Security of quantum key distribution from generalised entropy accumulation

TL;DR

This paper introduces a formal framework for quantum key distribution security analysis, demonstrating that security against general attacks can be reduced to security against collective attacks through a numerical approach, using generalized entropy accumulation.

Contribution

It provides a new formal framework that simplifies security proofs for QKD protocols by reducing general attack security to collective attack security via entropy accumulation.

Findings

Security against general attacks reduces to collective attacks.

Security analysis can be performed through numerical computation.

Framework applies directly to prepare-and-measure protocols.

Abstract

The goal of quantum key distribution (QKD) is to establish a secure key between two parties connected by an insecure quantum channel. To use a QKD protocol in practice, one has to prove that a finite size key is secure against general attacks: no matter the adversary's attack, they cannot gain useful information about the key. A much simpler task is to prove security against collective attacks, where the adversary is assumed to behave identically and independently in each round. In this work, we provide a formal framework for general QKD protocols and show that for any protocol that can be expressed in this framework, security against general attacks reduces to security against collective attacks, which in turn reduces to a numerical computation. Our proof relies on a recently developed information-theoretic tool called generalised entropy accumulation and can handle generic prepare-and-measure protocols directly without switching to an entanglement-based version.