  This paper investigates the problem of secret key generation over a wiretap
channel when the terminals observe correlated sources. These sources are
independent of the main channel and the users overhear them before the
transmission takes place. A novel achievable scheme is proposed, and its
optimality is shown under certain less-noisy conditions. This result improves
upon the existing literature where the more stringent condition of degradedness
is required. Furthermore, numerical evaluation of the proposed scheme and
previously reported results for a binary model are presented; a comparison of
the numerical bounds provides insights on the benefit of the novel scheme.
