| Summary: | 碩士 === 朝陽科技大學 === 資訊管理系碩士班 === 93 === In current proxy signature schemes, an original signer delegates her/his signing capability to a proxy signer, and then the proxy signer can sign messages on behalf of the original signer. Although these schemes have succeeded in proxy delegations, they share a common problem. That is, a verifier cannot ascertain a proxy signature was signed by the proxy signer during the delegation period. Additionally, these schemes are in general defective in proxy revocations. In this research, we proposed two new proxy signature schemes to resolve the above problems. The first scheme utilizes a trusted third party called authentication server to ensure that proxy signatures can only be generated during valid delegation period. Also, the original signer can revoke her delegation whenever she wants. In the first scheme, it is required that the authentication server has to be trusted unconditionally. To alleviate the trust level, the other proposed scheme employs the time-stamping service and Pedersen''s
threshold cryptosystem. It is shown in the thesis that both schemes are secure and resolve the stated problems. The performance of both schemes are also analyzed.
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