  We explore the additional security obtained by noise at the physical layer in
a wiretap channel model setting. Security enhancements at the physical layer
have been proposed recently using a secrecy metric based on the degrees of
freedom that an attacker has with respect to the sent ciphertext. Prior work
focused on cases in which the wiretap channel could be modeled as statistically
independent packet erasure channels for the legitimate receiver and an
eavesdropper. In this paper, we go beyond the state-of-the-art by addressing
correlated erasure events across the two communication channels. The resulting
security enhancement is presented as a function of the correlation coefficient
and the erasure probabilities for both channels. It is shown that security
improvements are achievable by means of judicious physical-layer design even
when the eavesdropper has a better channel than the legitimate receiver. The
only case in which this assertion may not hold is when erasures are highly
correlated across channels. However, we are able to prove that correlation
cannot nullify the expected security enhancement if the channel quality of the
legitimate receiver is strictly better than that of the eavesdropper.
