This work introduces security for unsourced random access (URA) by employing physical layer security techniques. To achieve confidentiality, the proposed system opportunistically exploits intrinsic features of feedback-aided URA without adding any overhead or altering its original structure or operational characteristics. As a result, the proposed system preserves the low-cost advantages of URA, including low delay and minimal signaling overhead, while providing secure communication. To secure transmission, each user generates a secret key from a feedback signal broadcast by the BS in a previous transmission round. This feedback depends on the BS-user channel, making it a private signal for each user. Secure transmission is achieved not only through encryption using the secret key, but also by transmitting only the parity bits of the LDPC-encoded key, thereby enabling its recovery at the legitimate receiver via Slepian-Wolf decoding with side information. For reception, a receiver algorithm is designed for the legitimate receiver, and a leakage analysis is provided to quantify the information available to the eavesdropper. The simulation results show that meaningful secrecy is achieved in URA without modifying its structure.

翻译：本文通过采用物理层安全技术，为无源随机接入（URA）引入了安全性。为实现保密性，所提系统机会性地利用了反馈辅助URA的内在特征，无需增加任何开销或改变其原始结构及运行特性。因此，该系统在提供安全通信的同时，保留了URA的低成本优势，包括低延迟和最小信令开销。为保障传输安全，每个用户根据基站在前一轮传输中广播的反馈信号生成密钥。该反馈依赖于基站与用户之间的信道，从而成为每个用户的私有信号。安全传输不仅通过密钥加密实现，还通过仅传输LDPC编码密钥的校验位来达成，这使得合法接收方能够借助边信息通过Slepian-Wolf解码恢复密钥。在接收端，为合法接收方设计了接收算法，并提供了泄露分析以量化窃听者可获取的信息。仿真结果表明，在不修改URA结构的前提下，实现了有意义的保密性。