Secret Key Extraction Using Stable Channel Impulse Response in OFDM Wireless Networks

ABSTRACT This work proposes a secret key extraction technique from the complex impulse response (CIR) for secure orthogonal frequency division multiplexing (OFDM) wireless communication systems. Using time division duplexing (TDD), the legitimate transceivers exchange pilot tones within the channel coherence time to estimate their CIRs, from which the dominant peaks are selected and quantised into binary sequences using a mean‐referenced Heaviside rule. Simulations are conducted in MATLAB for OFDM systems over Additive White Gaussian Noise (AWGN) and Rayleigh fading channels with Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK) modulation schemes. The proposed method is evaluated in terms of randomness, key disagreement rate (KDR), and key generation rate (KGR). For key lengths of 128 bits, 100,000 bits, and 1,000,000 bits, the generated key sequences pass 8, 9 and 15 tests, respectively, in the National Institute of Standards and Technology (NIST) statistical test suite, with all p ‐values greater than 0.01. Since the simulations are performed under ideal reciprocal channel conditions, the keys generated by the two legitimate users are identical, resulting in a KDR of 0 prior to any reconciliation process. In addition, because 16 dominant CIR peaks are extracted from each realisation and each peak contributes one bit, the proposed method achieves a constant KGR of 16 bits per CIR realisation. The results show that the proposed scheme provides a scalable and deterministic key generation mechanism with strong randomness, zero disagreement in simulation, and controllable generation efficiency.