Secure and Controllable Secret Key Generation Through CSI Obfuscation Matrix Encapsulation

Physical-layer key generation has emerged as a promising avenue for establishing secret keys using reciprocal channel measurements between wireless devices. However, channel reciprocity may suffer degradation from ambient noise and cause mismatched secret bits, while existing methods mitigating this issue may yet face limitations in key efficiency. The root cause behind such limitations is the heavy reliance on channel measurements, which can be naturally susceptible to channel non-reciprocity attributed to environmental factors. Instead of direct key extraction from channel measurements, we seek to share a pre-defined key and utilize channel measurements as a bearer to facilitate key transmission. We propose an accurate and efficient key generation method (KeyCome) to ensure secure key sharing by encapsulating it with channel state information (CSI) obfuscation matrices through circulant convolution. To this end, we develop a reliable key derivation through a quadratic programming method with matrix equilibration, ensuring stable and rapid solutions. Notably, the transmitter can control the key beforehand for enhanced communication efficiency and combine it with an error correction mechanism for accurate key derivation. Furthermore, a lightweight reconciliation scheme is designed to minimize mismatched bits caused by occasional non-reciprocity. Comprehensive experiments demonstrate KeyCome's high accuracy and efficiency in key generation.