UNCONDITIONALLY SECURE QUANTUM BIT COMMITMENT IS POSSIBLE

Bit commitment involves the submission of evidence from one party to another so that the evidence can be used to con rm a later revealed bit value by the rst party, while the second party cannot determine the bit value from the evidence alone. It is widely believed that unconditionally secure quantum bit commitment is impossible due to quantum entanglement cheating, which is codi ed in a general impossibility theorem. In this paper, the scope of this general impossibility proof is extended and analyzed, and gaps are found. Three speci c protocols are described for which the entanglement cheating as given in the impossibility proof fails to work. One of these protocols, QBC2, is proved to be unconditionally secure.