Cryptanalysis and Improvement of Das et al.'s Proxy Signature Scheme

In a proxy signature scheme, an original signer delegates his or her signing capability to a proxy signer, and then the proxy signer creates a signature on behalf of the original signer. Proxy signature schemes find applications in a variety of computing environments such as mobile agents for e-commerce, global distribution networks, mobile communications. Recently, Das et al. proposed a proxy signature scheme with effective revocation using bilinear pairings. In this paper, we point out two mistakes in their scheme. Further, we show that the scheme has still weaknesses even after eliminating those mistakes. Besides, we propose an improvement of their scheme to eliminate these weaknesses.