Round-Optimal Password-Based Authenticated Key Exchange
Jonathan I. Katz, Vinod Vaikuntanathan · 2010
We show a general framework for constructing password-based authenticated key-exchange protocols with optimal round complexity — one message per party, sent simultaneously — in the standard model, assuming the existence of a common reference string. When our framework is instantiated using bilinear-map-based cryptosystems, the resulting protocol is also (reasonably) efficient. Somewhat surprisingly, our framework can be adapted to give protocols in the standard model that are universally composable while still using only one (simultaneous) round. 1 Password-Based Authenticated Key Exchange Protocols for authenticated key exchange enable two parties to generate a shared, cryptographically strong key while communicating over an insecure network under the complete control of an adversary. Such protocols are among the most widely used and fundamental cryptographic primitives; indeed, agreement on a shared key is necessary before “higher-level ” tasks such as encryption and message authentication become possible. Parties must share some information in order for authenticated key exchange to be possible. It is well known that shared cryptographic keys — either in the form of public keys or a long,