Reply to recent scepticism about the foundations of quantum cryptography

TL;DR

This paper refutes recent claims that a fundamental flaw undermines quantum cryptography, clarifying that the skepticism is based on a misunderstanding of the criteria for secrecy.

Contribution

It clarifies misconceptions in recent critiques of quantum cryptography, reaffirming the robustness of its theoretical foundations.

Findings

Recent criticisms are based on a confusion between necessary and sufficient secrecy criteria

The claimed flaw does not invalidate existing security proofs in quantum cryptography

The paper defends the theoretical soundness of quantum cryptography

Abstract

In a series of recent papers, Hirota and Yuen claim to have identified a fundamental flaw in the theory underlying quantum cryptography, which would invalidate existing security proofs. In this short note, we sketch their argument and show that their conclusion is unjustified --- it originates from a confusion between necessary and sufficient criteria for secrecy.