Capacity results, coordination resources, and super-activation in wiretap channels

Availability of channel state information, especially to non-legitimate users, is one major challenge for secure communication in wireless systems. For arbitrarily varying channels (AVC), coordination resources such as common randomness have been shown to be important for reliable communication; especially for symmetrizable AVCs. In this paper, the arbitrarily varying wiretap channel (AVWC) with active wiretapper is studied. Such an wiretapper may or may not exploit his knowledge about the coordination resources to control the channel conditions. Secrecy capacity results are derived for different forms of coordination resources including common randomness and correlated sources. Finally, it is demonstrated how two orthogonal AVWCs, each with zero secrecy capacity, i.e., useless for secure transmission, can be super-activated to a useful channel allowing for secure communication at non-zero secrecy rates.