Li-Hua Gong

Quantum identity authentication (QIA) has emerged as a crucial technology for secure communication systems, particularly in the burgeoning era of quantum communications. This paper proposes a novel QIA protocol based on non-classical characteristics of squeezed light fields. By exploiting the quantum noise reduction properties of quadrature squeezed coherent states, the protocol fundamentally thwarts eavesdropping attempts by Heisenberg-limited uncertainty constraints. The fidelity parameter for decoy states is utilized to detect spoofing attacks, and the dynamic key update mechanism fundamentally eliminates vulnerabilities caused by key reuse. Security information ratio analysis shows that the protocol is able to resist Gaussian-cloner attacks and detect eavesdropping. Moreover, the security threshold can be further enhanced with higher squeezing, allowing tunable protection levels adaptable to different threat scenarios. Compared with binary-squeezed protocols, our proposed four-direction (quaternary-dimensional) squeezing halves the eavesdropper's guessing probability and enlarges the fidelity gap by 29%, tightening the discrimination threshold without relying on extra hardware, thus facilitating practical implementation.

A new multi‐party semi‐quantum private comparison protocol of size relation is designed based on d ‐level GHZ states. Multiple classical participants could compare their privacies while keeping them secure under an ideal environment. Compared with some similar protocols, the classical participants in the designed protocol do not need to prepare and measure quantum states. Besides, the qubit efficiency of the protocol reaches 33.33%. It is demonstrated that the output result of the proposed protocol is correct. Finally, security analysis manifests that the proposed protocol behaves well in withstanding intercept‐resend attack, measure‐resend attack, entanglement attack, Trojan horse attack, and so on.

Based on the decoherence‐free states, two multi‐party semi‐quantum private comparison protocols are proposed to counteract collective noises. One can resist the collective‐dephasing noise well, and the other can resist the collective‐rotation noise. With the assistance of a semi‐honest third party (TP), multiple classical participants with restricted quantum abilities can compare their secret information by performing the proposed protocols once. It is manifested that the proposed protocols can resist both external attacks and internal attacks. Additionally, the operations in the multi‐party semi‐quantum private comparison protocols are simulated on the IBM Quantum Experience.