Relativistic quantum cryptography

Abstract: In this thesis we explore the benefits of relativistic constraints for cryptography. We first revisit non-communicating models and its applications in the context of interactive proofs and cryptography. We propose bit commitment protocols whose security hinges on communication constraints and investigate its limitations. We explain how some non-communicating models can be justified by special relativity and study the limitations of such models. In particular, we present a framework for analysing security of multiround relativistic protocols. The second part of the thesis is dedicated to analysing specific protocols. We start by considering a recently proposed two-round quantum bit commitment protocol. We propose a fault-tolerant variant of the protocol, present a complete security analysis and report on an experimental implementation performed in collaboration with an experimental group at the University of Geneva. We also propose a new, multiround classical bit commitment protocol and prove its security against classical adversaries. This demonstrates that in the classical world an arbitrarily long commitment can be achieved even if the agents are restricted to occupy a finite region of space. Moreover, the protocol is easy to implement and we report on an experiment performed in collaboration with the Geneva group.