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rfc:rfc4478

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.

Nir Experimental [Page 1] 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.

Nir Experimental [Page 2] RFC 4478 Repeated Authentication in IKEv2 April 2006

 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.

Nir Experimental [Page 3] RFC 4478 Repeated Authentication in IKEv2 April 2006

 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

Nir Experimental [Page 4] RFC 4478 Repeated Authentication in IKEv2 April 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM 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.

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 pertain to the implementation or use of the technology described in
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 The IETF invites any interested party to bring to its attention any
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 this standard.  Please address the information to the IETF at
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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Nir Experimental [Page 5]

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