The Research Of Secret Key Generation Based On Channel Impulse Response

Security is an especially important concern for wireless communication due to the public nature of wireless channel. Currently, security mechanisms of wireless network mainly rely upon traditional encryption schemes, which are assessed in terms of computational security. However, in mobile scenarios, secure distribution and management of the cryptographic keys can be a challenge. An alternative for achieving information-theoretically unconditional security at physical layer can be possible, which can be implemented by exploiting the inherent properties of wireless channel: reciprocity, spatial variations and temporal variations. In this thesis, we primarily study on the secret key generation from wireless channel itself. The main work of this paper can be summarized as follows:(1)Firstly, we compare three existing schemes of secret key generation, of which we focus on three metrics, including secret bit rate, bit disagreement ratio, randomness of generated key. Simulation results show that the level crossing secret key generation(LCA) scheme can extract random bits from channel measurements with low bit disagreement ratio at the tradeoff of reliably low secret bit rate. In the adaptive secret bit generation(ASBG) scheme, quantization is adapted to blocks. Then, Cascade is employed for reconciliation. It was shown that ABSG performs very close to the LCA scheme. The high-rate uncorrelated bit extraction(HRUBE) scheme employs multi-bit adaptive quantization and Karhunen-Loève Transform(KLT) to improve secret bit rate and the entropy of the generated bits, but sacrifices bit disagreement ratio.(2) A novel secret key generation method based on the LCA scheme is proposed. Compared to the LCA scheme, this proposed scheme accumulates the samples within each excursion for improved SNR in order to retain a low bit disagreement ratio. Furthermore, multi-bit quantization scheme is employed for the purpose of improving secret bit rate. Meanwhile, for information reconciliation, it adopts the mechanism in the LCA scheme where the positions of excursions are exchanged through public channel, which can be easily implemented. Extensive simulation results show that the proposed scheme can generate more secret bits with a low bit disagreement ratio in contrast with the LCA scheme. Besides, the generated secret keys of the proposed scheme can still pass the standard randomness test without privacy amplification.(3) We also propose to employ lattice whitening filter to do decorrelation instead of Karhunen-Loève Transform. It was reported that the implementation of Karhunen-Loève Transform is very sensitive to the correlation matrices, which require estimating in practice. When Karhunen-Loève Transform is independently implemented at two legitimate nodes, the bit disagreement ratio of the generated key at two nodes is unusually high. We show that the decorrelation process with lattice whitening filter can be independently implemented at two nodes without transmission of any information through the public channel, which can improve both the efficiency and security of the whole scheme.