MAKING AN EMPTY PROMISE WITH A QUANTUM COMPUTER

Alice has made a decision in her mind. While she does not want to reve al it to Bob at this moment, she would like to convince Bob that she i s committed to this particular decision and that she cannot change it at a later time. Is there a way for Alice to get Bob's trust? Until re cently, researchers had believed that the above task can be performed with the help of quantum mechanics. And the security of the quantum sc heme lies on the uncertainty principle. Nevertheless, such optimism wa s recently shattered by Mayers and by us, who found that Alice can alw ays change her mind if she has a quantum computer. Here, we survey thi s dramatic development and its implications on the security of other q uantum cryptographic schemes.