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EXPERIMENTAL
Network Working Group Y. Nir
Request for Comments: 4478 Check Point
Category: Experimental April 2006
Repeated Authentication in Internet Key Exchange (IKEv2) Protocol
Status of This Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document extends the Internet Key Exchange (IKEv2) Protocol
document [IKEv2]. With some IPsec peers, particularly in the remote
access scenario, it is desirable to repeat the mutual authentication
periodically. The purpose of this is to limit the time that security
associations (SAs) can be used by a third party who has gained
control of the IPsec peer. This document describes a mechanism to
perform this function.
1. Introduction
In several cases, such as the remote access scenario, policy dictates
that the mutual authentication needs to be repeated periodically.
Repeated authentication can usually be achieved by simply repeating
the Initial exchange by whichever side has a stricter policy.
However, in the remote access scenario it is usually up to a human
user to supply the authentication credentials, and often Extensible
Authentication Protocol (EAP) is used for authentication, which makes
it unreasonable or impossible for the remote access gateway to
initiate the IKEv2 exchange.
This document describes a new notification that the original
Responder can send to the original Initiator with the number of
seconds before the authentication needs to be repeated. The
Initiator SHOULD repeat the Initial exchange before that time is
expired. If the Initiator fails to do so, the Responder may close
all Security Associations.
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RFC 4478 Repeated Authentication in IKEv2 April 2006
Repeated authentication is not the same as IKE SA rekeying, and need
not be tied to it. The key words "MUST", "MUST NOT", "SHOULD",
"SHOULD NOT", and "MAY" in this document are to be interpreted as
described in [RFC2119].
2. Authentication Lifetime
The Responder in an IKEv2 negotiation MAY be configured to limit the
time that an IKE SA and the associated IPsec SAs may be used before
the peer is required to repeat the authentication, through a new
Initial Exchange.
The Responder MUST send this information to the Initiator in an
AUTH_LIFETIME notification either in the last message of an IKE_AUTH
exchange, or in an INFORMATIONAL request, which may be sent at any
time.
When sent as part of the IKE SA setup, the AUTH_LIFETIME notification
is used as follows:
Initiator Responder
------------------------------- -----------------------------
HDR, SAi1, KEi, Ni -->
<-- HDR, SAr1, KEr, Nr, [CERTREQ]
HDR, SK {IDi, [CERT,] [CERTREQ,]
[IDr,] AUTH, SAi2, TSi, TSr} -->
<-- HDR, SK {IDr, [CERT,] AUTH,
SAr2, TSi, TSr,
N(AUTH_LIFETIME)}
The separate Informational exchange is formed as follows:
<-- HDR, SK {N(AUTH_LIFETIME)}
HDR SK {} -->
The AUTH_LIFETIME notification is described in Section 3.
The original Responder that sends the AUTH_LIFETIME notification
SHOULD send a DELETE notification soon after the end of the lifetime
period, unless the IKE SA is deleted before the lifetime period
elapses. If the IKE SA is rekeyed, then the time limit applies to
the new SA.
An Initiator that received an AUTH_LIFETIME notification SHOULD
repeat the Initial exchange within the time indicated in the
notification. The time is measured from the time that the original
Initiator receives the notification.
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A special case is where the notification is sent in an Informational
exchange, and the lifetime is zero. In that case, the original
responder SHOULD allow a reasonable time for the repeated
authentication to occur.
The AUTH_LIFETIME notification MUST be protected and MAY be sent by
the original Responder at any time. If the policy changes, the
original Responder MAY send it again in a new Informational.
The new Initial exchange is not altered. The initiator SHOULD delete
the old IKE SA within a reasonable time of the new Auth exchange.
3. AUTH_LIFETIME Notification
The AUTH_LIFETIME message is a notification payload formatted as
follows:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Protocol ID ! SPI Size ! Notify Message Type !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Lifetime !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Payload Length is 12.
o Protocol ID (1 octet) MUST be 0.
o SPI size is 0 (SPI is in message header).
o Notify Message type is 16403 by IANA.
o Lifetime is the amount of time (in seconds) left before the
peer should repeat the Initial exchange. A zero value
signifies that the Initial exchange should begin immediately.
It is usually not reasonable to set this value to less than 300
(5 minutes) since that is too cumbersome for a user.
It is also usually not reasonable to set this value to more
than 86400 (1 day) as that would negate the security benefit of
repeating the authentication.
4. Interoperability with Non-Supporting IKEv2 Implementations
IKEv2 implementations that do not support the AUTH_LIFETIME
notification will ignore it and will not repeat the authentication.
In that case the original Responder will send a Delete notification
for the IKE SA in an Informational exchange. Such implementations
may be configured manually to repeat the authentication periodically.
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Non-supporting Responders are not a problem because they will simply
not send these notifications. In that case, there is no requirement
that the original Initiator re-authenticate.
5. Security Considerations
The AUTH_LIFETIME notification sent by the Responder does not
override any security policy on the Initiator. In particular, the
Initiator may have a different policy regarding re-authentication,
requiring more frequent re-authentication. Such an Initiator can
repeat the authentication earlier then is required by the
notification.
An Initiator MAY set reasonable limits on the amount of time in the
AUTH_LIFETIME notification. For example, an authentication lifetime
of less than 300 seconds from SA initiation may be considered
unreasonable.
6. IANA Considerations
The IANA has assigned a notification payload type for the
AUTH_LIFETIME notifications from the IKEv2 Notify Message Types
registry.
7. Normative References
[IKEv2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC
4306, December 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Author's Address
Yoav Nir
Check Point Software Technologies
EMail: ynir@checkpoint.com
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RFC 4478 Repeated Authentication in IKEv2 April 2006
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