Paper 2012/288

Fair Exchange of Short Signatures without Trusted Third Party

Philippe Camacho

Abstract

We propose a protocol to exchange Boneh-Boyen short signatures in a fair way, without relying on a trusted third party. Our protocol is quite practical and is the first of the sort to the best of our knowledge. Our construction uses a new non-interactive zero-knowledge (NIZK) argument to prove that a commitment is the encryption of a bit vector. We also design a NIZK argument to prove that a commitment toa bit vector $v=(b_1,b_2,...,b_\secparam)$ is such that $\sum_{i \in [\secparam]}b_i2^{i-1}=\Blinding$ where $\Blinding$ is the discrete logarithm of some public value $D=g^\Blinding$. These arguments may be of independent interest.