Quantum key distribution based on orthogonal states allows secure quantum bit commitment

For more than a decade, it was believed that unconditionally secure quantum bit commitment (QBC) is impossible. But basing on a previously proposed quantum key distribution scheme using orthogonal states, here we build a QBC protocol in which the density matrices of the quantum states encoding the commitment do not satisfy a crucial condition on which the no-go proofs of QBC are based. Thus the no-go proofs could be evaded. Our protocol is fault-tolerant and very feasible with currently available technology. It reopens the venue for other "post-cold-war" multi-party cryptographic protocols, e.g., quantum bit string commitment and quantum strong coin tossing with an arbitrarily small bias. This result also has a strong influence on the Clifton-Bub-Halvorson theorem which suggests that quantum theory could be characterized in terms of information-theoretic constraints.Comment: Published version plus an appendix showing how to defeat the counterfactual attack, more references [76,77,90,118-120] cited, and other minor change

Quantum Bit-Commitment for Small Storage Based on Quantum One-Way Permutations (Extended Abstract)

Toshiyuki Isshiki Keisuke Tanaka Department of Mathematical and Computing Sciences, Tokyo Institute of Technology, 1-12-1 Ookayama Meguro-ku, Tokyo 152-8552, Japan { isshiki9, keisuke} @is.titech.ac.jp Abstract We propose quantum bit-commitment schemes based on quantum one-way permutations. Our schemes reduces the number of bits which Bob needs to store until the opening phase compared with the classical counterpart. Keywords Bit-commitment, Quantum computation, One-way permutation.