Comment on "Security Proof for Cryptographic Protocols Based Only on Monogamy of Bell's Inequality Violations"

TL;DR

This paper critically examines a recent security proof for quantum key distribution based solely on Bell inequality monogamy, highlighting an unjustified assumption about the eavesdropper's measurement outcomes and providing a counter-example.

Contribution

It identifies a flaw in a prior security proof by challenging the assumption that the eavesdropper's outcome is binary, offering a counter-example to demonstrate the issue.

Findings

The previous proof's assumption is unjustified.

A counter-example invalidates the security claim.

The security proof needs revision to account for more general eavesdropper models.

Abstract

Recently, Pawlowski [Phys. Rev. A 82, 032313 (2010)] claimed to have proven the security of a quantum key distribution by using only the monogamy of Bell's inequality violations. In the proof, however, he tacitly assumed that the eavesdropper's outcome is binary. The assumption cannot be justified because Eve's (eavesdropper's) power can only be limited by natural principle. We provide a counter-example for a step of the proof.