This work introduces security for unsourced random access (URA) via a physical-layer security approach. To achieve confidentiality, the proposed system opportunistically exploits intrinsic features of feedback-aided URA without altering its original structure or operational characteristics. As a result, the system preserves URA's efficiency, including low delay and minimal signaling overhead, while ensuring secure communication. To secure transmission, each user generates a secret key from a feedback signal broadcast by the BS in a previous transmission round, which depends on the BS-user channel and can thus be treated as private. Each user then encrypts its data using the secret key before transmission. Along with the encrypted data, only the parity bits of the LDPC-encoded key are transmitted, enabling secret key recovery at the legitimate receiver via Slepian-Wolf decoding with side information. We propose a receiver algorithm to recover both the encrypted data and the encoded secret key at the legitimate receiver. We further present a theoretical analysis to derive analytical error probabilities for both the legitimate receiver and the passive eavesdropper, as well as to quantify the additional load imposed by the security measures on the URA system. It is shown, based on both theoretical analysis and simulation results, that meaningful secrecy is achieved with only negligible extra overhead compared to the standard URA system.

翻译：本文通过物理层安全方法为无源随机接入（URA）引入安全性。为保障机密性，所提系统在保持URA原始结构和运行特性不变的前提下，机会性地利用反馈辅助URA的固有特性。因此，该方案在确保安全通信的同时，保留了URA的低延迟与最小信令开销等优势。在传输过程中，每个用户根据基站（BS）在前一轮传输广播的反馈信号生成密钥，该密钥依赖于BS-用户信道特性，因此可视为私有信息。用户随后使用该密钥对数据进行加密传输。除加密数据外，仅传输经LDPC编码后密钥的校验位，使得合法接收端可通过带边信息的Slepian-Wolf解码恢复密钥。我们提出一种接收机算法，用于在合法接收端同时恢复加密数据与编码密钥。进一步通过理论分析推导合法接收端与被动窃听端的分析误码概率，并量化安全措施对URA系统带来的额外负荷。基于理论分析与仿真结果表明，相较于标准URA系统，本方案仅需极小的额外开销即可实现有意义的保密性。