Cryptanalysis and Improvement of a Constant-Size Identity Based Ring Signature Scheme

Ring signature is of vital importance to secure electronic voting. Many ID-based ring signature schemes have been put forward, but most of them are not constant-size. Au etc proposed a constant-size ID-based ring signature without random oracles. The size of the signature is independent of the size of the ring. In stronger security model, the constant-size ID-based ring signature scheme can be forged. A forged method was presented in this paper. In order to resist this attack, we improve the original ring signature scheme. The improved scheme is secure even in the stronger security model.