Cryptanalysis of Lin et al\u27s efficient strong designated verifier proxy signature scheme for electronic commerce

Strong Designated Verifier Proxy Signature (SDVPS) Scheme is the combination of the proxy signature scheme and the designated verifier signature scheme. An SDVPS scheme enables the proxy signer, on behalf of the original signer, to sign a message. A designated verifier can only check the validity of the signature. Lin et al. proved that their scheme is resistant against existential forgery under adaptive chosen-message attacks (EF-CMA), Lin et al. (2012). However, Zhou showed in Attacks on a Strong Designated Verifier Proxy Signature Scheme , Zhou (2014a) that their scheme was insecure by giving four attacks and Zhou proposed an improvement on their scheme which he wrote in his paper Improvement on Lin et als Strong Designated Verifier Proxy Signature Scheme for Electronic Commerce, Zhou (2014b). In this paper, we show that the scheme can be forged by using Zhou\u27s four attacks and our own contributed two attacks. Furthermore, we proposed an improvement for the scheme. Analysis shows that the improvement was resistant against the given six attacks