Contextuality offers security

TL;DR

This paper introduces a novel quantum cryptographic protocol based on contextuality, demonstrating that the fundamental quantum feature of information-disturbance trade-off can be used to ensure security, even with untrusted devices.

Contribution

It presents the first operational protocol leveraging quantum contextuality, specifically Kochen-Specker paradox conditions, for device-independent cryptography.

Findings

Secure key can be extracted using systems exhibiting Kochen-Specker paradox conditions.

The protocol is the first to directly implement the fundamental quantum trade-off between information gain and disturbance.

It provides a practical, device-independent quantum cryptographic scheme compatible with current technology.

Abstract

The discovery of quantum key distribution by Bennett and Brassard (BB84) bases on the fundamental quantum feature: incompatibility of measurements of quantum non-commuting observables. In 1991 Ekert showed that cryptographic key can be generated at a distance with help of entangled (correlated) quantum particles. Recently Barrett, Hardy and Kent showed that the non-locality used by Ekert is itself a good resource of cryptographic key even beyond quantum mechanics. Their result paved the way to new generation of quantum cryptographic protocols - secure even if the devices are built by the very eavesdropper. However, there is a question, which is fundamental from both practical and philosophical point of view: does Nature offer security on operational level based on the original concept behind quantum cryptography - that information gain about one bservables must cause disturbance to another, incompatible one? Here we resolve this problem by using in place of non-locality another striking feature of quantum world - contextuality. It is a strong version of incompatibility manifested in the famous Kochen-Specker paradox. The crucial concept is the use of a new class of families of bipartite probability distributions which locally exhibit the Kochen-Specker paradox conditions and, in addition, exhibit perfect correlations. We show that if two persons share systems described by such a family then they can extract secure key. This is the first operational protocol that directly implements the fundamental feature of Nature: the information gain vs. disturbance trade-off. At the same time it provides natural device-independent cryptographic scheme within quantum mechanics suitable for current technology.