[802SEC] FW: [New-work] WG Review: Handover Keying (hokey)
IEEE 802 WG Chairs,
The following new work announcement from the IETF may also be of
interest to your WG members.
From: IESG Secretary [mailto:email@example.com]
Sent: Monday, October 02, 2006 7:30 AM
Subject: [New-work] WG Review: Handover Keying (hokey)
A new IETF working group has been proposed in the Security Area.
The IESG has not made any determination as yet. The following draft
charter was submitted, and is provided for informational purposes only.
Please send your comments to the IESG mailing list
(firstname.lastname@example.org) by October 9.
Handover Keying (hokey)
Current Status: Proposed Working Group
Security Area Director(s):
Russ Housley <email@example.com>
Sam Hartman <firstname.lastname@example.org>
Security Area Advisor:
Russ Housley <email@example.com>
Mailing List: firstname.lastname@example.org
Most deployments of EAP in wireless networks employ an authenticator in
pass-through mode, usually located at the edge, coupled with a backend
AAA/ EAP server. Many EAP methods generate an MSK and an EMSK. The MSK
is used by several EAP lower layers. The EMSK remains at the peer and
server, but it is not presently used in any specifications. Different
EAP lower layers make use of the MSK differently; the most common usage
is to derive Transient Session Keys (TSKs) to provide access link
security in networks (e.g., IEEE 802.11i, IEEE 802.16e), although some
lower layers (e.g., IKEv2) use the MSK for other purposes.
Extensions to current EAP key framework will be needed to support some
envisioned scenarios. Some problems that need to be addressed with
extensions to EAP keying include:
1) Transport of the EAP MSK from the EAP/AAA server to the initial
authenticator means a handover from the initial authenticator to another
authenticator may require re-execution of EAP authentication, even
though the same EAP/AAA server will handle the authentication. Handover
scenarios vary considerably in their fundamental assumptions. In
scenarios where hosts remain connected during the handover period, EAP
authentication need not be in the critical path for handover. However,
there are scenarios where necessary connectivity is not available or
where the EAP does not support "make before break" communications. In
these scenarios, significant handover latency can result. To avoid this
latency, SDOs have employed methods such as context transfer and
anchoring that are inefficient or insecure or both.
2) EAP peers with unexpired keying material from a full EAP exchange
must take part in a full EAP exchange with the same AAA server to extend
a session. While some EAP methods provide fast re-authentication
mechanisms, these procedures require a minimum of one-and-a-half
roundtrips. A consistent, method-agnostic, single roundtrip protocol is
3) EAP generates keys (MSK and EMSK). When the EAP WG updated the
protocol and specified the keying framework, many details regarding the
use of the EMSK were not specified. The EMSK can be used as the root of
a cryptographic key hierarchy, and then the keys in the hierarchy are
used in various ways to provide the needed security services. In order
to ensure that different keys derived from the EMSK are
cryptographically separate and that the key derivations are coordinated
in an acceptable manner, it is important to clearly specify the top of
the topology for the key hierarchy and some guidelines for child key
4) When wireless networks employ AAA infrastructures, the cross-domain
roaming is handled by inter-domain authentication via the "home" AAA/EAP
server. Any authentication must pass through the home server, which
increases latency. Latency can be reduced by establishing a trust
relationship between the EAP peer and the visited domain's AAA/EAP
server. This trust relationship would be brokered by the home EAP/AAA
server. Efficient re-authentication for the EAP peer can be supported
locally within the visited domain.
Some of the inconsistency can be attributed to different trade-offs
between computational cost, mobility performance, and security. However,
clear direction by the IETF on AMSK (also called
USRK) derivation could reduce some of the inconsistencies. However, the
HOKEY WG will not attempt to standardize TSK derivation from the MSK, as
this would interference with work of other SDOs.
The solutions specified by the HOKEY WG fall into several categories,
based on timing and mechanism. The authentication and key management may
occur before handoff, when latency is much less critical. Alternatively,
authentication and key management can occur as part of the handoff,
where latency is critical. Solutions should reduce or eliminate the
number of referrals to AAA servers, and solutions should avoid
re-executing lengthy EAP method exchanges. This may be accomplished by
providing new mechanisms for cryptographic keying material in
combination with a protocol for the timely delivery of appropriate keys
to the appropriate entities. Solutions are expected to include "handover
"low-latency re-authentication," and "pre-authentication."
All solution categories are useful, each supporting different scenarios.
The HOKEY WG may provide multiple solutions, each addressing a different
Solutions specified by the HOKEY WG must:
1) Be responsive to handover and re-authentication latency performance
objectives within a mobile wireless access network.
2) Fulfill the requirements in draft-housley-aaa-key-mgmt and
3) Be independent of the access-technology. Any key hierarchy topology
or protocol defined must be independent of EAP lower layers. The
protocols may require additional support from the EAP lower layers that
4) Accommodate inter-technology heterogeneous handover and roaming.
5) No changes to EAP methods. Any extensions defined to EAP must not
cause changes to existing EAP methods.
In specifying an access-technology-independent solution, media
independent guidelines for SDOs may also be needed to explain how the
keying material and signaling can be employed in a specific access
HOKEY WG Deliverables
All the specifications will be EAP-method-independent manner and
access-technology-agnostic. They will provide enough semantics and
guidance so that all SDOs can employ them and preserve cryptographic
1) A Problem Statement that defines the problem of re-authentication and
key management. The discussion will include security and performance
goals for the solutions. Too often, mobility optimization discussions do
not clearly identify the scenarios that are being addressed; this lack
of clarity often makes it difficult to agree on whether the proposed
optimizations offer real value. To avoid this situation, the Problem
Statement must clearly describe the scenarios that are being addressed,
and the assumptions about the handover environment associated with that
2) A specification of an EMSK-based key hierarchy topology. The
specification will include a requirements, one or more key derivation
function (KDF), and parameters. This is follow-on work EAP (RFC
3748) and EAP keying framework that was developed in the EAP WG.
3) A specification for the derivation of root keys, such as the handover
root key (HRK), to support re-authentication and handover key
management. The HOKEY WG can base these keys on either the MSK or the
EMSK produced by EAP (pick one). If the consensus is to use the EMSK,
then the HRK forms one branch in the EMSK-based key hierarchy. This
specification will describe the properties of each key that is
specified, and the topics must include caching, naming, scope, binding,
storage, and key lifetime.
4) A protocol specification for media-independent, low-latency
re-authentication. The EAP re-authentication mechanism must support
handovers between EAP authenticators. This protocol specification is
expected to employ a re-authentication branch in the key hierarchy.
5) A protocol specification for secure and timely distribution of
cryptographic keys to support roaming and handover. Use of AAA protocols
is preferred, and if used, should leverage existing work if possible
(such as RADEXT WG work on RFC 3576bis and RADIUS cryptographic
algorithm agility). However, if AAA protocols cannot meet the
objectives, other protocols for reactive or proactive distribution or
retrieval of keys by the proper entities is permitted.
6) A specification for inter-domain roaming solutions based on use of
either trust relationships or pre-authentication methods or both.
Dec 06 First draft with a problem statement on EAP re-authentication and
Dec 06 First draft on EMSK-based Keying Hierarchy
Feb 07 First draft on EAP Re-authentication and Handover Keying
Feb 07 First draft on EAP Re-authentication Protocol
Mar 07 First draft on Protocol and Keying Hierarchy for Visited Domain
Handovers and Re-authentication
Mar 07 Submit the problem statement draft to IESG
Mar 07 Submit EMSK-based Keying Hierarchy draft to IESG
Jun 07 First draft on Handover Key Distribution Protocol
Aug 07 Submit EAP Re-authentication and Handover Keying Hierarchy draft
Aug 07 Submit EAP Re-authentication Protocol draft to IESG
Sep 07 Submit Protocol and Keying Hierarchy for Visited Domain Handovers
and Re-authentication draft to IESG
Sep 07 First draft on EAP Pre-authentication Specification for
inter-technology and inter-domain handoffs
Mar 08 Submit EAP Pre-authentication Specification to IESG
Mar 08 Re-charter or shut down WG
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