Security in the Bounded Quantum Storage Model (iCIS seminar) - Juerg Wullschleger

Due to a famous result by Mayers, and Lo and Chau, it is impossible to achieve bit commitment and oblivious transfer in an unconditionally secure way, even in the quantum setting. Damgaard et al. showed how to securely implement bit commitment and oblivious transfer in the bounded quantum storage model, where the adversary is only allowed to store a limited number of qubits. First, we review their protocols and security definitions and show that they are not strong enough to imply composability. We will present a security framework for the bounded quantum storage model, and show that our definitions imply that protocols can be composed sequentially. We show how the protocol for oblivious transfer and the proof of its security need to be changed in order to achieve a secure implementation in our model. Since our definitions are composable, a secure implementation of bit commitment follows easily by a reduction to oblivious transfer. This is joint work with Stephanie Wehner.