Intelligent Reflecting Surface-Assisted Wireless Key Generation for Low-Entropy Environments

Physical layer key generation is a promising candidate for cryptographic key establishment between two wireless communication parties. It offers information-theoretic security and is an attractive alternative to public-key techniques. Here, the inherent randomness of wireless radio channels is used as a shared entropy source to generate cryptographic key material. However, practical implementations often suffer from static channel conditions which exhibit a limited amount of randomness. In the past, considerable research efforts have been made to address this fundamental limitation. However, current solutions are not generic or require dedicated hardware extensions such as reconfigurable antennas. In this paper, we propose a novel wireless key generation architecture based on randomized channel responses from Intelligent Reflecting Surfaces (IRS). Due to its passive nature, a cooperative IRS is well-suited to provide randomness for conventional low-resource radios. We conduct the first practical studies to successfully demonstrate IRS-based physical-layer key generation with a 2x2 MIMO-OFDM system. In a static environment, using a single subcarrier only, our IRS-assisted prototype system achieves a KGR of 20.75 bps with 9.3% KDR after quantization, while passing standard randomness tests.