Universally Composable Notions of Key Exchange and Secure Channels (Extended Abstract)
Ran Canetti, Hugo Krawczyk · 2002
Recently, Canetti and Krawczyk (Eurocrypt'2001) formu- lated a notion of security for key-exchange (ke) protocols, called SK- security, and showed that this notion suffices for constructing secure channels. However, their model and proofs 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 com- posability properties, and show that SK-security suffices for obtaining these definitions. To obtain these results we use the recently proposed framework of uni- versally 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 pow- erful, simulation-based definitions, such as UC security, where general composition theorems can be proven. Furthermore, based on such compo- sition 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.