| Summary: | 碩士 === 國立高雄應用科技大學 === 資訊工程系 === 104 === Proxy signature schemes allow a signer to designate another party as a proxy signer. The proxy signer can sign a document on behalf of the original signer, while she /he is away (on vacation for example). Identity-Based cryptography uses a per-son's ID as public key to avoid the need of certificate. Recently, more and more Iden-tity-Based Proxy Signature (IBPS) schemes have been proposed. In particular, Hu et al. proposed an IBPS scheme in 2015, and showed that their scheme is more efficient than two other IBPS schemes proposed by Cao et al. and Gu et al., respectively.
Although Hu et al.'s scheme is efficient, they did not give or cite a formal security definition. In this paper, we adopt the formal definition of proxy signature scheme given by Xu et al. in 2005, and point out that Hu et al.'s scheme is insecure according to this definition. In particular, if the original signer gets the proxy signer's standard signature on a specific message, the original signer can forge the proxy signature on any message. In other words, the original signer can produce the proxy signature on his/her own (without the proxy singer), and later claims that this signature was signed by the proxy signer. We propose a scheme to fix this problem. Our scheme is slightly less efficient than Hu et al.'s scheme, but is more efficient than Cao et al.'s and Gu et al.'s schemes.
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