International Association for Cryptologic Research
In this paper the researcher recently improved smooth projective hash functions in order to build one-round Password-Authenticated Key Exchange protocols (PAKE). To achieve security in the UC framework they allowed the simulator to extract the hashing key, which required simulation-sound non-interactive zero-knowledge proofs that are unfortunately inefficient. The authors improve the way the latter extractability is obtained by introducing the notion of Trapdoor Smooth Projective Hash Function (TSPHF). A TSPHF is an SPHF with a trapdoor, which may not allow to recover the complete hashing key, but which still allows to compute the hash value, which is enough for an application to PAKE with UC-security against static corruptions.