Attack on Kang et al.'s Identity-Based Strong Designated Verifier Signature Scheme

In this paper, we present a universal forgery attack on Kang et al.’s identity-based strong designated verifier signature (IBSDVS) scheme. We show anyone can forge a valid IBSDVS on an arbitrary message without the knowledge of the private key of either the signer or the designated verifier. Moreover, we point out that Kang et al.’s scheme does not satisfy the properties of strongness and nondelegatability. At last, an improved IBSDVS scheme for Kang et al.’s scheme is presented, and it is provably secure and achieves all the requirements for an IBSDVS.