Defeating Classical Bit Commitments With a Quantum Computer

It has been recently shown by Mayers that no bit commitment is secure if the participants have unlimited computational power and technology. However it was noticed that a secure protocol could be obtained by forcing the cheater to execute a measurement. Similar situations had been encountered previously in the design of Quantum Oblivious Transfer. The question is whether a classical bit commitment could be used for this specific purpose. We demonstrate that, surprisingly, classical unconditionally concealing bit commitments do not help. 1 Introduction After that Mayers obtained his general impossibility theorem for bit commitment (see the Appendix of [13] and [1, 2]), different kind of ideas were proposed by some of us with the hope to realize unconditionally secure bit commitment. It was then realized that these apparently promising ideas were also ruled out by Mayers' attack. These attempts contributed to enhance our understanding of what is going on with quantum bit commitment.Howe..