Universal composable security of multi-signature schemes

Zecheng Wang

Zhibin Li

Since up to now the security of multi-signature protocols has only been considered in a single instance, the security of a multi-signature protocol when it is running with many other protocols concurrently was studied in the universal composable security framework. Firstly, the idea functionality of a multi-signature protocol was defined formally. Then, based on Waters' signature scheme, a multi-signature protocol was presented, which was proved to be Unified Communications (UC) secure. Thus, the presented multi-signature protocol can run safely in multi-protocol executing environments, such as Internet.

Malone-Lee, John C, Dent, AW

ZHAO Chen,YU Huifang,LI Jianmin

At present,most group signature is only secure in the standard alone.Its security becomes weak in multiple protocol environment.In view of this,the security of group signature protocol is studied in the multiple concurrent execution under the universally composable framework.Since the protocol can be analyzed modularly under the universally composable framework,an ideal function of group signature protocol is defined in this framework.Then a group signature protocol is proposed to realize the ideal function,and its universally composable security as well as unforgeability is also proved.Furthermore,a concrete instance of this universally composable group signature protocol is given.Analysis results show that this protocol security is suitable for applications in multiple concurrent environment.

Ran Canetti, Asaf Cohen, Yehuda Lindell

Dominique Unruh

A protocol has everlasting security if it is secure against adversaries that are computationally unlimited after the protocol execution. This models the fact that we cannot predict which cryptographic schemes will be broken, say, several decades after the protocol execution. In classical cryptography, everlasting security is difficult to achieve: even using trusted setup like common reference strings or signature cards, many tasks such as secure communication and oblivious transfer cannot be achieved with everlasting security. An analogous result in the quantum setting excludes protocols based on common reference strings, but not protocols using a signature card. We define a variant of the Universal Composability framework, everlasting quantum-UC, and show that in this model, we can implement secure communication and general multi-party computation using signature cards as trusted setup.