| Summary: | 博士 === 國立交通大學 === 資訊管理所 === 91 === Digital signature is one of the main issues in modern cryptographic research. As hand-written signatures and seals do in real life, digital signature provides the functions of endorsement and authorization in the digitalized world of computers and networks. In terms of security services, digital signature achieves message integrity, signer authenticity, and signature undeniability.
Under certain circumstances, a signer may not be able to effectively perform his private “signing power”, and has to authorize a proper delegate to sign messages on behalf of him. In this thesis, how to perform such “signature delegation” with a “group-oriented” manner is researched. Two issues are considered herein: how a signer, namely the “authority”, authorizes his signing power to a delegation group; and, how members in the delegation group cooperate to generate valid digital signatures, namely delegated signatures. Regarding all possible scenarios for group-oriented signature delegation, four system models are defined:
〈Loose-authorization model〉The authority chooses a delegation group and allows each group member to independently generate valid delegated signatures.
〈Strict-authorization model〉The authority chooses a delegation group and demands that all group members have to cooperate for generating valid delegated signatures.
〈Threshold-authorization model〉The authority chooses a delegation group of n members and defines a threshold value t < n. Then, any subgroup consisting of t or more group members can generate valid delegated signatures.
〈Generalized-authorization model〉The authority chooses a delegation group and defines qualified subgroups. Then, valid delegated signatures can only be generated via the cooperation of all members from any of the predefined qualified subgroups.
In accordance with these system models, five authorization conditions and four security requirements are defined. Then, four concrete schemes are proposed to respectively realize these models. The proposed schemes are based on bilinear pairings and designated for the identity-based public key cryptosystem. Due to the bilinear pairings, the proposed schemes are simple in construction and efficient in performance. Moreover, all schemes are derived from the same basic identity-based signature scheme, and as a result constitute a systematic solution for group-oriented signature delegation.
|
|---|
