Improvement of a forward-secure proxy signature scheme

We point out some shortcomings of a proxy signature scheme which was proposed by Wang et al. and propose an improved scheme. In the improved scheme, the proxy key is produced by original signer and proxy signer, the key evolution algorithm takes use of a secure hash function, and the key updates after each signature, so it can limit the number of signatures and save the computation, so the new scheme is strong forward-secure and more efficient. Its security is based on the discrete logarithm problem.