Cryptology ePrint Archive: Report 2002/059

Universally Composable Notions of Key Exchange and Secure Channels

Ran Canetti and Hugo Krawczyk

Abstract: Recently, Canetti and Krawczyk (Eurocrypt 2001) formulated a notion of security for key-exchange (KE) protocols, called SK-security, and showed that this notion suffices for constructing secure channels. Their model and proofs, however, do not suffice for proving more general composability properties of SK-secure KE protocols.

We show that while the notion of SK-security is strictly weaker than a fully-idealized notion of key exchange security, it is sufficiently robust for providing secure composition with arbitrary protocols. In particular, SK-security guarantees the security of the key for any application that desires to set-up secret keys between pairs of parties. We also provide new definitions of secure-channels protocols with similarly strong composability properties, and show that SK-security suffices for obtaining these definitions.

To obtain these results we use the recently proposed framework of "universally composable (UC) security." We also use a new tool, called "non-information oracles," which will probably find applications beyond the present case. These tools allow us to bridge between seemingly limited indistinguishability-based definitions such as SK-security and more powerful, simulation-based definitions, such as UC-security, where general composition theorems can be proven. Furthermore, based on such composition theorems we reduce the analysis of a full-fledged multi-session key-exchange protocol to the (simpler) analysis of individual, stand-alone, key-exchange sessions.

Category / Keywords: cryptographic protocols / Key Exchange, Cryptographic Protocols, Proofs of Security,

Publication Info: Extended abstract of this work appears in the proceedings of Eurocrypt 2002.

Date: received 13 May 2002

Contact author: canetti at watson ibm com

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Version: 20020514:200902 (All versions of this report)

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