Global ETD Search

11	Skupinové digitální podpisy / Group signature schemes Smrž, Jan January 2015 (has links) Digital signatures are widespread in IT nowadays. In some cases there is emphasized the security of signer identity when signing an electronic message. For this type of signature group digital signatures are suitable. In this thesis basic cryptographic functions are presented which are used for group digital signatures. The principle of group signatures is explained, its advantages and nowadays use. Further are explained electronic election and it dis- and advantages. The practical part is a design and implementation of system suitable for electronic election allowing anonymity of voters using group digital signatures.
12	Boneh-Boyen Signatures and the Strong Diffie-Hellman Problem Yoshida, Kayo January 2009 (has links) The Boneh-Boyen signature scheme is a short signature scheme which is provably secure in the standard model under the q-Strong Diffie-Hellman (SDH) assumption. The primary objective of this thesis is to examine the relationship between the Boneh-Boyen signature scheme and SDH. The secondary objective is to survey surrounding topics such as the generic group model, related signature schemes, intractability assumptions, and the relationship to identity-based encryption (IBE) schemes. Along these lines, we analyze the plausibility of the SDH assumption using the generic bilinear group model. We present the security proofs for the Boneh-Boyen signature scheme, with the addition of a small improvement in one of the probability bounds. Our main contribution is to give the reduction in the reverse direction; that is, to show that if the SDH problem can be solved then the Boneh-Boyen signature scheme can be forged. This contribution represents the first known proof of equivalence between the SDH problem and Boneh-Boyen signatures. We also discuss the algorithm of Cheon for solving the SDH problem. We analyze the implications of Cheon's algorithm for the security of the Boneh-Boyen signature scheme, accompanied by a brief discussion on how to counter the attack. cryptography digital signatures signature scheme Diffie-Hellman Strong Diffie-Hellman SDH Boneh-Boyen signatures Pollard rho Pollard lambda baby-step giant-step assumptions short signatures random oracle generic group BLS Waters Okamoto identity-based encryption IBE Cheon's algorithm partial fraction security existential forgery Combinatorics and Optimization
13	Boneh-Boyen Signatures and the Strong Diffie-Hellman Problem Yoshida, Kayo January 2009 (has links) The Boneh-Boyen signature scheme is a short signature scheme which is provably secure in the standard model under the q-Strong Diffie-Hellman (SDH) assumption. The primary objective of this thesis is to examine the relationship between the Boneh-Boyen signature scheme and SDH. The secondary objective is to survey surrounding topics such as the generic group model, related signature schemes, intractability assumptions, and the relationship to identity-based encryption (IBE) schemes. Along these lines, we analyze the plausibility of the SDH assumption using the generic bilinear group model. We present the security proofs for the Boneh-Boyen signature scheme, with the addition of a small improvement in one of the probability bounds. Our main contribution is to give the reduction in the reverse direction; that is, to show that if the SDH problem can be solved then the Boneh-Boyen signature scheme can be forged. This contribution represents the first known proof of equivalence between the SDH problem and Boneh-Boyen signatures. We also discuss the algorithm of Cheon for solving the SDH problem. We analyze the implications of Cheon's algorithm for the security of the Boneh-Boyen signature scheme, accompanied by a brief discussion on how to counter the attack. cryptography digital signatures signature scheme Diffie-Hellman Strong Diffie-Hellman SDH Boneh-Boyen signatures Pollard rho Pollard lambda baby-step giant-step assumptions short signatures random oracle generic group BLS Waters Okamoto identity-based encryption IBE Cheon's algorithm partial fraction security existential forgery Combinatorics and Optimization

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