  A common approach for introducing security at the physical layer is to rely
on the channel variations of the wireless environment. This type of approach is
not always suitable for wireless networks where the channel remains static for
most of the network lifetime. For these scenarios, a channel independent
physical layer security measure is more appropriate which will rely on a secret
known to the sender and the receiver but not to the eavesdropper. In this
paper, we propose CD-PHY, a physical layer security technique that exploits the
constellation diversity of wireless networks which is independent of the
channel variations. The sender and the receiver use a custom bit sequence to
constellation symbol mapping to secure the physical layer communication which
is not known a priori to the eavesdropper. Through theoretical modeling and
experimental simulation, we show that this information theoretic construct can
achieve Shannon secrecy and any brute force attack from the eavesdropper incurs
high overhead and minuscule probability of success. Our results also show that
the high bit error rate also makes decoding practically infeasible for the
eavesdropper, thus securing the communication between the sender and receiver.
