Making Existing Quantum Position Verification Protocols Secure Against Arbitrary Transmission Loss
Rene Allerstorfer, Andreas Bluhm, Harry Buhrman, Matthias Christandl, Llorenç Escolà-Farràs, Florian Speelman, Philip Verduyn Lunel · Physical Review Letters · 2025
Signal loss threatens the security of quantum cryptography, especially in quantum position verification (QPV) protocols, where even small losses can compromise security. This Letter modifies traditional QPV to make high transmission loss between verifiers and the prover irrelevant for a class of protocols, including a practically interesting one based on BB84 states (QPV_{BB84}^{f}). Using photon presence detection and a small time delay, as well as a commitment before proceeding, the protocol's relevant loss rate is reduced to only that of the prover's lab, and the modified protocol has essentially the same security guarantees as the original one. The adapted protocol c-QPV_{BB84}^{f} thus offers strong security guarantees and feasibility over longer distances. We also discuss the practical implementation of the protocol and parameter estimates.