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Title: Certificateless signature and time capsule signature : secure, efficient and usable digital signature schemes
Other Titles: Wu zheng shu qian ming ji shi jian jiao nang qian ming : an quan, gao xiao, shi yong de shu zi qian ming
無證書簽名及時間膠囊簽名 : 安全, 高效, 實用的數字簽名
Authors: Hu, Chunyan (胡春燕)
Department: Dept. of Computer Science
Degree: Master of Philosophy
Issue Date: 2007
Publisher: City University of Hong Kong
Subjects: Computer security
Digital signatures
Notes: CityU Call Number: QA76.9.A25 H79 2007
Includes bibliographical references (leaves 97-106)
Thesis (M.Phil.)--City University of Hong Kong, 2007
viii, 106 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: Internet boom brings along the prevalence of E-commerce, whose `monetary' nature places signi¯cant demands on user authentication and message integrity. As a fundamental building block of the Public Key Infrastructure (PKI), digital signature is a mechanism for authenticating the integrity of messages and the identity of the signer. Involving a secret key for signature generation and a public key for veri¯cation, a digital signature has the properties of non- repudiation as well as public veri¯ability. Therefore, the security of digital signatures relies heavily on the privacy of secret keys and the authenticity of public keys. Accordingly, key management plays an essential role in digital signature framework. Its management cost and security level is quite crucial on evaluating e±ciency and e®ectiveness of a digital signature system. Conventional digital signature scheme requires high cost to manage certi¯- cates, which are used to bind public keys with user identities. In identity-based signature, user identity is adopted as its public key, thus, no certi¯cate is in- volved. However, key escrow becomes an inherent problem, since all the secret keys are generated by Key Generation Center (KGC). As an advanced alter- native, certi¯cateless signature borrows nice features from conventional digital signature and identity-based signature. It eliminates the use of certi¯cates, and circumvents the key escrow problem. Since the concept of certi¯cateless signature was ¯rst introduced in 2003, a lot of e®orts were paid afterwards to search for security model and generic constructions. Although certi¯cateless signature is derived from conventional signature and identity-based signature, its security model is more complicated than intuitive combination of two antecessors without any adjustment. In- volving more communication parties, carving up the boundary of each one's responsibility and knowledge power becomes crucial. In our study of certi¯cateless signature, we ¯rst categorize the two types of attacks against a certi¯cateless public key cryptosystem, namely KGC Attack and Key Replacement Attack. Based on that, we simplify previous de¯nition of certi¯cateless signature, and introduce a new security model, which is more versatile to capture various attacks compared with previous ones. After that, we examine Yum and Lee's ACISP 2004 paper, and ¯x their security leak by providing an improved generic construction. Certi¯cateless signature improves the security and e±ciency of existing digital signature topology in general purposes. However, for some E-commerce applications, speci¯c system requirements should be considered. In a set of business products including e-ticket, e-check, and e-bid, `future' is an imbedded feature. A signature should be modelled to bear a (future) time t so that it will only be valid at time t or later. This feature is captured in a concept named Time Capsule Signature (TC-Sign). Time Capsule Signature was well modelled by Dodis and Yum in 2005. To further enhance its usability and reduce construction cost, we propose an alternative security model and new constructions based on practical demands. Readers will ¯nd our incessant e®orts on improving security, e±ciency and usability of digital signature schemes throughout this thesis.
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