  Current security techniques can be implemented either by requiring a secret
key exchange or depending on assumptions about the communication channels. In
this paper, we show that, by using a physical layer technique known as
artificial noise, it is feasible to protect secret data without any form of
secret key exchange and any restriction on the communication channels.
Specifically, we analyze how the artificial noise can achieve practical
secrecy. By treating the artificial noise as an unshared one-time pad secret
key, we show that the proposed scheme also achieves Shannon's perfect secrecy.
Moreover, we show that achieving perfect secrecy is much easier than ensuring
non-zero secrecy capacity, especially when the eavesdropper has more antennas
than the transmitter. Focusing on the practical applications, we show that
practical secrecy and strong secrecy can be guaranteed even if the eavesdropper
attempts to remove the artificial noise. We finally show the connections
between traditional cryptography and physical layer security.
