A modified (t, n) threshold proxy signature scheme based on the RSA cryptosystem

Recently, a threshold proxy signature scheme based on RSA cryptosystem to enhance the flexibility of traditional proxy signature scheme has been proposed by Hwang et al. However this new threshold proxy signature scheme is still unworkable because there is some security weakness, such as the similar to RSA reblocking problem and each proxy signer can not find out the Lagrange coefficient, exist in this new scheme. In this paper we not only give some security flaws to show that their scheme is insecure but also provide a feasible scheme to solve the open problem.