ABSTRACT
Physical layer security, also called information theoretic security, is an emerging field which exploits physical layer properties of communication channels to secure future generations of communication systems. The approach to generating the secret key at the physical layer is proposed in the source model by the pioneer works. Different from the key generation process in the source model, the legitimate users typically observe no sources in advance, but they can obtain the sources via estimating the channel gain. This chapter discusses the problem of key generation under active attacks. It first reviews the basic scenarios for key generation in the presence of a passive adversary. Then, it considers the scenario where the attacker attacks the public discussion, reviews the relationship between the key rate obtained from the case with an active attacker with the corresponding key rate obtained from the passive case and discusses the condition which decides this relationship.
