Forward secure designated-verifier proxy signature scheme

As the existing designated-verifier proxy signature can not provide forward-security,so a forward secure designated-verifier proxy signature scheme was proposed by applying the concept of forward security to the designated-verifier proxy signature,based on the difficulty of solving discrete logarithm problems and the strong RSA assumption.In the scheme,proxy signature is forward secure,even if an adversary has gotten the current proxy signers' key,it could not forge proxy signature pertaining to the past,that is,previous generated proxy signature still remains valid.