message.

   e) The client generates a new set of credentials using local
      information and depending on the servers request and sends them to
      the server. Authentication now continues as in c) above.

   Note 1: Case d) above may occur e.g. when the clocks on which the
   server and the client relies are not synchronized.

   Note 2: If the server requested a new user PIN, the client MUST
   respond with a new user PIN (together with a passcode), encoded as a
   UTF8String. If the server supplied the client with a suggested PIN,
   the client accepts this by replying with the same PIN, but MAY
   replace it with another one. The length of the PIN is application-
   dependent as is any other requirements for the PIN, e.g. allowed
   characters.  If the server for some reason does not accept the
   received PIN, the client MUST be prepared to receive either a message
   indicating the failure of the authentication or a repeated request
   for a new PIN. Mechanisms for transferring knowledge about PIN
   requirements from the server to the client is outside of the scope
   for this memo. However, some information MAY be provided in error
   messages transferred from the server to the client when applicable.

4. Examples

 4.1 IMAP4



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   The following example shows the use of the SECURID SASL mechanism
   with IMAP4. The example is only designed to illustrate the protocol
   interaction but does provide valid encoding examples.

   S: * OK IMAP4 server ready
   C: AOO1 CAPABILITY
   S: * CAPABILITY IMAP4 AUTH=CRAM-MD5 AUTH=SECURID
   S: A001 OK done
   C: AOO2 AUTHENTICATE SECURID
   S: +
   C: MBKABm1hZ251cwQIMTIzNDU2Nzg=
   S: AOO2 OK Welcome, SECURID authenticated user: magnus

 4.2 LDAPv3

   The following examples show the use of the SECURID SASL mechanism
   with LDAPv3. The examples are only designed to illustrate the
   protocol interaction, but does provide valid encoding examples.
   Usernames, passcodes and PINs are of course fictitious. For
   readability, all messages is shown in the value-notation defined in
   [X680].

  4.2.1 LDAPv3 Example 1

   Initial response message, successful authentication.

   C: { messageID 1,
        protocolOp bindRequest :
          { version 1,
            name '434E3D4D41474E5553'H,
            authentication sasl :
              { mechanism '53454355524944'H,
                credentials '300A04083132333435363738'H
              }
          }
      }

   S: { messageID 1,
        protocolOp bindResponse :
          { resultCode success,
            matchedDN  ''H,
            errorMessage ''H,
          }
      }

  4.2.2 LDAPv3 Example 2

   Initial response message, server requires second passcode.



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   C:  {
       messageID 1,
       protocolOp bindRequest : {
           version 1,
           name '434E3D4D41474E5553'H,
           authentication sasl : {
               mechanism '53454355524944'H,
               credentials '300A04083132333435363738'H
           }
       } }

   S:  {
       messageID 1,
       protocolOp bindResponse : {
           resultCode saslBindInProgress,
           matchedDN  ''H,
           errorMessage ''H,
           serverSaslCreds '30020500'H
       } }

   C:  {
       messageID 1,
       protocolOp bindRequest : {
           version 1,
           name '434E3D4D41474E5553'H,
           authentication sasl : {
               mechanism '53454355524944'H,
               credentials '300A04083131333335353636'H
           }
       } }

   S:  {
       messageID 1,
       protocolOp bindResponse : {
           resultCode success,
           matchedDN  ''H,
           errorMessage ''H,
       } }

  4.2.3 LDAPv3 Example 3

   Initial response message, server requires new PIN and passcode, and
   supplies client with a suggested new PIN (which the client accepts).

   C:  {
       messageID 1,
       protocolOp bindRequest : {
           version 1,



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           name '434E3D4D41474E5553'H,
           authentication sasl : {
               mechanism '53454355524944'H,
               credentials '300A04083132333435363738'H
           }
       } }

   S:  {
       messageID 1,
       protocolOp bindResponse : {
           resultCode saslBindInProgress,
           matchedDN  ''H,
           errorMessage ''H,
           serverSaslCreds '30070C056B616C6C65'H
       } }

   C:  {
       messageID 1,
       protocolOp bindRequest : {
           version 1,
           name '434E3D4D41474E5553'H,
           authentication sasl : {
               mechanism '53454355524944'H,
               credentials '3011040831323334353637380C056B616C6C65'H
           }
       } }

   S:  {
       messageID 1,
       protocolOp bindResponse : {
           resultCode success,
           matchedDN  ''H,
           errorMessage ''H,
       } }

5. Security Considerations

   This mechanism does not provide session privacy, server
   authentication or protection from active attacks. In particular,
   man-in-the-middle attacks, were an attacker acts as an application
   server in order to acquire a valid passcode are possible.

   In order to protect against such attacks,  the client SHOULD make
   sure that the server is properly authenticated. When user PINs are
   transmitted, authentication SHOULD take place on an authenticated and
   confidentiality-protected connection.

   Server implementations MUST protect against replay attacks.



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   Implementations MUST support passcodes with at least a length of 4
   characters, in order to protect against passcode-guessing attacks.

6. IANA Considerations

   By registering the SecurID protocol as a SASL mechanism, implementers
   will have a well-defined way of adding this authentication mechanism
   to their product. Here is the registration template for the SECURID
   SASL mechanism:

        SASL mechanism name:      SECURID
        Security Considerations:  See corresponding section of this memo
        Published specification:  This memo
        Person & email address to
        contact for further
        information:              See author's address section below
        Intended usage:           COMMON
        Author/Change controller: See author's address section below

7. Intellectual Property Considerations

   Neither RSA Data Security Inc. or Security Dynamics Technologies Inc.
   makes any claims on the general constructions described in this memo,
   although underlying techniques may be covered. Among the underlying
   techniques, the SecurID technology is covered by a number of US
   patents, in particular US patent no. 4,885,778, no. 5,097,505, no.
   5,168,520, and 5,657,388.

   Security Dynamics and SecurID are registered trademarks, and PASSCODE
   is a trademark, of Security Dynamics Technologies, Inc.

8. Copyright

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

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.



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   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

9. References

   [RFC1734] Myers, J., "POP3 AUTHentication command," IETF RFC 1734,
   December 1994.

   [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
   3," IETF RFC 2026, October 1996.

   [RFC2060]  Crispin, M., "Internet Message Access Protocol - Version
   4rev1," IETF RFC 2060, December 1996.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels," IETF RFC 2119, March 1997.

   [RFC2222] Myers, J., "Simple Authentication and Security Layer," IETF
   RFC 2222, October 1997.

   [RFC2244] Newman, C., "RFC2244 -- Application Configuration Access
   Protocol," IETF RFC 2244, November 1997.

   [RFC2251] Wahl, M., et al, "Lightweight Directory Access Protocol
   (v3)," IETF RFC 2252, December 1997.

   [RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO 10646,"
   IETF RFC 2279, January 1998.

   [X3.4] ANSI, "ANSI X3.4: Information Systems - Coded Character Sets -
   7-Bit American National Standard Code for Information Interchange
   (7-Bit ASCII)," American National Standards Institute.

   [X680] ITU-T, "Information technology - Abstract Syntax Notation One
   (ASN.1): Specification of basic notation," ITU-T Recommendation
   X.680, 1994.

   [X690] ITU-T, "Information technology - ASN.1 encoding rules:
   SPecification of Basic Encoding Rules (BER), Canonical Encoding Rules
   (CER) and Distinguished Encoding Rules (DER)," ITU-T Recommendation
   X.690, 1994.



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10. Acknowledgements

   The authors gratefully acknowledge the contributions of various
   reviewers of this memo, in particular the ones from John Myers.  They
   have significantly clarified and improved the utility of this
   specification.

11. Author's Address

   Magnus Nystr÷m
   RSA Laboratories
   20 Crosby Drive
   Bedford, MA 01730

   Phone: +1-781-687-7000
   Email: magnus@rsa.com

   John Brainard
   RSA Laboratories
   20 Crosby Drive
   Bedford, MA 01730

   Phone: +1-781-687-7000
   Email: jbrainard@rsa.com



























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