Intrinsically secure physical layer cryptography in wireless networks

Due to the enormous spreading of applied wireless networks, security is actually one of the most important issues for telecommunications. One of the main issue in the field of securing wireless information exchanging is the initial common knowledge between source and destination. A shared secret is normally mandatory in order to decide the encryption (algorithm or code or key) of the information stream. It is usual to exchange this common a priori knowledge by using a “secure” channel. Nowadays a secure wireless channel is not possible. In fact normally the common a priori knowledge is already established (but this is not secure) or by using a nonradio channel (that implies a waste of time and resource). The information is encrypted by means of a private key that must be known by both the transmitter and the receiver. One of the main weak point about security is the private key exchanging interval. The key cannot be public and cannot be known a priori. The problem is how to exchange this private key through a totally secure wireless channel. This contribution deals with the review of the main physical layer techniques for encrypting the information and the proposal of a new physical layer technique ensuring secure communication in a full wireless environment without any a priori common knowledge between the legal users.