Improving robustness of key extraction from wireless channels with differential techniques

Secure wireless communications typically rely on secret keys, which are difficult to establish in an ad hoc network without a key management infrastructure. Theoretically, the channel reciprocity and spatial decorrelation properties can be used to extract secret key, especially in a Rayleigh fading channel. However, as shown in some prior work by inserting or removing intermediate objects between the communication nodes, the strength of the secret key generated through such methods is low. Furthermore, the impact of small fluctuations also reduces the bit matching rate of such key agreement methods. In this paper, we propose a differential approach which uses the relative difference between two RSS values to determine the value of a secret bit. Additionally, the moving average method can be more easier and properly adapted to the differential approach which reduces the impact of small fluctuations. Experiment results and numerical evaluation show the proposed method has higher security strength, speed and matching rate comparing to a baseline from prior research work.