Security Analysis of a Threshold Proxy Signature Scheme

The t-out-of-n threshold proxy signatures allow an original signer to delegate his signing capability to a group of proxy signers, and t or more proxy signers can generate valid signatures by cooperating. Recently, Liu and Huang proposed a variant of threshold proxy signature scheme in which all proxy signers remain anonymous. The authors claimed their construction satisfies unforgeability, proxy signer’s deviation, identifiability, undeniability and verifiability. In this paper, however, we show that their scheme does not provide the proxy signer’s deviation and identifiability requirements. Keyword : proxy signature, threshold proxy signature, anonymous, proxy signer’s deviation, identifiability