Security Analysis and Improvement of a (t, n) Threshold Proxy Signature Scheme

Recently, H. Jiang proposed a (t, n) threshold proxy sig nature scheme based on RSA cryptosystem, in which any t or more proxy signers can cooperatively generate a proxy signature while t-1 or less of them can´t do it. In this paper, we propose a security analysis of H. Jiang´s threshold proxy signature scheme and show that when e>p+q, the original signer can compute the group proxy private key d and then generate any valid proxy signature. Therefore, this scheme doesn ´t satisfy the security properties of threshold proxy signatures when e>p+q. Fortunately, this security weakness can be easily repaired.