Upper Bound of Collective Attacks on Quantum Key Distribution

TL;DR

This paper establishes the theoretical maximum of Eve's information gain through collective attacks in various quantum key distribution protocols, showing their equivalence and potential for improved security proofs.

Contribution

It derives the capability limit of collective attacks in both entangled and non-entangled quantum key distribution protocols, highlighting their equivalence and security advantages.

Findings

Collective attacks are equally effective in entangled and non-entangled protocols.

Security proofs based on collective attacks can enhance tolerable error rates and key rates.

Theoretical limits of Eve's information extraction via collective attacks are established.

Abstract

Evaluating the theoretical limit of the amount of information Eve can steal from a quantum key distribution protocol under given conditions is one of the most important things that need to be done in security proof. In addition to source loopholes and detection loopholes, channel attacks are considered to be the main ways of information leakage, while collective attacks are considered to be the most powerful active channel attacks. Here we deduce in detail the capability limit of Eve's collective attack in non-entangled quantum key distribution, like BB84 and measurement-device-independent protocols, and entangled quantum key distribution, like device-independent protocol, in which collective attack is composed of quantum weak measurement and quantum unambiguous state discrimination detection. The theoretical results show that collective attacks are equivalent in entangled and non-entangled quantum key distribution protocols. We also find that compared with the security proof based on entanglement purification, the security proof based on collective attack not only improves the system's tolerable bit error rate, but also improves the key rate.