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Versions: 00 01 02 03 04 05 06                                          
Internet Engineering Task Force                             R. Pereira
IP Security Working Group                         TimeStep Corporation
Internet Draft
Expires in six months                                 November 6, 1998

             Extended Authentication Within ISAKMP/Oakley

Status of this Memo

   This document is a submission to the IETF Internet Protocol
   Security (IPSECond) Working Group. Comments are solicited and
   should be addressed to the working group mailing list
   (ipsec@tis.com) or to the editor.

   This document is an Internet-Draft.  Internet Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working Groups. Note that other groups may also distribute
   working documents as Internet Drafts.

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   ftp.isi.edu (US West Coast).

   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.


   This document describes a method for using existing unidirectional
   authentication mechanisms such as RADIUS, SecurID, and OTP within
   IPSec's ISAKMP protocol.

R. Pereira                                                    [Page 1]

Internet Draft                                                  Nov-98

Table of Contents

   1. Introduction...................................................2
     1.1 Extended Authentication.....................................2
     1.2 Reader Prerequisites........................................3
     1.3 Specification of Requirements...............................3
   2. Extended Authentication Method.................................3
     2.1 Simple Authentication.......................................4
     2.2 Challenge/Response..........................................4
     2.3 Two-Factor Authentication...................................5
     2.4 One-Time-Password...........................................5
   3. Extensions to ISAKMP-Config....................................5
     3.1 Message Types...............................................6
     3.2 Attributes..................................................7
     3.3 Authentication Types........................................8
   4. Other Scenarios for Extended Authentication....................9
   5. Security Considerations.......................................10
   6. References....................................................10
   7. Editor's Address..............................................11
   8. Full Copyright Statement......................................11

1. Introduction

   The following technique allows IPSec's ISAKMP/Oakley [IKE] protocol
   to support extended authentication mechanisms like two-factor
   authentication, challenge/response and other remote access
   unidirectional authentication methods.

   These authentication mechanisms have a large deployment in remote
   access applications and many IT departments have requirements for
   these unidirectional authentication mechanisms.

1.1 Extended Authentication

   Two-factor authentication and challenge/response schemes like SDI's
   SecurID and RADIUS are forms of authentication that allow a
   gateway, firewall, or network access server to offload the user
   administration and authentication to a central management server.
   IPSec's ISAKMP/Oakley protocol supports certificates (RSA & DSS),
   shared-secret, and Kerberos as authentication methods, but since
   the authentication methods described within this document are only
   unidirectional authentication methods (client to a
   gateway/firewall), they cannot be used by themselves, but must be
   used in conjunction with the other standard ISAKMP authentication

   The technique described within this document utilizes ISAKMP to
   transfer the user's authentication information (name, password) to

R. Pereira                                                    [Page 2]

Internet Draft                                                  Nov-98

   the gateway/firewall (edge device) in a secured ISAKMP message. The
   edge device would then use either the appropriate protocol (RADIUS,
   SecurID, OTP) to authenticate the user.  This allows the
   authentication server to be within the private network that the
   edge device is protecting.

1.2 Reader Prerequisites

   It is assumed that the reader is familiar with the terms and
   concepts described in the "Security Architecture for the Internet
   Protocol" [ArchSec] and "IP Security Document Roadmap" [Thayer97]

   Readers are advised to be familiar with both [IKE] and [ISAKMP] as
   well as [IKECFG] since this document is an extension to that

1.3 Specification of Requirements

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD
   NOT", and "MAY" that appear in this document are to be interpreted
   as described in [Bradner97].

2. Extended Authentication Method

   This specification allows for extended authentication by allowing
   an edge device to request extended authentication from an IPSec
   host (end-node), thus forcing the host to respond with its extended
   authentication credentials.  The edge device will then respond with
   a failed or passed message.

   When the edge device requests extended authentication, it will
   specify the type of extra authentication and any parameters
   required for it.  These parameters MAY be the attributes that it
   requires for authentication and they MAY be information required
   for the IPSec host's reply (e.g. challenge string).

   The last message is simply a reply back from the edge device
   denoting failure or success.  The reply MAY have some textual
   information describing the reason for the failure or success.  The
   edge device MAY also request another authentication, like SecurID's
   next PIN request, where the user is required to enter the next
   passcode to further verify itself.

   As with CHAP [CHAP], this protocol can also be used to periodically
   authenticate the user during the lifetime of a security

R. Pereira                                                    [Page 3]

Internet Draft                                                  Nov-98

   If the IPSec host does not have support for the authentication
   method requested by the edge device, then it would send back a
   reply with empty attributes, thus failing the authentication but
   completing the transaction.  The last exchange (SET/ACK) MUST also
   be completed.

   Here are some types of extended authentication that this
   specification supports;

2.1 Simple Authentication

   Where a user name and password are required for authentication.

   IPSec Host                                              Edge Device
   --------------                                    -----------------
                          <-- REQUEST(TYPE=RADIUS NAME="" PASSWORD="")
   REPLY(TYPE=RADIUS NAME="joe" PASSWORD="foobar") -->
                                                    <-- SET(STATUS=OK)
   ACK() -->

2.2 Challenge/Response

   Where a challenge from the edge device must be incorporated with
   the reply.  This makes each reply different.

   IPSec Host                                              Edge Device
   --------------                                    -----------------
                          <-- REQUEST(TYPE=RADIUS NAME="" PASSWORD="")
   REPLY(TYPE=RADIUS NAME="joe" PASSWORD="foobar") -->
                            <-- REQUEST(TYPE=RADIUS CHALLENGE="123456"
                                        NAME="" PASSWORD="" REQ_NUM=2)
   REPLY(TYPE=RADIUS NAME="joe" PASSWORD="0985124") -->
                                                    <-- SET(STATUS=OK)
   ACK() -->

   If, however, the edge device knows that a challenge will be
   required it may skip the first exchange as follows:

   IPSec Host                                              Edge Device
   --------------                                    -----------------
                            <-- REQUEST(TYPE=RADIUS CHALLENGE="123456"
                                                  NAME="" PASSWORD="")
   REPLY(TYPE=RADIUS NAME="joe" PASSWORD="0985124") -->
                                                    <-- SET(STATUS=OK)
   ACK() -->

R. Pereira                                                    [Page 4]

Internet Draft                                                  Nov-98

2.3 Two-Factor Authentication

   This authentication method combines something the user knows (their
   password) and something that the user has (a token card).

   IPSec Host                                             Edge Device
   --------------                                   -----------------
                                       <-- REQUEST(TYPE=AXENT NAME=""
                                             PASSWORD="" PASSCODE="")
    PASSWORD="foobar" PASSCODE="3412") -->
                                                    <-- SET(STATUS=OK)
   ACK() -->

   Some mechanisms allow for another optional request of the passcode.

   IPSec Host                                              Edge Device
   --------------                                    -----------------
                                      <-- REQUEST(TYPE=SECURID NAME=""
                                              PASSWORD="" PASSCODE="")
    PASSWORD="foobar" PASSCODE="323415") -->
                          <-- REQUEST(TYPE=SECURID NAME="" PASSWORD=""
                                                PASSCODE="" REQ_NUM=2)
    PASSWORD="foobar" PASSCODE="513212") -->
                                                    <-- SET(STATUS=OK)
   ACK() -->

2.4 One-Time-Password

   Similar to the Challenge/Response method, this method allows
   authentication that is secure against passive attacks based on
   replaying captured passwords.

   IPSec Host                                              Edge Device
   --------------                                    -----------------
                   <-- REQUEST(TYPE=OTP CHALLENGE="otp-md5 499 ke1234"
                                                  NAME="" PASSWORD="")
    PASSWORD="5bf0 75d9 959d 036f") -->
                                                    <-- SET(STATUS=OK)
   ACK() -->

3. Extensions to ISAKMP-Config

   This protocol uses the mechanisms described in ISAKMP-Config
   [IKECFG] to accomplish its authentication transaction.

R. Pereira                                                    [Page 5]

Internet Draft                                                  Nov-98

   All ISAKMP-Config messages in an extended authentication
   transaction MUST contain the same ISAKMP-Config message ID.

   This protocol can therefore be used in conjunction with any
   existing basic ISAKMP authentication method as defined in [IKE].
   If mutual authentication is not required, then the phase 1
   negotiation SHOULD use an authentication method of shared-secret
   and have that shared-secret be null.  This, is however, NOT
   suggested since the edge-device is NOT authenticated.

   This authentication MUST be used after a phase 1 exchange has
   completed and before a phase 2 exchange.  The Transaction exchange
   is therefore attached (appended) to the phase 1 exchanges
   (MainMode, AggressiveMode).  If the extended authentication fails,
   then the phase 1 SA MUST be deleted.

   The following are extensions and/or clarifications to the ISAKMP-
   Config [IKECFG] specification to support Extended Authentication.

3.1 Message Types

   Type                        Value
   --------------------------  -----------------------------
    ISAKMP_CFG_REQUEST         ( as defined in [IKECFG] )
    ISAKMP_CFG_REPLY           ( as defined in [IKECFG] )
    ISAKMP_CFG_SET             ( as defined in [IKECFG] )
    ISAKMP_CFG_ACK             ( as defined in [IKECFG] )

   o ISAKMP_CFG_REQUEST - This message is sent from an edge device to
     an IPSec host trying to request extended authentication.
     Attributes that it requires sent back in the reply MUST be
     included with a length of zero (0).  Attributes required for the
     authentication reply, such as a challenge string MUST be
     included with the proper values filled in.

   o ISAKMP_CFG_REPLY - This message MUST contain the filled in
     authentication attributes that were requested by the edge

   o ISAKMP_CFG_SET - This message is sent from an edge device and is
     only used, within the scope of this document, to state the
     success of the authentication.  This message MUST only include
     the success of failure of the authentication and MAY contain
     some clarification text.

   o ISAKMP_CFG_ACK - This message is sent from the IPSec host
     acknowledging receipt of the authentication result.  Its

R. Pereira                                                    [Page 6]

Internet Draft                                                  Nov-98

     attributes are not relevant and MAY be skipped entirely, thus
     not attributes SHOULD be included.  This last message in the
     authentication transaction is used solely as an acknowledgement
     of the previous message and to eliminate problems with
     unacknowledged messages over UDP.

3.2 Attributes

    Attribute                 Value      Type
    ---------------------     ------     ---------------------
    XAUTH_TYPE                13         Basic
    XAUTH_USER_NAME           14         Variable ASCII string
    XAUTH_USER_PASSWORD       15         Variable ASCII string
    XAUTH_PASSCODE            16         Variable ASCII string
    XAUTH_MESSAGE             17         Variable ASCII string
    XAUTH_CHALLENGE           18         Variable ASCII string
    XAUTH_DOMAIN              19         Variable ASCII string
    XAUTH_STATUS              20         Basic
    XAUTH_REQ_NUMBER          21         Basic

   o XAUTH_TYPE - The type of extended authentication requested whose
     values are described in the next section.  This is a mandatory
     attribute for the ISAKMP_CFG_REQUEST and ISAKMP_CFG_REPLY

   o XAUTH_USER_NAME - The user name MAY be any unique identifier of
     the user such as a login name, an email address, or a X.500
     Distinguished Name.

   o XAUTH_USER_PASSWORD - The user's password.

   o XAUTH_PASSCODE - A token card's passcode.  This SHOULD only be
     used when the password attribute is also used.

   o XAUTH_MESSAGE - A textual message from an edge device to an
     IPSec host.  This message MAY be displayed to the user to notify
     them of the reason why authentication failed or succeed.

   o XAUTH_CHALLENGE - A challenge string sent from the edge device
     to the IPSec host for it to include in its calculation of a
     password.  This attribute SHOULD only be sent in an
     ISAKMP_CFG_REQUEST message.

   o XAUTH_DOMAIN - The domain to be authenticated in.  This value
     will have different meaning depending on the authentication

R. Pereira                                                    [Page 7]

Internet Draft                                                  Nov-98

   o XAUTH_STATUS - A variable that is used to denote authentication
     success (OK=1) or failure (FAIL=0).  This is a mandatory
     attribute for the ISAKMP_CFG_SET message.

   o XAUTH_REQ_NUMBER - The number of times that a request has been
     made, including the current request.  The default value is one
     (1) and thus does not have to be included.  This attribute is
     used to denote that an authentication transaction has had to
     have another authentication request.  The IPSec host should
     notice that this is not a retransmit of the original request,
     but that this is yet another request.  This attribute MUST only
     be included in the ISAKMP_CFG_REQUEST message.

3.3 Authentication Types

     Value         Authentication Required
     -----         ---------------------------------
       0           Generic
       1           RADIUS
       2           OTP
       3           NT Domain
       4           Unix Login
       5           SDI SecurID
       6           AXENT Defender
       7           LeeMah InfoCard
       8           ActiveCard
       9           Secure Computing Enigma (DES Gold)
      10           TACACS
      11           TACACS+
      12           S/KEY
      13           NDS (Netware Directory Services)
      14           DIAMETER
      15           LDAP
      16-32767     Reserved for future use
      32768-65535  Reserved for private use

   o Generic - A catch-all type that allows for future extensibility
     and a generic mechanism to request authentication information.
     This method allows for any type of extended authentication.

   o RADIUS - A RADIUS [RADIUS] server requires at least a user name
     and a password, but since RADIUS may be proxying for another
     type of authentication method, both the request and the reply
     MAY be like any of the other extended authentication types.

R. Pereira                                                    [Page 8]

Internet Draft                                                  Nov-98

   o OTP - One-Time-Passwords as defined in [OTP] uses a challenge
     string to request a certain generated password.  The request
     SHOULD contain a user name, password and a challenge string
     while the reply MUST contain the user name and the generated
     password.  The challenge string is formatted as defined in

   o NT Domain - This authentication type provides for user
     authentication by login into a Windows NT(r) domain.  The
     request SHOULD contain empty user name, password and domain
     attributes.  The reply MUST contain all of these attributes
     filled in.  The domain attribute is optional for both messages,
     and SHOULD NOT be included in the reply if it isn’t included in
     the request.

   o Unix Login - Much like the NT Domain authentication type, but
     this will authenticate the user to a Unix(r) workstation.

   o SDI SecurID, AXENT Defender, LeeMah InfoCard, ActiceCard,
     Enigma/DES Gold - All of these (and others) use smart cards to
     generate a 'passcode' to authenticate the user.  This passcode
     combined with the user's password provides stronger
     authentication than just passwords.  The response MUST include
     the user name, password and the token card's passcode. This
     authentication type MIGHT also include a challenge string in the

   o TACACS - Defined in [TACACS], this authentication protocol was
     the precursor to RADIUS, thus the same rules apply.

   o TACACS+ - Defined in [TACACS+], this authentication protocol is
     an updated version of the original TACACS protocol, thus the
     same rules apply.

   o S/KEY - This one-time-password scheme defined in [SKEY] was the
     precursor to OTP, thus the same rules apply.

   o NDS - Much like the NT Domain authentication type, but this will
     authenticate the user to a NetWare Directory server.

   o DIAMETER - The next generation RADIUS protocol that is defined
     in [DIAMETER].  The same rules as RADIUS apply.

4. Other Scenarios for Extended Authentication

   Although this document described a scenario where an IPSec host
   (eg. mobile user) was being authenticated by an edge device (eg.

R. Pereira                                                    [Page 9]

Internet Draft                                                  Nov-98

   firewall/gateway), the methods described can also be used for edge
   device to edge device authentication as well as IPSec host to IPSec
   host authentication.

5. Security Considerations

   Care should be taken when sending sensitive information over public
   networks such as the Internet.  A user's password should never be
   sent in the clear and when sent encrypted, the destination MUST
   have been previously authenticated.  The use of ISAKMP-Config
   [IKECFG] addresses these issues.

6. References

   [Bradner97]    S. Bradner, "Key words for use in RFCs to Indicate
                  Requirement Levels", RFC2119

   [CHAP]         W. Simpson, "PPP Challenge Handshake Authentication
                  Protocol (CHAP)", RFC1994

   [DIAMETER]     P. Calhoun, A. Rubens, "DIAMETER - Base Protocol",

   [IKE]          D. Harkins, D. Carrel, "The Internet Key Exchange
                  (IKE)", draft-ietf-ipsec-isakmp-oakley-07

   [IKECFG]       R. Pereira, "The ISAKMP Configuration Method",

   [RADIUS]       C. Rigney, A. Rubens, W. Simpson, S. Willens,
                  "Remote Authentication Dial In User Service
                  (RADIUS)", RFC2138

   [OTP]          N. Haller, C. Metz, "A One-Time Password System",

   [SKEY]         N. Haller, "The S/KEY One-Time Password System",

   [TACACS]       C. Finseth, "An Access Control Protocol, Sometimes
                  Called TACACS", RFC1492

   [TACACS+]      D. Carrel, L. Grant, "The TACACS+ Protocol Version
                  1.77", draft-grant-tacacs-01.txt

   [OTPEXT]       C. Metz, "OTP Extended Responses", RFC 2243

R. Pereira                                                   [Page 10]

Internet Draft                                                  Nov-98

7. Editor's Address

     Roy Pereira
     TimeStep Corporation
     +1 (613) 599-3610 x 4808

   The IPSec working group can be contacted via the IPSec working
   group's mailing list (ipsec@tis.com) or through its chairs:

     Robert Moskowitz
     Internal Computer Security Association

     Theodore Y. Ts'o
     Massachusetts Institute of Technology

8. Full Copyright Statement

   Copyright (C) The Internet Society (1998).  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.

   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

R. Pereira                                                   [Page 11]