A new IETF working group has been proposed in the Security Area. The IESG has not made any determination as yet. The following UPDATED draft charter was submitted, and is provided for informational purposes only. Please send your comments to the IESG mailing list (iesg@ietf.org) by October 23rd. +++ Handover Keying (hokey) ========================== Current Status: Proposed Working Group Chair(s): TBD Security Area Director(s): Russ Housley <housley@vigilsec.com> Sam Hartman <hartmans-ietf@mit.edu> Security Area Advisor: Russ Housley <housley@vigilsec.com> Mailing List: hokeyp@opendiameter.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 facilitate inter-authenticator handover and roaming. Some problems that need to be addressed with extensions to EAP keying include: 1) Inter-authenticator handovers require re-execution of EAP authentication even though the same EAP authentication server is used. 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 to 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, a consistent, EAP-method-independent, low-latency re-authentication mechanism is needed. 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 derivations. 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 in current handoff and roaming solutions can be attributed to different trade-offs between computational cost, mobility performance, and security. Specifications are not consistent in the way that the key derivation function (KDF) and KDF parameters are used. Clear direction by the IETF on the topology and construction of a key hierarchy 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 keying," "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 scenario. 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 draft-ietf-eap-keying. 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 use it. 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 technology. HOKEY WG Deliverables ===================== All the specifications will be EAP-method-independent manner and access-technology-agnostic. EAP re-authentication and EAP pre-authentication authenticator are expected to use the same layer and the same protocol as the original EAP authentication used for the authenticator. They will provide enough semantics and guidance so that all SDOs can employ them and preserve cryptographic separation. 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 scenario. 2) A specification of an EMSK-based key hierarchy topology. The specification will include a requirements, one or more 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 protocol specification 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-EAP-authenticator roaming and re-authentication in visited domains that is brokered using inter-domain trust relationships to support efficient inter-domain roaming. 7) A specification for EAP pre-authentication to support low-latency inter-authenticator handoffs. MILESTONES ========== Dec 06 First draft with a problem statement on EAP re-authentication and key management Dec 06 First draft on EMSK-based Keying Hierarchy Feb 07 First draft on EAP Re-authentication and Handover Keying Hierarchy 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 to IESG 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 _______________________________________________ IETF-Announce@ietf.org https://www1.ietf.org/mailman/listinfo/ietf-announce
