Abstract

We show that all proposed quantum bit commitment schemes are insecure because the sender can always cheat successfully by using an EPR-type of attack and delaying her measurement until she opens her commitment. PACS Numbers: 03.65.Bz, 89.70.+c, 89.80.+h Typeset using REVT E X e-mail: hkl@sns.ias.edu y e-mail: chau@sns.ias.edu A bit commitment scheme generally involves two parties, a sender, Alice and a receiver, Bob. Suppose that Alice has a bit (b = 0 or 1) in mind, to which she would like to be committed towards Bob. That is to say, she wishes to provide Bob with a piece of evidence that she has a bit in mind and that she cannot change it. Meanwhile, Bob should not be able to tell from that evidence what b is. At a later time, however, it must be possible for Alice to open the commitment. In other words, Alice must be able to show Bob which bit she has committed to and convinced him that this is indeed the genuine bit that she had in mind when she committed. Various quantum bit...

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