Internet Engineering Task Force R. Pereira
IP Security Working Group TimeStep Corporation
Internet Draft
Expires in six months
February 11, 1998
Extended Authentication Within ISAKMP/Oakley
<draft-ietf-ipsec-isakmp-xauth-01.txt>
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
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Distribution of this memo is unlimited.
Abstract
This document describes a method for using existing unidirectional
authentication mechanisms such as RADIUS, SecureID, and OTP with
ISAKMP.
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Table of Contents
1. Introduction...................................................2
1.1 Extended Authentication.....................................2
1.2 Specification of Requirements...............................3
2. Authentication Types...........................................3
2.1 Simple Authentication.......................................3
2.2 Challenge/Response..........................................3
2.3 Two-Factor Authentication...................................3
2.4 One-Time-Password...........................................4
3. Interaction with ISAKMP........................................4
3.1 Exchanges...................................................5
4. Extensions to ISAKMP-Config....................................5
4.1 NOTIFY Types................................................6
4.2 Attributes..................................................6
4.3 Authentication Types........................................7
5. Security Considerations........................................8
6. References.....................................................9
7. Editor's Address...............................................9
1. Introduction
The following technique allows IPSec's ISAKMP/Oakley 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
SecureID 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 authentication methods.
The technique described within this document utilizes ISAKMP to
transfer the user's authentication information (name, password) to
the gateway/firewall in a secured ISAKMP message. The
gateway/firewall would then use either the appropriate protocol
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(RADIUS, SecureID, OTP) to authenticate the user. This allows the
authentication server to be within the private network that the
gateway/firewall is protecting.
1.2 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. Authentication Types
2.1 Simple Authentication
Where a user name and password are required for authentication.
IPSec Host Edge Device
-------------- -----------------
<-- CFG-REQUEST(RADIUS NAME PASSWORD)
CFG-REPLY(RADIUS NAME PASSWORD) -->
<-- CFG-AUTH-OK()
2.2 Challenge/Response
Where a challenge from the gateway/firewall must be incorporated
with the reply. This makes each reply different.
IPSec Host Edge Device
-------------- -----------------
<-- CFG-REQUEST(RADIUS CHALLENGE NAME PASSWORD)
CFG-REPLY(RADIUS NAME PASSWORD) -->
<-- CFG-AUTH-OK()
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
-------------- -----------------
<-- CFG-REQUEST(SECUREID NAME PASSWORD PASSCODE)
CFG-REPLY(SECUREID NAME PASSWORD PASSCODE) -->
<-- CFG-AUTH-OK()
Some mechanisms allow for another request of the passcode;
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IPSec Host Edge Device
-------------- -----------------
<-- CFG-REQUEST(SECUREID NAME PASSWORD PASSCODE)
CFG-REPLY(SECUREID NAME PASSWORD PASSCODE) -->
<-- CFG-REQUEST(SECUREID NAME PASSWORD PASSCODE)
CFG-REPLY(SECUREID NAME PASSWORD PASSCODE) -->
<-- CFG-AUTH-OK()
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
-------------- -----------------
<-- CFG-REQUEST(OTP CHALLENGE NAME PASSWORD)
CFG-REPLY(TOP NAME PASSWORD) -->
<-- CFG-AUTH-OK()
3. Interaction with ISAKMP
This protocol utilizes the mechanisms described in ISAKMP-Config
[Pereira97] to accomplish its request/reply transaction through
ISAKMP.
An edge device (gateway or firewall) may request extended
authentication from a 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.
Example:
IPSec Host Edge Device
-------------- -----------------
<-- CFG-REQUEST(SECUREID NAME PASSWORD PASSCODE)
CFG-REPLY(SECUREID NAME PASSWORD PASSCODE) -->
<-- CFG-AUTH-FAILED()
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 or they MAY be information required for
the IPSec host's reply (eg. challenge string).
The last message, is simply a reply back from the gateway/firewall
denoting failure or passing. The replay MAY have some textual
information describing the reason for the failure or success. The
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gateway/firewall may also request another authentication, like
Secure ID's next PIN request, where the user is required to enter
the next passcode to further verify the user.
3.1 Exchanges
ISAKMP-Config sets forth some guidelines on where these exchanges
may take place. This document will add on to those guidelines in
relation to extended authentication exchanges.
As described in the last section, the edge device requests extended
authentication. This MUST be supported at least in these three
places:
[1] ISAKMP Main Mode in the responder's second message - if the
client's ID is not relevant to decide whether or not to request
extended authentication.
[2] ISAKMP Main Mode in the responder's third message - if the
client's ID is relevant in deciding whether or not to request
extended authentication.
[3] ISAKMP Aggressive mode in the responder's first message - if
identity protection is not required for ISAKMP.
The main reason that only the above three places are valid are
because the client's reply MUST be secured since it will carry
sensitive information like passwords.
In the case of Aggressive Mode, ISAKMP-Config [Pereira97] denotes
that the response be sent in an encrypted InfoMode ISAKMP message
after the Aggressive Mode is done and an ISAKMP SA exists between
the two peers.
The extended authentication exchange MAY also be used in Quick
Mode, but for inter-operability's sake, the methods listed above
MUST be supported.
4. Extensions to ISAKMP-Config
The following are extensions to the ISAKMP-Config [Pereira97]
specification to support Extended Authentication.
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4.1 NOTIFY Types
Type Value
-------------------------- -----------------------------
ISAKMP_CFG_REQUEST ( as defined in [Pereira97] )
ISAKMP_CFG_REPLY ( as defined in [Pereira97] )
ISAKMP_CFG_AUTH_OK 105
ISAKMP_CFG_AUTH_FAILED 106
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 authentication
attributes that were requested by the edge device filled in.
o ISAKMP_CFG_AUTH_OK - This message MAY contain a textual message
in the XAUTH_MESSAGE attribute.
o ISAKMP_CFG_AUTH_FAILED - This message MAY contain a textual
message in the XAUTH_MESSAGE attribute.
4.2 Attributes
Attribute Value Type
--------------------- ------ ---------------------
XAUTH_TYPE 101 Basic
XUATH_USER_NAME 102 Variable ASCII string
XAUTH_USER_PASSWORD 103 Variable ASCII string
XAUTH_PASSCODE 104 Variable ASCII string
XAUTH_MESSAGE 105 Variable ASCII string
XAUTH_CHALLENGE 106 Variable ASCII string
XAUTH_DOMAIN 107 Variable ASCII string
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
messages.
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.
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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 SHOULD 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 or passcode. This attribute SHOULD only be sent in a
ISAKMP_CFG_REQUEST message.
o XAUTH_DOMAIN - The domain to be authenticated in. This value
will have different meaning depending on the authentication
type.
4.3 Authentication Types
Value Authentication Required
----- ---------------------------------
0 Generic
1 RADIUS
2 OTP
3 NT Domain
4 Unix Login
5 SDI SecureID
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)
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 [Radius97] server requires 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.
o OTP - One-Time-Passwords as defined in [Opt96] uses a challenge
string to request a certain generated password. The request
SHOULD contain a user name, password and a challenge string
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while the reply MUST contain the user name and the generated
password. The challenge string is formatted as defined in
[Metz97].
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 isnt 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 SecureID, 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, user password and the token card's passcode.
This authentication type MIGHT also include a challenge string
in the request.
o TACACS - Defined in [Tacacs93], this authentication protocol was
the precursor to RADIUS, thus the same rules apply.
o TACACS+ - Defined in [Tacacs+97], 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 [Skey95] 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.
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
[Pereira97] plus further guidelines outlined in this document
address these issues.
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6. References
[Bradner97] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC2119
[Finseth93] C. Finseth, "An Access Control Protocol, Sometimes
Called TACACS", RFC1492
[Radius97] C. Rigney, A. Rubens, W. Simpson, S. Willens,
"Remote Authentication Dial In User Service
(RADIUS)", RFC2138
[Pereira97] R. Pereira, "The ISAKMP Configuration Method",
draft-ietf-ipsec-isakmp-cfg-02
[Opt96] N. Haller, C. Metz, "A One-Time Password System",
RFC1938
[Skey95] N. Haller, "The S/KEY One-Time Password System",
RFC1760
[Tacacs93] C. Finseth, "An Access Control Protocol, Sometimes
Called TACACS", RFC1492
[Tacacs+97] D. Carrel, L. Grant, "The TACACS+ Protocol Version
1.77", draft-grant-tacacs-01.txt
[Metz97] C. Metz, "OTP Extended Responses", RFC 2243
7. Editor's Address
Roy Pereira
<rpereira@timestep.com>
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
rgm3@icsa.net
ICSA
Theodore Y. Tso
tytso@MIT.EDU
Massachusetts Institute of Technology
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