  Physical layer key generation from the wireless channel is an emerging area
of interest to provide confidentiality and authentication. One of the main
challenges in this domain is to increase the length of the secret key while
maintaining its randomness and uniformity. In this work, new dimensions for
wireless channel-based key generation are proposed for orthogonal frequency
division multiplexing (OFDM) systems. The novel perspective of the proposed
work lies in the generation of key bits not only from the magnitudes of OFDM
subchannels as it has conventionally been done but also from the number and
positions of those subchannels whose channel gains are above the mean of the
respective subblock. The effectiveness of the proposed algorithms is evaluated
in terms of key generation rate and key mismatch rate. Additionally, a
statistical test suite offered by the National Institute of Standards and
Technology is used to evaluate the randomness of the generated key bits. It is
shown in the simulation results that the involvement of the proposed dimensions
can double the key generation rate compared to conventional algorithms.
