Improvement of Hsu-Wu-He’s Proxy Multi-signature Schemes

Abstract

In 2005, for reducing Yi et al.’s proxy multi-signature schemes in terms of computational complexity and communication cost, Hsu, Wu and He proposed new proxy multi-signature schemes. Unfortunately, with this paper, we will show that their schemes are insecure, because any malicious attacker can alone forge valid proxy multi-signatures for any message to impersonate an original signer (or a proxy signer) by choosing proper public key as long as he has obtained some users’ public keys. We further improve their schemes to eliminate the security flaw of Hsu-Wu-He’s schemes. Moreover, the im-provements still maintain the advantages of their schemes while reducing the computational complexity.