Cryptanalysis and Improvement of Two Blind Proxy Signature Schemes

Cryptanalysis of two blind proxy signatures is made, which shows that neither of them satisfy unforgeability of proxy signature. Corresponding forgery attack is presented. Using the forgery attack, a dishonest original signer can forge the proxy key and generate valid blind proxy signatures. According to security drawback of the two existed signature schemes, two improved blind proxy signature scheme are proposed. Security analysis shows that these two improved schemes can resist the original signerpsilas forgery attack and also satisfy other properties of blind proxy signature scheme.