Physical Layer Security – Wiretap Channels with Active Adversary

Secure communication in a potentially hostile environment is becoming more and more critical. The Arbitrarily Varying Wiretap Channel (AVWC) provides information-theoretical bounds on how much information can be exchanged even in the presence of an active attacker. We provide a vast literature overview of Wiretap Channels (WTCs) and channels with states and review the basic models in this area, such as Compound Channels (CCs), Discrete Memoryless Channels (DMCs) with random states, Arbitrarily Varying Channels (AVCs), Compound Wiretap Channels (CWCs), WTCs with random states, and the AVWCs. For these models, we provide an overview of the capacity results for different Channel State Information (CSI) scenarios, and the case that peak constraints are imposed on the input and state. If the active attacker has non-causal side information, situations in which a legitimate communication system has been hacked can be modeled. We investigate the AVWC with non-causal side information at the jammer for the case that there exists a best channel to the eavesdropper. Non-causal side information means that the transmitted codeword is known to an active adversary before it is transmitted. By considering the maximum error criterion, we also allow messages to be known at the jammer before the corresponding codeword is transmitted. A single-letter formula for the Common Randomness (CR)-assisted secrecy capacity is derived. We compare our results for different attacker and eavesdropping strengths. Secondly, we present a multi-letter expression for an achievable CR-assisted secrecy rate of an AVWC with input and state constraints. We can formulate statements about crucial properties of the AVWC, such as continuity or super additivity.