The Analysis of an Efficient and Provably Secure ID-Based Threshold Signcryption Scheme and Its Secure Version

Abstract

In this paper,we analyze an identity-based threshold signcryption (IDTSC)scheme proposed in ICCCAS'2008, although Li and Yu pointed out that the scheme is the first provably secure scheme which is secure against adaptive chosen ciphertext attacks and secure in the sense of unforgeability, we show that the signcryption in the scheme is easily forged by the appointed clerk who is one of the members , the clerk can impersonate the members to forge valid signcryption to any receiver, then we give a secure version which we prove its confidentiality under the Decisional Bilinear Diffie-Hellman assumption and its unforgeability under the Computational Diffie-Hellman assumption in the random oracle model. Scheme turns out to be more efficient than the previously proposed schemes.