Dense-Coding Attack on Three-Party Quantum Key Distribution Protocols

TL;DR

This paper reveals a simple dense-coding attack that compromises the security of two recent three-party quantum key distribution protocols, allowing an eavesdropper to fully obtain session keys without detection.

Contribution

It introduces a novel dense-coding attack on specific quantum key distribution protocols and analyzes its effectiveness and implications for protocol security.

Findings

The attack allows complete key recovery without detection.

The protocols are vulnerable due to their susceptibility to dense-coding strategies.

Possible improvements to enhance security are discussed.

Abstract

Cryptanalysis is an important branch in the study of cryptography, including both the classical cryptography and the quantum one. In this paper we analyze the security of two three-party quantum key distribution protocols (QKDPs) proposed recently, and point out that they are susceptible to a simple and effective attack, i.e. the dense-coding attack. It is shown that the eavesdropper Eve can totally obtain the session key by sending entangled qubits as the fake signal to Alice and performing collective measurements after Alice's encoding. The attack process is just like a dense-coding communication between Eve and Alice, where a special measurement basis is employed. Furthermore, this attack does not introduce any errors to the transmitted information and consequently will not be discovered by Alice and Bob. The attack strategy is described in detail and a proof for its correctness is given. At last, the root of this insecurity and a possible way to improve these protocols are discussed.