Relatively-Sound NIZKs and Password-Based Key-Exchange

We define a new notion of relatively-sound non-interactive zeroknowledge (NIZK) proofs, where a private verifier with access to a trapdoor continues to be sound even when the Adversary has access to simulated proofs and common reference strings. It is likely that this weaker notion of relative-soundness suffices in most applications that need simulation-soundness. We show that for certain languages which are diverse groups, and hence allow smooth projective hash functions, one can obtain more efficient single-theorem relatively-sound NIZKs as opposed to simulation-sound NIZKs. We also show that such relatively-sound NIZKs can be used to build rather efficient publiclyverifiable CCA2-encryption schemes. By employing this new publicly-verifiable encryption scheme along with an associated smooth projective-hash, we show that a recent PAKmodel single-round password-based key exchange protocol of Katz and Vaikuntanathan, Proc. TCC 2011, can be made much more efficient. We also show a n...

• Type: Journal
• Year: 2012
• Where: PKC
• Authors: Charanjit S. Jutla, Arnab Roy
• Keywords: Cryptology, Exchange Protocol, Group Elements, Hash Functions, PKC 2012