A study on security and efficiency of cryptographic protocols

幸一 櫻井

Aggelos Kiayias, Hong-Sheng Zhou

We study efficient protocol constructions against adaptive corruption in the universal composition framework. For standard cryptographic tasks, we propose a new framework to design efficiently two-party secure function evaluation protocols, and then apply it to oblivious transfer and obtain the first practical such constructions. Regarding reactive cryptographic tasks, we present a framework for designing blind signatures, and construct the first practical protocols for this task. ^

Oana Ciobotaru, Dominique Unruh, Michael Backes A

Long-term security ensures that a protocol remains secure even in the future, when the adversarial computational power could, potentially, become unlimited. The notion of universal composability preserves the security of a cryptographic protocol when it is used in combination with any other protocols, in possibly complex systems. The area of long-term universally composable secure protocols has been developed mostly by Müller-Quade and Unruh. Their research conducted so far has shown the existence of secure long-term UC commitments under general cryptographic assumptions, thus without having an emphasis on the efficiency of the protocols designed. Building on their work and using very efficient zero-knowledge proofs of knowledge from [CL02], this thesis presents a new long-term universally composable secure commitment protocol that is both efficient and plausible to use in practice.

Bartosz Przydatek

Richard J. Berger, Sampath Kannan, René Peralta

Meiran Galis, Tomislav Unkašević, Zoran Banjac +1 more

Introduction/purpose: The problem of efficient distribution of cryptographic keys in communication systems has existed since its first days and is especially emphasized by the emergence of mass communication systems. Defining and implementing efficient protocols for symmetric cryptographic keys establishment in such circumstances is of great importance in raising information security in cyberspace. Methods: Using the methods of Information Theory and Secure Multiparty Computation, protocols for direct establishment of cryptographic keys between communication parties have been defined. Results: The paper defines two new approaches to the problem of establishing cryptographic keys. The novelty in the protocol defined in the security model based on information theory is based on the source of common randomness, which in this case is the EEG signal of each subject participating in the communication system. Experimental results show that the amount of information leaking to the attacker is close to zero. A novelty in the second case, which provides security with keys at the level of computer security by applying Secure Multiparty Computation, is in the new application field, namely generation and distribution of symmetric cryptographic keys. It is characteristic of both approaches that within the framework of formal theories, it is possible to draw conclusions about their security characteristics in a formal way. Conclusions: The paper describes two new approaches for establishing cryptographic keys in symmetric cryptographic systems with experimental results. The significance of the proposed solutions lies in the fact that they enable the establishment of secure communication between communication parties from end to end, avoiding the influence of a trusted third party. In that way, the achieved communication level security significantly increases in relation to classical cryptographic systems.