Long distance two-party quantum cryptography made simple

TL;DR

This paper presents a simplified approach to long-distance two-party quantum cryptography using classical cryptography techniques in a network of quantum nodes, enabling secure communication without complex quantum procedures.

Contribution

It introduces a novel method for secure two-party cryptography over long distances using only neighboring quantum links and classical cryptography principles, avoiding entanglement swapping.

Findings

Oblivious transfer achievable if an honest path exists between nodes.

Security can be maintained with relaxed assumptions, combining classical cryptography and computational hardness.

The protocol does not require technologically difficult quantum procedures like entanglement swapping.

Abstract

Any two-party cryptographic primitive can be implemented using quantum communication under the assumption that it is difficult to store a large number of quantum states perfectly. However, achieving reliable quantum communication over long distances remains a difficult problem. Here, we consider a large network of nodes with only neighboring quantum links. We exploit properties of this cloud of nodes to enable any two nodes to achieve security even if they are not directly connected. Our results are based on techniques from classical cryptography and do not resort to technologically difficult procedures like entanglement swapping. More precisely, we show that oblivious transfer can be achieved in such a network if and only if there exists a path in the network between the sender and the receiver along which all nodes are honest. Finally, we show that useful notions of security can still be achieved when we relax the assumption of an honest path. For example, we show that we can combine our protocol for oblivious transfer with computational assumptions such that we obtain security if either there exists an honest path, or, as a backup, at least the adversary cannot solve a computational problem.