Forgery Attack on Two ID-Based Proxy Signature Schemes from Bilinear Pairings

Since Mambo et al. introduced the concept of proxy signature in 1996, many proxy signature schemes have been proposed. Recently, Wang et al. and Zhao et al. proposed an ID-based proxy signature scheme and an ID-based anonymous proxy signature scheme, respectively. And they also claimed that the proposed scheme satisfied the required security properties of proxy signature. In this paper, we show that these two proxy signature schemes are insecure against original signer´s forgery, and can not provide undeniability.