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EPJ Quantum Technology

Proof-of-principle demonstration of semi-quantum key distribution based on the Mirror protocol

Siyu Han, Yutao Huang, Shang Mi, Xiaojuan Qin, Jindong Wang, Ya‐Fei Yu, Zhengjun Wei, Zhi‐Ming Zhang

Published Dec 1, 2021• 18 citations
Publisher

Abstract

Abstract Semi-quantum key distribution (SQKD) is used to establish a string of shared secret keys between a quantum party and a classical party. Here, we report the first proof-of-principle experimental demonstration of SQKD based on the Mirror protocol, which is the most experimentally feasible SQKD protocol, and equipped with time-phase encoding scheme employing the method of selective modulation. The experiment was performed at a repetition frequency of 62.5 MHz and a high raw key rate arrived at 69.8 kbps, and the average quantum bit error rate was found to be 4.56% and 2.78% for the “SWAP-x-Z” ( $\mathrm{x}\in \{01,10\}$ x ∈ { 01 , 10 } ) and the “CTRL-X”, respectively. The results demonstrate the feasibility of our system, and this study is helpful for future research on SQKD experiments.

DOI
10.1140/epjqt/s40507-021-00117-8

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Abstract Semi-quantum key distribution (SQKD) is used to establish a string of shared secret keys between a quantum party and a classical party. Here, we report the first proof-of-principle experimental demonstration of SQKD based on the Mirror protocol, which is the most experimentally feasible SQKD protocol, and equipped with time-phase encoding scheme employing the method of selective modulation. The experiment was performed at a repetition frequency of 62.5 MHz and a high raw key rate arrived at 69.8 kbps, and the average quantum bit error rate was found to be 4.56% and 2.78% for the “SWAP-x-Z” ( x∈{01,10}\mathrm{x}\in \{01,10\}x∈{01,10} x ∈ { 01 , 10 } ) and the “CTRL-X”, respectively. The results demonstrate the feasibility of our system, and this study is helpful for future research on SQKD experiments.
Semi-quantum key distribution (SQKD) allows a quantum user and a classical user to share a string of secret keys, providing support for application scenarios that cannot withstand the high cost of quantum resources. In this paper, we propose what we believe to be the first proof-of-principle experimental demonstration of free space SQKD based on the single-state protocol, which is equipped with polarization encoding scheme employing the method of selective modulation. During the half-hour test time for each operation, the overall experiment obtained the original key rate of 107.2 kbps at the repetition frequency of 100 MHz, and the average bit error rate was determined to be 1.65% for CTRL operation and 0.64% for SIFT operation. The experimental results indicate that our system exhibits commendable performance and stability at a low bit error rate that represents a significant initial stride toward the future practical deployment of SQKD systems within free-space channels.
Decoy state semi-quantum key distribution (SQKD) has been proposed as a method aimed at significantly enhancing the security and performance of practical semi-quantum key distribution systems. However, the gap between theory and experiment remains open. Herein, we propose the decoy state setting and experimental scheme for the mirror protocol and conduct the proof-of-principle demonstration experiment of the decoy state mirror protocol. The simulation results, obtained under experimental conditions, demonstrate that no key generation rate can be generated under the conditions of the Gottesman-Lo-Lütkenhaus-Preskill (GLLP) and one-decoy state, while valid key generation rates are achievable within a fiber transmission distance of 19.1 km under the weak and vacuum states. Furthermore, it was experimentally verified that a key generation rate of 406 bits/s can be achieved under the combined conditions of weak and vacuum states and a 10 km fiber channel. As the first, to the best of our knowledge, proof-of-principle demonstration of the decoy state mirror protocol, this study lays a foundation for the practical security analysis of SQKD from an experimental perspective and serves as an important starting point for the practical verification in this field.
Semiquantum key distribution (SQKD) allows two parties (Alice and Bob) to create a shared secret key, even if one of these parties (say, Alice) is classical. However, most SQKD protocols suffer from severe practical security problems when implemented using photons. The recently developed “Mirror protocol” [1] is an experimentally feasible SQKD protocol overcoming those drawbacks. The Mirror protocol was proven robust (namely, it was proven secure against a limited class of attacks including all noiseless attacks), but its security in case some noise is allowed (natural or due to eavesdropping) has not been proved yet. Here we prove security of the Mirror protocol against a wide class of quantum attacks (the “collective attacks”), and we evaluate the allowed noise threshold and the resulting key rate.
Semi-quantum key distribution (SQKD) allows sharing random keys between a quantum user and a classical user, which significantly saves user resources, especially when using the Single-state protocol. However, the operation of the classical user, which involves measurement and resending using the Single-state protocol, presents technical difficulties in experiment and there is a security vulnerability of "tagged" attack in theory. To solve these problems, in our work, based on the Single-state protocol, we propose the "selective modulation" method and successfully implement a phase-encoded semi-quantum key distribution system. The system operates at a frequency of 100MHz and an average photon number of 0.1. The interference contrast achieved 97.45%, the average quantum bit error rate was 1.20%, and the raw key rate reached 88Kbps. Our experimental results demonstrate the feasibility and stability of the proposed phase-encoded SQKD system. Furthermore, we conducted an analysis of the "selective modulation" scheme in terms of quantum state evolution to assess the security of our system and ultimately proved that it can resist "tagged" attack. The classical user of our system requires only two optical devices and operates without relying on full quantum capabilities, thereby enhancing its application potential in quantum networks. This work validates the feasibility of SQKD experiments and provides ideas for future research on SQKD experiments and security studies.
Quantum key distribution (QKD) protocols make it possible for two quantum parties to generate a secret shared key. Semiquantum key distribution (SQKD) protocols, such as ``QKD with classical Bob'' and ``QKD with classical Alice'' (that have both been proven robust), achieve this goal even if one of the parties is classical. However, existing SQKD protocols are not experimentally feasible with current technology. Here we suggest a protocol, ``Classical Alice with a controllable mirror,'' that can be experimentally implemented with current technology (using four-level systems instead of qubits), and we prove it to be robust.
A semiquantum key distribution (SQKD) protocol makes it possible for a quantum party and a classical party to generate a secret shared key. However, many existing SQKD protocols are not experimentally feasible in a secure way using current technology. An experimentally feasible SQKD protocol, "classical Alice with a controllable mirror" (the "Mirror protocol"), has recently been presented and proved completely robust, but it is more complicated than other SQKD protocols. Here we prove a simpler variant of the Mirror protocol (the "simplified Mirror protocol") to be completely non-robust by presenting two possible attacks against it. Our results show that the complexity of the Mirror protocol is at least partly necessary for achieving robustness.