IKEv2 re-auth: Repeated Authentication in Internet Key Exchange (IKEv2) Protocol
A responder can set a deadline for repeating mutual authentication.
Nir, Y., "Repeated Authentication in Internet Key Exchange (IKEv2) Protocol", RFC 4478, DOI 10.17487/RFC4478, April 2006, <https://www.rfc-editor.org/info/rfc4478>.
@misc{rfc4478,
series = {Request for Comments},
number = 4478,
howpublished = {RFC 4478},
publisher = {RFC Editor},
doi = {10.17487/RFC4478},
url = {https://www.rfc-editor.org/info/rfc4478},
author = {Y. Nir},
title = {{Repeated Authentication in Internet Key Exchange (IKEv2) Protocol}},
pagetotal = 5,
year = 2006,
month = apr,
} RFC text
Contents
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. 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. 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. 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 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. 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ISO Plain Language
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§1Why Repeat Authentication
Some policies require IKEv2 peers to repeat mutual authentication periodically. In remote access, a human may need to provide credentials, often through the Extensible Authentication Protocol (EAP), so the gateway may not be able to initiate the exchange itself.
RFC 4478 lets the original responder tell the original initiator how many seconds remain before authentication must be repeated. The RFC distinguishes this from rekeying an IKE security association.
The gateway can set a time for the user side to authenticate again. This is separate from replacing the keys in an existing security association.
§2The AUTH_LIFETIME Notification
The responder sends an AUTH_LIFETIME notification either in the final message of the IKE_AUTH exchange or in an INFORMATIONAL request. The notification gives the number of seconds before the initiator should repeat the Initial exchange; time is measured from when the initiator receives it.
The initiator SHOULD repeat the exchange before the lifetime ends. A lifetime of zero means to begin immediately. The RFC says values below 300 seconds or above 86400 seconds are usually unreasonable. If the initiator does not re-authenticate, the responder may delete the security associations.
The notification gives the initiator a time limit, in seconds. The initiator should authenticate again before the limit expires; zero means to start right away.
§4Peers Without Support
An IKEv2 implementation that does not support AUTH_LIFETIME ignores the notification and does not repeat authentication because of it. In that case, the original responder sends a Delete notification for the IKE security association.
A responder that does not support this extension simply does not send the notification. An initiator may also require more frequent authentication than the notification requests; the notification does not override its policy.
An older peer may ignore the request. The responder can then delete the security association, while the initiator can still require authentication sooner.
§5Security Policy and IANA
The RFC says the responder's notification does not override the initiator's security policy. An initiator may set reasonable limits on the lifetime it accepts, including rejecting a very short value.
IANA assigned a notification payload type for AUTH_LIFETIME in the IKEv2 Notify Message Types registry.
The initiator remains free to require stricter re-authentication than the responder asks for. IANA assigned a notification type for this message.