On the Security of Two Pairing-Based Signature Schemes

Digital signatures have uncountable applications in our everyday life. They provide authentication, integrity and non-repudiation. Pairing-based cryptography with its special features and properties has given rise not only to ceritiface- free (e.g. identity-based and certificateless) cryptography but also to the development of many efficient signature schemes. In 2013, Sharma Sahu and Sharma proposed a pairing-based based signature scheme which was derived from the identification scheme proposed by Popescu. Certificateless cryptography was proposed with the aim of bridging between traditional public key cryptography and identity-based cryptography. Zhang et al. proposed an efficient certificateless signature scheme and claimed that their proposed scheme is better than all the existing schemes in the literature in terms of efficiency. In this paper, we mount a total break attack on Sharma et al.´s scheme and show that Zhang et al.´s certificateless scheme is not secure by mounting a universal forgery attack on their scheme.