Security bound of cheat sensitive quantum bit commitment

TL;DR

This paper analyzes cheat sensitive quantum bit commitment protocols, showing inherent security limitations where both parties can cheat with significant probability, and finds that optimal protocols are trivial and practically useless.

Contribution

It identifies common features in CSQBC protocols that allow significant cheating, demonstrating the limitations and triviality of optimal cheat sensitive protocols.

Findings

Receiver can learn substantial information before unveiling

Cheating success probability is at least 50% for both parties

Optimal protocols are trivial and offer little practical security

Abstract

Cheat sensitive quantum bit commitment (CSQBC) loosens the security requirement of quantum bit commitment (QBC), so that the existing impossibility proofs of unconditionally secure QBC can be evaded. But here we analyze the common features in all existing CSQBC protocols, and show that in any CSQBC having these features, the receiver can always learn a non-trivial amount of information on the sender's committed bit before it is unveiled, while his cheating can pass the security check with a probability not less than 50%. The sender's cheating is also studied. The optimal CSQBC protocols that can minimize the sum of the cheating probabilities of both parties are found to be trivial, as they are practically useless. We also discuss the possibility of building a fair protocol in which both parties can cheat with equal probabilities.