Compact Authenticated Key Exchange from Bounded CCA-Secure KEM

How to reduce communication complexity is a common important issue to design cryptographic protocols. This paper focuses on authenticated key exchange (AKE). Several AKE schemes have been studied, which satisfy strong security such as exposure-resilience in the standard model (StdM). However, there is a large gap on communication costs between schemes in the StdM and in the random oracle model. In this paper, we show a generic construction that is significantly compact (i.e., small communication cost) and secure in the StdM. We follow an existing generic construction from key encapsulated mechanism (KEM). Our main technique is to use a bounded chosen-ciphertext secure KEM instead of an ordinary chosen-ciphertext secure KEM. The communication cost can be reduced to half by this technique, and we achieve the most compact AKE scheme in the StdM. Moreover, our construction has instantiations under wider classes of hardness assumptions (e.g., subset-sum problems and multi-variate quadratic systems) than existing constructions. This work pioneers the first meaningful application of bounded chosen-ciphertext secure KEM.