Cryptography in the Bounded Quantum-Storage Model

Most of todays cryptography relies on the assumption that a potential attacker cannot solve some computational problem (e.g. factor a large integer). It has been shown in the early 80's that with the use of quantum-mechanical effects, certain cryptographic tasks can be done unconditionally, i.e., secure against computationally unbounded attackers: Quantum-cryptography, and with it the hope that (m)any cryptographic task(s) can be solved this way, was born. This hope was smashed in the late 90's, when it was shown that any non-trivial cryptographic task involving two mutually distrusted parties cannot be done unconditionally by means of quantum-cryptography.<br/> We propose a new approach to circumvent this impossibility result. We construct quantum-cryptographic schemes which are secure under the sole assumption that the attacker's quantum memory is limited. This is motivated by the fact that storing even a single qubit for more than a fraction of a second seems to be out of reach with today's technology. This approach allows for practical schemes for Oblivious Transfer and for Bit Commitment.<br/> (Joint work with Ivan Damgård, Louis Salvail and Christian Schaffner)