7 research outputs found
Device-Independent Relativistic Quantum Bit Commitment
We examine the possibility of device-independent relativistic quantum bit
commitment. We note the potential threat of {\it location attacks}, in which
the behaviour of untrusted devices used in relativistic quantum cryptography
depends on their space-time location. We describe relativistic quantum bit
commitment schemes that are immune to these attacks, and show that these
schemes offer device-independent security against hypothetical post-quantum
adversaries subject only to the no-signalling principle. We compare a
relativistic classical bit commitment scheme with similar features, and note
some possible advantages of the quantum schemes
Unconditionally Secure Bit Commitment by Transmitting Measurement Outcomes
We propose a new unconditionally secure bit commitment scheme based on
Minkowski causality and the properties of quantum information. The receiving
party sends a number of randomly chosen BB84 qubits to the committer at a given
point in space-time. The committer carries out measurements in one of the two
BB84 bases, depending on the committed bit value, and transmits the outcomes
securely at light speed in opposite directions to remote agents. These agents
unveil the bit by returning the outcomes to adjacent agents of the receiver.
The security proofs rely only on simple properties of quantum information and
the impossibility of superluminal signalling.Comment: Discussion expanded pedagogically in response to referee comment
Location-Oblivious Data Transfer with Flying Entangled Qudits
We present a simple and practical quantum protocol involving two mistrustful
agencies in Minkowski space, which allows Alice to transfer data to Bob at a
spacetime location that neither can predict in advance. The location depends on
both Alice's and Bob's actions. The protocol guarantees unconditionally to
Alice that Bob learns the data at a randomly determined location; it guarantees
to Bob that Alice will not learn the transfer location even after the protocol
is complete.
The task implemented, transferring data at a space-time location that remains
hidden from the transferrer, has no precise analogue in non-relativistic
quantum cryptography. It illustrates further the scope for novel cryptographic
applications of relativistic quantum theory.Comment: References updated. Published versio
An optical implementation of quantum bit commitment using infinite-dimensional systems
Unconditionally secure quantum bit commitment (QBC) was widely believed to be
impossible for more than two decades. But recently, basing on an anomalous
behavior found in quantum steering, we proposed a QBC protocol which can be
unconditionally secure in principle. The protocol requires the use of
infinite-dimensional systems, thus it may seem less feasible at first glance.
Here we show that such infinite-dimensional systems can be implemented with
quantum optical methods, and propose an experimental scheme using Mach-Zehnder
interferometer.Comment: 6 pages, 1 figur
Relativistic quantum cryptography
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.Comment: 123 pages, 9 figures, many protocols, a couple of theorems, certainly
not enough commas. PhD thesis supervised by Stephanie Wehner at Centre for
Quantum Technologies, Singapor