Position-Based Quantum Cryptography: Impossibility and Constructions
The aim of position-based cryptography is to use the geographical position of a party as its only credential. In this paper, the authors study position-based cryptography in the quantum setting. They show that if collaborating adversaries are allowed to pre-share an arbitrarily large entangled quantum state, then position-verification, and as a consequence position-based cryptography in general, is impossible (also) in the quantum setting. To this end, they prove that with the help of sufficient pre-shared entanglement, any non-local quantum computation, i.e., any computation that involves quantum inputs from two parties at different locations, can be performed instantaneously and without any communication, up to local corrections that need to be applied to the outputs.