Comments on a Threshold Proxy Signature Scheme Based on the RSA Cryptosystem

In a (t, n) proxy signature scheme, the original signer can delegate his/her signing capability to n proxy signers such that any t or more proxy singers can sign messages on behalf of the former, but t − 1 or less of them cannot do the same thing. Such schemes have been suggested for use in a number of applications, particularly in distributed computing where delegation of rights is quite common. Based on the RSA cryptosystem, Hwang et al. recently proposed an efficient (t, n) threshold proxy signature scheme. In this paper we identify several security weaknesses in their scheme and show that their scheme is insecure.