Information-theoretically and computationally secure key agreement in cryptography

Mitsugu Iwamoto, Kazuo Ohta, Junji Shikata

This paper analyzes the formalizations of information-theoretic security for the fundamental primitives in cryptography: symmetric-key encryption and key agreement. Revisiting the previous results, we can formalize information-theoretic security using different methods, by extending Shannon's perfect secrecy, by information-theoretic analogues of indistinguishability and semantic security, and by the frameworks for composability of protocols. We show the relationships among the security formalizations and obtain the following results. First, in the case of encryption, there are significant gaps among the formalizations, and a certain type of relaxed perfect secrecy or a variant of information-theoretic indistinguishability is the strongest notion. Second, in the case of key agreement, there are significant gaps among the formalizations, and a certain type of relaxed perfect secrecy is the strongest notion. In particular, in both encryption and key agreement, the formalization of composable security is not stronger than any other formalizations. Furthermore, as an application of the relationships in encryption and key agreement, we simultaneously derive a family of lower bounds on the size of secret keys and security quantities required under the above formalizations, which also implies the importance and usefulness of the relationships.

Ueli M. Maurer, Stefan Wolf

Xiaolei Dong

In the area of network information security,key agreement is essential between servers and clients.To overcome the key escrow property of identity-based cryptography,proposed certificateless public key cryptography,it combined the advantages of the traditional PKI and the identity-based cryptography.This paper proposed a new certificateless two-party key agreement protocol using pairing operation in elliptic curves,it only required each party to compute one pairing.Proved its security in ECK(extended Canetti-Krawczyk) model.Compared with existing certificateless protocols,the newly proposed key agreement protocol has better security and efficiency.

Ueli M. Maurer

Wenhao Liu, Chunxiang Xu, Jian Feng Xu

Certificateless cryptography aims at combining the advantages of identity based and public key cryptography in order to avoid the key escrow problem inherent in the identity based cryptography and cumbersome certificate management in the traditional public key infrastructure. The provably secure certificateless key agreement protocol is proposed by Lippold et al. in 2009, but their protocol suffers from computation burden. Owing to the above-mentioned situations, a new certificateless two party key agreement protocol (CL-KA) is proposed and the security attributes are analyzed in the extended Canetti-Krawzcyk(eCK) security model. Our protocol only requires each entity to compute two pairings, up to now, it turns out to be the most efficient one of all the previously known security CL-KA schemes.

Ueli M. Maurer