A Modified and Practical Threshold Proxy Signature Scheme Based on RSA

Wen et al. recently showed Hwang´s threshold proxy signature scheme based on RSA has some mistakes of equation and which makes it unsecured. So they modified Hwang´s scheme. However, we find the core of the problem of the value of Lagrange coefficient is still not solved and the right of proxy signature combiner isn´t defined clearly in the modified scheme. We modify Hwang´s scheme once more and our modified scheme needn´t compute the inverse when we compute the value of the Lagrange coefficient. Furthermore, in our modified scheme proxy signature combiner don´t know the Euler function value Phi(N₀) which can prevent combiner and partial signer from the conspiracy attack. The improvement makes the scheme perfect and practical.