Efficient key generation leveraging channel reciprocity and balanced gray code

Key generation leveraging wireless channel reciprocity can establish secret keys from unauthenticated broadcast channels and thus protect the communication of wireless networks. However, in real environments, the measurements collected by the involved transceivers might have many discrepancies due to the non-simultaneous directional measurements and other factors, such as hardware differences and asymmetric interferences. Meanwhile, if the multi-level quantization in conjunction with source coding is implemented to convert measurements to bits, the resulting high bit mismatch rate makes key agreement inefficient and insecure. In this paper, key generation schemes leveraging channel reciprocity and balanced gray code are proposed. To enhance the efficiency of key generation, an efficient encoding scheme based on balanced gray code is carried out during key generation. The proposed encoding scheme can simultaneously reduce the bit mismatch rate and improve the secret bit rate. In addition, the code book is reusable once it is generated. The proposed key generation schemes can be classified into the uniform and non-uniform schemes according to different quantization processes. Several experiments in real mobile environments are conducted to validate the proposed schemes. The received signal strength measurements are extracted from heterogeneous devices as statistics of channel states in each experiment. The results of these experiments show that (1) the proposed encoding scheme significantly enhances the efficiency of key generation; (2) both the uniform and non-uniform schemes can efficiently generate secret keys between heterogeneous transceivers.