Internet Engineering Task Force R. Pereira
IP Secure Remote Access Working Group Cisco Systems
Internet Draft S. Beaulieu
Expires May 2000 TimeStep Corporation
December 1999
Extended Authentication within ISAKMP/Oakley (XAUTH)
<draft-ietf-ipsec-isakmp-xauth-06.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
This document is a submission to the IETF Internet Protocol Secure
Remote Access (IPSRA) Working Group. Comments are solicited and
should be addressed to the working group mailing list (ietf-
ipsra@vpnc.org) or to the editor.
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Copyright Notice
Copyright (C) The Internet Society (1998-1999). All Rights
Reserved.
R. Pereira, S. Beaulieu [Page 1]
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Abstract
This document describes a method for using existing unidirectional
authentication mechanisms such as RADIUS, SecurID, and OTP within
IPSec's ISAKMP protocol. The purpose of this draft is not to
replace or enhance the existing authentication mechanisms described
in [IKE], but rather to allow them to be extended using legacy
authentication mechanisms.
Table of Contents
1 Introduction.......................................................2
1.1 Changes Since Last Revision......................................3
1.2 Extended Authentication..........................................3
1.3 Reader Prerequisites.............................................4
1.4 Specification of Requirements....................................4
2 Vendor ID..........................................................4
3 Extended Authentication Method.....................................4
3.1 Simple Authentication............................................6
3.2 Challenge/Response...............................................6
3.3 Two-Factor Authentication........................................7
3.4 One-Time-Password................................................7
3.5 User Previously Authenticated....................................8
3.6 Other Useful Examples............................................8
4 Extensions to ISAKMP-Config........................................9
4.1 Message Types....................................................9
4.2 Attributes......................................................10
4.3 Authentication Types............................................11
5 Authentication Method Types.......................................12
6 Other Scenarios for Extended Authentication.......................13
7 Extensibility.....................................................13
8 Security Considerations...........................................14
9 References........................................................15
10 Acknowledgements.................................................16
11 Authors' Addresses...............................................17
11 Expiration.......................................................17
12 Full Copyright Statement.........................................17
Appendix A..........................................................19
1 Introduction
The following technique allows IPSec's ISAKMP/Oakley [IKE] protocol
to support extended authentication mechanisms like two-factor
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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 Changes Since Last Revision
o The last revision of this document was published in the IPSec
Working Group as
<draft-ietf-ipsec-isakmp-xauth-05.txt>
o Moved XAUTH Attribute ID numbers to private range of Isakmp-
Config draft to avoid future collisions.
o Added a Feature / Vendor ID.
o Removed all of the authentication types which can use Generic.
o Made XAUTH_TYPE optional, with the default set to Generic if not
present.
o Clarified the text which allows for a remote peer to abort in the
middle of a transaction.
o Expanded on Security Considerations.
1.2 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
methods.
The technique described within this document utilizes ISAKMP to
transfer the user's authentication information (name, password) to
the gateway/firewall (edge device) in a secured ISAKMP message. The
edge device would then use either the appropriate protocol (RADIUS,
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SecurID, OTP) to authenticate the user. This allows the
authentication server to be within the private network that the
edge device is protecting.
1.3 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]
documents.
Readers are advised to be familiar with both [IKE] and [ISAKMP] as
well as [IKECFG] since this document is an extension to that
document.
1.4 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 Vendor ID
XAUTH currently uses attribute numbers from the private ranges of
both [IKE] and [IKECFG]. In order to ensure interoperability with
future and past implementations of XAUTH a Vendor ID has been
added. The Vendor ID payload is sent during the phase 1 exchange
as per [ISAKMP]. The Vendor ID for this revision of XAUTH is a
truncated MD5 hash of the following ASCII text string: "draft-ietf-
ipsra-isakmp-xauth-06.txt" without the quotation marks.
Vendor ID = 0x09002689DFD6B712
If an implementation receives the aforementioned Vendor ID, it can
assume that the peer also has implemented this protocol and
therefore is a "mutually consenting party".
If this document advances to the standard-track, then new numbers
will be assigned by IANA from the appropriate number spaces of
[IKE] and [IKECFG], thus eliminating the need for a Vendor ID
payload.
3 Extended Authentication Method
This specification allows for extended authentication by allowing
an edge device to request extended authentication from an IPSec
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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 Extended Authentication transaction is terminated either when
the edge device starts a SET/ACK exchange which includes an
XAUTH_STATUS attribute or when the remote device sends a
XAUTH_STATUS attribute in a REPLY message. Please note that a
remote device can not set XAUTH_STATUS to anything but FAIL.
The edge device MAY request multiple different authentication
transactions within one Extended Authentication transaction. This
is done by having multiple REQUEST/REPLY pairs, initiated by the
edge device, before the transaction is terminated as described
above. Each REQUEST/REPLY pair MAY have a different value for
XAUTH_TYPE.
As with CHAP [CHAP], this protocol can also be used to periodically
authenticate the user during the lifetime of a security
association.
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 the XAUTH_STATUS attribute set to FAIL, thus failing
the authentication but completing the transaction.
The Extended Authentication mechanism does not effect the nature of
the phase 1 authentication mechanism in any way. Both peers MUST
authenticate each other via the authentication methods described in
[IKE]. There are Security Considerations involved in one of the
authentication methods in [IKE] and this is described in "Security
Considerations" below.
This method provides unidirectional authentication only, meaning
that only one device is authenticated using both IKE authentication
methods and Extended Authentication.
Here are some types of extended authentication that this
specification supports:
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3.1 Simple Authentication
Where a user name and password are required for authentication.
IPSec Host Edge Device
-------------- -----------------
<-- REQUEST(NAME="" PASSWORD="")
REPLY(NAME="joe" PASSWORD="foobar") -->
<-- SET(STATUS=OK)
ACK(STATUS) -->
Some authentication mechanisms hide the user password by some type
of encryption mechanism.
IPSec Host Edge Device
-------------- -----------------
<-- REQUEST(TYPE=RADIUS-CHAP CHALLENGE="123456"
NAME="" PASSWORD="")
REPLY(TYPE=RADIUS-CHAP NAME="joe" PASSWORD="E4901AB7") -->
<-- SET(STATUS=OK)
ACK(STATUS) -->
NOTE: This is a conceptual example of RADIUS-CHAP, for a more
detailed example, see Appendix A.
3.2 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(NAME="" PASSWORD="")
REPLY(NAME="joe" PASSWORD="foobar") -->
<-- REQUEST(MESSAGE="Enter your password followed by
your pin number" NAME="" PASSWORD="")
REPLY(NAME="joe" PASSWORD="foobar0985124") -->
<-- SET(STATUS=OK)
ACK(STATUS) -->
If, however, the edge device knows that a challenge will be
required it may skip the first exchange as follows:
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IPSec Host Edge Device
-------------- -----------------
<-- REQUEST(MESSAGE="Enter your password followed by
your pin number" NAME="" PASSWORD="")
REPLY(NAME="joe" PASSWORD="foobar0985124") -->
<-- SET(STATUS=OK)
ACK(STATUS) -->
3.3 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(NAME=""
PASSWORD="" PASSCODE="")
REPLY(NAME="joe"
PASSWORD="foobar" PASSCODE="3412") -->
<-- SET(STATUS=OK)
ACK(STATUS) -->
Some mechanisms allow for another optional request of the passcode.
IPSec Host Edge Device
-------------- -----------------
<-- REQUEST(NAME="" PASSWORD="" PASSCODE="")
REPLY(NAME="joe" PASSWORD="foobar" PASSCODE="323415") -->
<-- REQUEST(NAME="" PASSWORD="" PASSCODE="")
REPLY(NAME="joe" PASSWORD="foobar" PASSCODE="513212") -->
<-- SET(STATUS=OK)
ACK(STATUS) -->
3.4 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="")
REPLY(TYPE=OTP NAME="joe" PASSWORD="5bf0 75d9 959d 036f") -->
<-- SET(STATUS=OK)
ACK(STATUS) -->
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3.5 User Previously Authenticated
Some situations may occur where the edge device has already
authenticated the host and no new authentication is required. This
may happen when either the host or the edge device must rekey an
existing phase 1 SA. It is important that this method not be used,
unless the implementation can be sure that the current phase 1 SA
was created with the same peer as the initial phase 1 SA, which was
previously authenticated using XAUTH. There is currently no way
defined to ensure that two separate phase 1 SAs actually belong to
the same peer. One method suggested is to use the ID from the
phase 1 negotiation (available in Main Mode and Aggressive Mode)
but only if the ID is unique to the user and cannot not be forged.
This concept is herein referred to as "ID-Checking".
Implementation hint:
o In order to accomplish ID-Checking for Phase 1 Authenticated
With a Pre-Shared Key (as defined in [IKE]), the pre-shared key
lookup must be based on the phase 1 ID. Please note that this
method only currently works for Aggressive Mode, and may work
with modes defined in the future. A static IP address could also
be used for shared secret lookup, however, the binding of the
user to XAUTH session would have to use the IP address instead of
the ID.
o In order to accomplish ID-Checking for IKE Phase 1
Authenticated With Signatures (as defined in [IKE]), the
implementation must ensure that the ID provided in the phase 1
exchange matches the ID in the peer's certificate which must be
signed by a trusted third party.
In the situation where the peer does not require additional
authentication, the following method is used.
IPSec Host Edge Device
------------- ----------------
<-- SET(STATUS=OK)
ACK(STATUS) -->
3.6 Other Useful Examples
More useful examples are found in Appendix A.
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4 Extensions to ISAKMP-Config
This protocol uses the mechanisms described in ISAKMP-Config
[IKECFG] to accomplish its authentication transaction. This
protocol uses Configuration Attributes from the private range of
Isakmp-Config [IKECFG]. To ensure interoperability with past and
future versions of Extended Authentication, a Vendor ID is provided
in section 2.
All ISAKMP-Config messages in an extended authentication
transaction MUST contain the same ISAKMP-Config transaction
identifier. The Message ID in the ISAKMP header follows the rules
defined by the ISAKMP-Config protocol.
This protocol can therefore be used in conjunction with any
existing basic ISAKMP authentication method as defined in [IKE].
This authentication MUST be used after a phase 1 exchange has
completed and before any other exchange with the exception of Info
mode exchanges. If the extended authentication fails, then the
phase 1 SA MUST be immediately deleted. The edge device MAY choose
to retry an extended authentication request if the user failed to
be authenticated, but must do so in the same ISAKMP-Config
transaction, and MUST NOT send the SET message until the user is
authenticated, or until the edge device wishes to stop retrying and
fail the user.
Extended Authentication MAY be initiated by the edge device at any
time after the initial authentication exchange. For example,
RADIUS servers may specify that a user only be authenticated for a
certain time period. Once that time period has elapsed (minus a
possible jitter), the edge device may request a new Extended
Authentication exchange. If the Extended Authentication exchange
fails, the edge device MUST tear down all phase 1 and phase 2 SAs
associated with the user.
The following are extensions to the ISAKMP-Config [IKECFG]
specification to support Extended Authentication.
4.1 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
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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 device
or if the proper authentication attributes can not be retrieved,
then this message MUST contain the XAUTH_STATUS attribute with a
value of FAIL.
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
attributes are not relevant and MAY be skipped entirely, thus no
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.
4.2 Attributes
Attribute Value Type
--------------------- ------ ---------------------
XAUTH_TYPE 16520 Basic
XAUTH_USER_NAME 16521 Variable ASCII string
XAUTH_USER_PASSWORD 16522 Variable ASCII string
XAUTH_PASSCODE 16523 Variable ASCII string
XAUTH_MESSAGE 16524 Variable ASCII string
XAUTH_CHALLENGE 16525 Variable ASCII string
XAUTH_DOMAIN 16526 Variable ASCII string
XAUTH_STATUS 16527 Basic
o XAUTH_TYPE - The type of extended authentication requested whose
values are described in the next section. This is an optional
attribute for the ISAKMP_CFG_REQUEST and ISAKMP_CFG_REPLY
messages. If the XAUTH_TYPE is not present, then it is assumed
to be Generic. The XAUTH_TYPE in a REPLY MUST be identical to
the XAUTH_TYPE in the REQUEST. If the XAUTH_TYPE was not present
in the REQUEST, then it MUST NOT be present in the REPLY.
However, an XAUTH transaction MAY have multiple REQUEST/REPLY
pairs with different XAUTH_TYPE values in each pair.
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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.
o XAUTH_MESSAGE - A textual message from an edge device to an IPSec
host. The message may contain a textual challenge or
instruction. An example of this would be "Enter your password
followed by your pin number". The message may also contain a
reason why authentication failed or succeeded. This message
SHOULD be displayed to the user.
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. Typically, the XAUTH_TYPE attribute
dictates how the receiving device should handle the challenge.
For example, RADIUS-CHAP uses the challenge to hide the password.
o XAUTH_DOMAIN - The domain to be authenticated in. This value
will have different meaning depending on the authentication type.
o XAUTH_STATUS - A variable that is used to denote authentication
success (OK=1) or failure (FAIL=0). This attribute MUST be sent
in the ISAKMP_CFG_SET message, in which case it may be set to
either OK or FAIL, and MAY be sent in a REPLY message by a remote
peer, in which case it MUST be set to FAIL.
4.3 Authentication Types
Value Authentication Required
----- ---------------------------------
0 Generic
1 RADIUS-CHAP
2 OTP
3 S/KEY
4-32767 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 which
does not require specific processing, and should be used whenever
possible. This is the default setting if no XAUTH_TYPE is
present.
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o RADIUS-CHAP - RADIUS-CHAP is one method of authentication defined
in [RADIUS] which uses a challenge to hide the password. In
order to use the CHAP functionality defined in [RADIUS], the
XAUTH_TYPE MUST be set to RADIUS-CHAP. For all other methods
defined in [RADIUS] (i.e. PAP), the XAUTH_TYPE MUST be set to
Generic.
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 [OTPEXT].
o S/KEY - This one-time-password scheme defined in [SKEY] was the
precursor to OTP, thus the same rules applies.
5 Authentication Method Types
The following values relate to the ISAKMP authentication method
attribute used in proposals. They optionally allow an XAUTH
implementation to propose use of extended authentication after the
initial phase 1 authentication. Values are taken from the private
use range defined in [IKE] and should be used among mutually
consenting parties. To ensure interoperability and avoid
collisions, a Vendor ID is provided in section 2.
Method Value
------------------------------ -----
XAUTHInitPreShared 65001
XAUTHRespPreShared 65002
XAUTHInitDSS 65003
XAUTHRespDSS 65004
XAUTHInitRSA 65005
XAUTHRespRSA 65006
XAUTHInitRSAEncryption 65007
XAUTHRespRSAEncryption 65008
XAUTHInitRSARevisedEncryption 65009
XAUTHRespRSARevisedEncryption 65010
An Extended Authentication proposal has two characteristics.
The first is the direction of the authentication. Each type
identifies whether the Initiator or the Responder is the device
which should be authenticated using XAUTH. For example
XAUTHInitPreShared is a type which demands that the Initiator be
authenticated.
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Note that an edge device would typically initiate with one of the
following:
o XAUTHRespPreShared
o XAUTHRespDSS
o XAUTHRespRSA
o XAUTHRespRSAEncryption
o XAUTHRespRSARevisedEncryption
and would typically only accept proposals with the following
authentication methods:
o XAUTHInitPreShared
o XAUTHInitDSS
o XAUTHInitRSA
o XAUTHInitRSAEncryption
o XAUTHInitRSARevisedEncryption
The second characteristic is the IKE Authentication method to be
used. The following table illustrates which keywords in the
methods described above relate to which Authentication Methods
described in [IKE] Appendix A.
"PreShared" -> pre-shared key
"DSS" -> DSS signatures
"RSA" -> RSA signatures
"RSAEncryption" -> Encryption with RSA
"RSARevisedEncryption" -> Revised encryption with RSA
6 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.
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.
7 Extensibility
Although this protocol was initially developed for the corporate
"Road Warrior" with a dynamic IP address to connect to a corporate
Net, there may be certain applications where static IP addresses
are used by the "Road Warrior" or where this protocol is used in a
non remote-user environment where the IP address is static. There
are Security Considerations for certain applications of this
protocol in certain deployment scenarios. Please consult the
"Security Considerations" section below for more detail.
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[IKE] defines many different ways to authenticate a user and
generate keying material. There are two basic phase 1 modes
defined: Main Mode and Aggressive Mode. There are also at least 5
different authentication schemes which can be used with each mode.
New authentication schemes are being developed and surely more will
be standardized in the future. Similarly new phase 1 modes are
being proposed to address weaknesses or missing functionality in
Main Mode and/or Aggressive mode.
It is for this reason that XAUTH was designed to be fully
extensible. Since XAUTH extends the phase 1 authentication
provided by [IKE], it is an important design goal that a legacy
user authentication scheme in IPsec be able to use the strengths of
current and future authentication and key generation schemes.
XAUTH accomplishes this by working with all modes which allow the
negotiation of a phase 1 authentication method in ISAKMP. Any new
authentication methods defined in the future which are not
addressed by this document need simply to take values from the
"consenting parties" ranges of [IKE]. Such an example would be the
introduction of Encryption with El-Gamal and Revised Encryption
with El-Gamal which were introduced in [IKEv2] which is a proposed
standard.
Furthermore, any new modes defined, such as [HYBRID] and Base Mode
[BASE], will automatically be able to use the functionality of
XAUTH as no new numbers are needed.
Finally, any new or forgotten Legacy User Authentication Schemes
which are not part of XAUTH can be easily incorporated by taking
numbers from the "consenting parties" ranges of XAUTH, or by
requesting reserved numbers from IANA.
8 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.
The protocol described in this memo strictly extends the
authentication methods described in [IKE]. It does not in any way
affect the authenticated nature of the phase 1 security
association. In fact, this protocol heavily relies on the
authenticated nature of the phase 1 SA. Without complete phase 1
authentication, this protocol does not provide *any* authentication
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at all, since it becomes easily vulnerable to Man-in-the-Middle
(MitM) attacks.
This protocol was designed to be extensible, and can be used in
many possible combinations of phase 1 Modes and authentication
methods. However, certain combinations of scenarios could lead to
weaker than desired security, and are therefore discouraged.
When using XAUTH with Pre-Shared keys, where the peer's IP address
is dynamic, Main Mode SHOULD NOT be used, and is STRONGLY
DISCOURAGED. In this particular scenario, the phase 1
authentication becomes suspect as the administrator has little
choice but to use one single Shared-Key for all users, and group-
shared keys are susceptible to "social engineering attacks".
However, the choice of implementation of this functionality is left
up to the implementers of this protocol. There may be some
applications where this functionality is desired. Some examples
are: proof of concept deployments and small deployments where the
proper management of a group shared-key is less difficult.
If at some point restrictions are introduced in one of the IPsec
Standard RFC documents which prohibit the use of group pre-shared
keys, then this protocol will, by default, conform, and these
Security Considerations will no longer be of concern.
9 References
[Bradner97] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC2119
[BASE] Y. Dayan, S. Bitan, "IKE Base Mode", draft-ietf-
ipsec-ike-base-mode-01.txt
[CHAP] W. Simpson, "PPP Challenge Handshake Authentication
Protocol (CHAP)", RFC1994
[DIAMETER] P. Calhoun, A. Rubens, "DIAMETER - Base Protocol",
draft-calhoun-diameter-02.txt
[HYBRID] M. Litvin, R. Shamir, T. Zegman, "A Hybrid
Authentication Mode for IKE", draft-ietf-ipsec-
isakmp-hybrid-auth-02
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[IKE] D. Harkins, D. Carrel, "The Internet Key Exchange
(IKE)", RFC2409
[IKEv2] D. Harkins, D. Carrel, "The Internet Key Exchange
(IKE)", draft-ietf-ipsec-ike-00.txt
[IKECFG] R. Pereira, "The ISAKMP Configuration Method",
draft-ietf-ipsec-isakmp-cfg-05
[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",
RFC1938
[SKEY] N. Haller, "The S/KEY One-Time Password System",
RFC1760
[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
10 Acknowledgements
The authors would like to thank Tamir Zegmen, Moshe Litven, Dan
Harkins and all those from the IPsec community who have helped
improve the XAUTH protocol either. We would also like to thank Tim
Jenkins, Ajai Puri, Laurie Shields, Andrew Krywaniuk, Gabriela
Dinescu, Paul Kierstead and Scott Fanning for their continued
support, and many sanity checks along the way.
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11 Authors' Addresses
Roy Pereira
<royp@cisco.com>
Cisco Systems
+1 (613) 788-7207
Stephane Beaulieu
<sbeaulieu@timestep.com>
TimeStep Corporation
+1 (613) 599-3610 x 4709
The IPSRA working group can be contacted via the IPSec working
group's mailing list (ietf-ipsra@vpnc.org) or through its chairs:
Roy Pereira
royp@cisco.com
Cisco Systems
Sara Bitan
sarab@radguard.com
Radguard
11 Expiration
This draft expires May, 2000
12 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.
R. Pereira, S. Beaulieu [Page 17]
Internet Draft Dec-99
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.
R. Pereira, S. Beaulieu [Page 18]
Internet Draft Dec-99
Appendix A
This appendix gives more useful examples of Extended
Authentication.
Secure ID Next PIN mode
=======================
Ipsec Client Ipsec Gateway
------------ -------------
<-- REQUEST(Username = '', Password = '')
REPLY(Username = 'joe', Password = '1637364856') -->
<-- REQUEST(Password = '', XAUTH_MESSAGE = 'The system has
assigned you a new PIN, do you wish to see it now?')
REPLY(Password = 'y') -->
<-- REQUEST(Password = '', XAUTH_MESSAGE
= 'Your new pin is 1234'
REPLY(Password = '1234764456') -->
<-- SET(XAUTH_STATUS = OK)
ACK(XAUTH_STATUS) -->
RADIUS Chap Challenge
=====================
Ipsec Client Ipsec Gateway
------------ -------------
<-- REQUEST(TYPE = RADIUS-CHAP, Username = '', Password = '',
Challenge = 0x01020304050607080910111213141516)
REPLY(TYPE = RADIUS-CHAP, Username = 'joe', Password =
'0xaa11121314151617181920212223242526') -->
<-- SET(XAUTH_STATUS = OK)
ACK(XAUTH_STATUS) -->
where the Challenge in the REQUEST is the random number generated
by the edge device, and the Password in the reply contains the ID
used to calculate the hash 'aa' concatenated with the hash of the
(ID+challenge+secret)
R. Pereira, S. Beaulieu [Page 19]
