Loss-tolerant position-based quantum cryptography

TL;DR

This paper investigates the security of position-based quantum cryptography under realistic lossy conditions, demonstrating that certain protocols can tolerate significant channel loss with practical implementations.

Contribution

It introduces a loss-tolerant PBQC protocol using decoy states and analyzes its performance, showing improved loss tolerance in realistic scenarios.

Findings

Extended BB84-type PBQC protocol tolerates 13 dB loss with 1% error rate.

Continuous variable PBQC protocols are limited to 3 dB loss.

Decoy state method enhances practical security of PBQC.

Abstract

Position-based quantum cryptography (PBQC) allows a party to use its geographical location as its only credential to implement various cryptographic protocols. Such a protocol may lead to important applications in practice. Although it has been shown that any PBQC protocol is breakable if the adversaries pre-share an arbitrarily large entangled state, the security of PBQC in the bounded-quantum-storage model is still an open question. In this paper, we study the performance of various PBQC protocols over a lossy channel under the assumption that no entanglement is pre-shared between adversaries. By introducing the decoy state idea, we show that an extended BB84-type PBQC protocol implemented with a weak coherent source and realistic single photon detectors can tolerate an overall loss (including both the channel loss and the detection efficiency) of 13 dB if the intrinsic quantum bit error rate is 1%. We also study a few continuous variable PBQC protocols and show that they suffer from a 3 dB loss limitation.