Device-independent quantum key distribution

TL;DR

This thesis explores two approaches to device-independent quantum key distribution, establishing security under specific non-signalling and quantum constraints, and demonstrating the existence of joint attacks without these restrictions.

Contribution

It provides a generic security proof for device-independent QKD under non-signalling and quantum constraints, extending the security analysis of existing protocols.

Findings

Security can be achieved with additional non-signalling or quantum constraints.

Without restrictions, non-signalling adversaries can always mount successful joint attacks.

The security proof applies to an existing QKD protocol, confirming its robustness.

Abstract

In this thesis, we study two approaches to achieve device-independent quantum key distribution: in the first approach, the adversary can distribute any system to the honest parties that cannot be used to communicate between the three of them, i.e., it must be non-signalling. In the second approach, we limit the adversary to strategies which can be implemented using quantum physics. For both approaches, we show how device-independent quantum key distribution can be achieved when imposing an additional condition. In the non-signalling case this additional requirement is that communication is impossible between all pairwise subsystems of the honest parties, while, in the quantum case, we demand that measurements on different subsystems must commute. We give a generic security proof for device-independent quantum key distribution in these cases and apply it to an existing quantum key distribution protocol, thus proving its security even in this setting. We also show that, without any additional such restriction there always exists a successful joint attack by a non-signalling adversary.