  We proposed a new physical layer technique that can enhance the security of
cooperative relay communications. The proposed approach modifies the decoded
message at the relay according to the unique channel state between the relay
and the destination such that the destination can utilize the modified message
to its advantage while the eavesdropper cannot. We present a practical method
for securely sharing the modification rule between the legitimate partners and
present the secrecy outage probability in a quasi-static fading channel. It is
demonstrated that the proposed scheme can provide a significant improvement
over other schemes when the relay can successfully decode the source message.
