Quantum Secure Key Exchange with Position-based Credentials

Abstract: Quantum key distribution (QKD) provides an information-theoretic way of securely exchanging secret keys, and typically relies on pre-shared keys or public keys for message authentication. To lift the requirement of pre-shared or public keys, Buhrman et. al. [SIAM J. Comput. 43, 150 (2014)] proposed utilizing the location of a party as a credential. Here, we extend upon the proposal, develop a QKD protocol with location credentials using quantum position verification (QPV) based message and identity authentication. By using QKD with delayed authentication as a base, and later simplifying QPV-based message authentication, we significantly reduce the number of QPV runs, which currently acts as a bottleneck. Besides demonstrating security for the proposed protocol, we also provide improvements to QPV security analysis, including generalization of the QPV adversary model, tightening a trace distance bound using semidefinite programming, and propose a multi-basis QPV requiring only BB84 state preparation but with multiple measurement basis.