Cryptology ePrint Archive: Report 2008/376

Session-state Reveal is stronger than Ephemeral Key Reveal: Attacking the NAXOS Authenticated Key Exchange protocol

Cas J.F. Cremers

Abstract: In the papers Stronger Security of Authenticated Key Exchange [LLM07, LLM06], a new security model for key exchange protocols is proposed. The new model is suggested to be at least as strong as previous models for key exchange protocols. In particular, the model includes a new notion of an Ephemeral Key Reveal adversary query, which is claimed in [LLM06, Oka07, Ust08] to be at least as strong as existing definitions of the Session-state Reveal query. We show that for some protocols, Session-state Reveal is strictly stronger than Ephemeral Key Reveal. In particular, we show that the NAXOS protocol from [LLM07, LLM06] does not meet its security requirements if the Session-state Reveal query is allowed in the security model.

Category / Keywords: cryptographic protocols / foundations, security models, key agreement, session-state reveal, ephemeral key reveal

Date: received 3 Sep 2008, last revised 9 Jun 2009

Contact author: cas cremers at inf ethz ch

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Version: 20090609:150628 (All versions of this report)

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