Improvement of a Proxy Multi-Signature Scheme Without Random Oracles

A proxy multi-signature scheme permits two or more original singers to delegate their signing powers to the same proxy signer. Recently, Liu et al. proposed the first proxy multi-signature that be proven secure in the standard model, which can be viewed as a two-level hierarchical signature due to Waters. However, because of the direct employment of Waters' signature, their scheme needs a relatively large number of public parameters and is not tightly reduced to the security assumption. In this paper, inspired by Boneh, Boyen's technique and Waters' technique, the authors propose a new proxy multi-signature scheme without random oracles, whose unforgeability can be tightly reduced to the CDH assumption in bilinear groups.