Paper 2020/207

A Framework for Universally Composable Publicly Verifiable Cryptographic Protocols

Carsten Baum and Bernardo David and Rafael Dowsley

Abstract

The Universal Composability (UC) framework (FOCS '01) is the current gold standard for proving security of interactive cryptographic protocols. Proving security of a protocol in UC is an assurance that the theoretical model of a protocol does not have any obvious bugs, in particular when using it as part of a larger construction. UC allows to reason about complex structures in a bottom-up fashion by talking about the individual components and how they are composed. It thereby simplifies the construction of complex secure protocols. Due to certain design choices of the UC framework, realizing certain security notions such as verifiability is cumbersome and ``obviously secure'' constructions require rather strong and thus in practice expensive individual building blocks. In this work we give the first formal study of Non-Interactive Public Verifiability of UC protocols. As Non-Interactive Public Verifiability is crucial when composing protocols with a distributed ledger, it can be beneficial when designing these with formal security in mind. We give a thorough discussion and formalization of what Non-interactive Public Verifiability means in the Universal Composability Framework and construct a general transformation that achieves this notion for a large class of cryptographic protocols. Our framework furthermore allows to reason about the composition of Non-Interactive Publicly Verifiable primitives.