  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.
