= Ensemble-steering attack on quantum bit commitment
If the two honest <quantum state ensembles> have the same <density operator>, their independently prepared blocks are perfectly hiding. A dishonest sender can instead send one half of a <purification of a density operator> and retain the other. The <Hughston–Jozsa–Wootters theorem> allows a measurement of the retained system to prepare either honest ensemble after commitment. If verification checks only the declared states, either opening is then accepted with the honest probabilities. This gives a concrete failure of binding while preserving perfect hiding.
Back to article page
