Security of "Counterfactual Quantum Cryptography"

TL;DR

This paper analyzes the security of a counterfactual quantum key distribution protocol, establishing its equivalence to an entanglement distillation protocol and providing a rigorous security proof and key rate analysis.

Contribution

It demonstrates the protocol's security through equivalence to EDP, offering a formal security proof and insights into factors affecting security.

Findings

Protocol is equivalent to an entanglement distillation protocol

Security proof is established with perfect single photon source

Security depends on bit error rate and photon yields

Abstract

Recently, a "counterfactual" quantum key distribution scheme was proposed by Tae-Gon Noh [1]. In this scheme, two legitimate distant peers may share secret keys even when the information carriers are not traveled in the quantum channel. We find that this protocol is equivalent to an entanglement distillation protocol (EDP). According to this equivalence, a strict security proof and the asymptotic key bit rate are both obtained when perfect single photon source is applied and Trojan-horse attack can be detected. We also find that the security of this scheme is deeply related with not only the bit error rate but also the yields of photons. And our security proof may shed light on security of other two-way protocols.