Proxy signatures for delegating signing operation
CCS '96 Proceedings of the 3rd ACM conference on Computer and communications security
ICICS '97 Proceedings of the First International Conference on Information and Communication Security
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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.