It has been recently shown by Mayers that no bit commitment scheme 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 perform 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.Comment: 13 pages. Supersedes quant-ph/971202
