[Paper Review] Multiparty Quantum Key Agreement based on Quantum Secret Direct Communication with GHZ states

Guo-Jyun Zeng, Kuan-Hung Chen+3 more|arXiv (Cornell University)|Feb 2, 2016

Quantum Information and Cryptography20 references3 citations

TL;DR

This paper proposes a novel multiparty quantum key agreement (MQKA) protocol using Greenberger-Horne-Zeilinger (GHZ) states and multicast communication to enhance efficiency and security. By enabling all participants to simultaneously transmit their key contributions via multicast, the protocol reduces transmission rounds, qubit consumption, and delay compared to unicast-based existing methods, achieving linear resource scaling and robust resistance to internal and external eavesdropping attacks.

ABSTRACT

Quantum Key Agreement (QKA) signifies that two or more participants together generate a key and QKA has to satisfy the following conditions: 1 Every participant can change the key and the key is not decided by any participant individually. 2 Only participants can know the key; nonparticipants cannot get the key through illegal means. Because of the condition 1 of participating together, it makes transport inefficient in the current mainstream protocols. They use unicast to exchange messages one by one, so it will considerably limit transmission efficiency and increase cost time spent. This study proposes a protocol based on Multiparty Quantum Secret Direct Communication (MQSDC) with multicast. In addition to satisfying the above conditions, it uses multicast to not only achieve the effect and purpose of QKA, but also to defend against internal and external attacks at the same time. In regard to resource consumption, this study involves linear growth and is more efficient than other mainstream protocols which employ exponential growth.

Motivation & Objective

• Address the inefficiency of existing unicast-based multiparty quantum key agreement (MQKA) protocols that suffer from high transmission rounds and resource consumption.
• Overcome the limitation of sequential message exchange in current MQKA protocols by introducing a multicast communication model to enable simultaneous key contribution from all participants.
• Ensure that every participant actively contributes to key generation, satisfying the core condition of QKA that no single participant can predetermine the final key.
• Achieve unconditional security against both external eavesdropping and internal attacks through channel checking and entanglement-based verification.
• Demonstrate superior performance in transmission efficiency, qubit usage, and delay compared to state-of-the-art unicast-based MQKA protocols.

Proposed method

• Utilizes three-qubit Greenberger-Horne-Zeilinger (GHZ) states as the entangled resource for encoding and transmitting classical key information.
• Employs a multicast communication model where the key generator broadcasts their operations to all participants simultaneously, reducing the number of transmission rounds.
• Each participant performs a unitary operation on their qubit based on their desired key bit and then transmits the entire sequence back to the key generator via multicast.
• The protocol uses a channel-checking mechanism where 10 randomly selected qubits per transmission are used to detect eavesdropping by comparing measurement results in the Z and X bases.
• The final key is generated using a formula that combines all participants' operations, ensuring collective contribution and preventing individual key predetermination.
• Security is verified through analysis of both external eavesdropping (via measurement basis comparison) and internal attacks (e.g., dishonest participants altering operations), with detection via measurement basis mismatch.

Experimental results

Research questions

• RQ1 Can a multicast-based MQKA protocol reduce transmission rounds and resource consumption compared to existing unicast-based MQKA protocols?
• RQ2 Does the proposed protocol maintain security against both external eavesdropping and internal attacks while ensuring all participants contribute to the final key?
• RQ3 How does the proposed protocol compare quantitatively in terms of qubit usage, transmission delay, and number of transmissions with existing MQKA protocols?
• RQ4 Can the protocol achieve linear resource scaling instead of exponential growth, improving efficiency for large-scale multiparty key agreement?
• RQ5 Is it possible to simultaneously transmit key contributions from all participants using GHZ states and multicast, without compromising security or correctness?

Key findings

• The proposed protocol reduces the number of transmissions to (N−1)×2 for N participants, significantly fewer than unicast protocols like Shi and Zhong [9] and Sun et al. [16], which require N transmissions.
• The protocol consumes only (N−1)×2×2×10 = 40(N−1) qubits for channel checking, which is substantially less than protocols like Sun et al. [17], which require ⌈(N−1)/2⌉×2×N×4×10 qubits.
• Transmission delay is minimized to 4 time units for 2-bit key agreement, outperforming protocols like Shi and Zhong [9] (N time units) and Shukla et al. [15] (2N time units).
• The protocol achieves linear resource growth in terms of qubits and transmissions, unlike exponential growth in some existing protocols, making it scalable for large N.
• Security analysis confirms that both external eavesdroppers and internal adversaries (e.g., dishonest participants) can be detected through basis mismatch in channel-checking qubits.
• The protocol successfully satisfies both core QKA conditions: collective key generation and resistance to unauthorized access, with all participants actively contributing via unitary operations.