Physical layer security can provide alternative means for securing the exchange of confidential messages in wireless applications without the need for private (secret) keys. The seminal works of Wyner on the wiretap channel, Csizar and Korner on the broadcasting channel with confidential messages and Leung-Yan-Cheong and Helman on the Gaussian wiretap channel, have established that opportunities for perfectly secure communications can be substantiated when the eavesdropping channel is degraded with respect to the main source-destination channel. Recently, there have been considerable efforts devoted to generalising this result to the wireless fading channel, the relay channel and to multi-user scenarios. Yet, despite the significant research efforts and results in the last 10 years, physical layer security is still considered a primarily theoretical area of research.

In this talk, we will alternatively place the focus on the design of practical systems; I will present a number of systems in which secrecy rates suitable for real applications can be achieved. First, we will consider broadcasting multi-user networks with passive (interception of the broadcast channel) and active (interception of the broadcast channel and false feedback) eavesdroppers. It will be demonstrated that as long as the legitimate users outnumber the adversaries, substantial secrecy rates can be attained. Furthermore, it will be shown that such networks become insensitive to the activeness or passiveness of the attack in the high signal to noise ratio regime. Secondly, I will outline a proof-of-concept system proposal for achieving perfect secrecy exploiting topological and mobility asymmetries between a legitimate user and potential adversaries, in the non-degraded eavesdropping channel case. Finally, we will re-visit interference assisted approaches and investigate the design of optimal jamming signals for common M-QAM and M-PSK systems.