Security Capacity of Compound Wiretap Channel

Igor Bjelaković, Holger Boche, Jochen Sommerfeld

Holger Boche, Christian Deppe

We determine the identification capacity of compound channels in the presence of a wiretapper. It turns out that the secure identification capacity formula fulfills a dichotomy theorem: It is positive and equals the identification capacity of the channel if its message transmission secrecy capacity is positive. Otherwise, the secure identification capacity is zero. Thus, we show in the case that the secure identification capacity is greater than zero we do not pay a price for secure identification, i.e., the secure identification capacity is equal to the identification capacity. This is in strong contrast to the transmission capacity of the compound wiretap channel. We then use this characterization to investigate the analytic behavior of the secure identification capacity. In particular, it is practically relevant to investigate its continuity behavior as a function of the channels. We completely characterize this continuity behavior. We analyze the (dis-) continuity and (super-) additivity of the capacities. In 1998, N. Alon gave a conjecture about maximal violation for the additivity of capacity functions in graphs. We show that this maximal violation as well holds for the secure identification capacity of compound wiretap channels. This is the first example of a capacity function exhibiting this behavior.

Ziv Goldfeld, Paul Cuff, Haim Henri Permuter

Holger Boche, Rafael F. Schaefer, H. Vincent Poor

The wiretap channel models secure communication between two users in the presence of an eavesdropper who must be kept ignorant of transmitted messages. The performance of such a system is usually characterized by its secrecy capacity which determines the maximum transmission rate of secure communication. In this paper, the issue of whether or not the secrecy capacity is a continuous function of the system parameters is examined. In particular, this is done for channel uncertainty modeled via compound channels and arbitrarily varying channels, in which the legitimate users know only that the true channel realization is from a prespecified uncertainty set. In the former model, this realization remains constant for the entire duration of transmission, while in the latter the realization varies from channel use to channel use in an unknown and arbitrary manner. These models not only capture the case of channel uncertainty, but are also suitable for modeling scenarios in which a malicious adversary jams or otherwise influences the legitimate transmission. The secrecy capacity of the compound wiretap channel is shown to be robust in the sense that it is a continuous function of the uncertainty set. Thus, small variations in the uncertainty set lead to small variations in secrecy capacity. On the other hand, the deterministic secrecy capacity of the arbitrarily varying wiretap channel is shown to be discontinuous in the uncertainty set meaning that small variations can lead to dramatic losses in capacity.

Holger Boche, Rafael F. Schaefer, H. Vincent Poor

The performance of a secure communication system such as the wiretap channel is usually characterized by its secrecy capacity. In this paper, the issue of whether or not the secrecy capacity is a continuous function of the system parameters is examined. In particular, this is done for channel uncertainty modeled via compound channels and arbitrarily varying channels, in which the legitimate users know only that the true channel realization is from a pre-specified uncertainty set. In the former model, this realization remains constant for the entire duration of transmission, while in the latter the realization varies from channel use to channel use in an unknown and arbitrary manner. The secrecy capacity of the compound wiretap channel is shown to be robust in the sense that it is a continuous function of the uncertainty set. Thus, small variations in the uncertainty set lead to small variations in secrecy capacity. However, the secrecy capacity of the arbitrarily varying wiretap channel is shown to be discontinuous in the uncertainty set meaning that small variations can lead to dramatic losses in capacity.

S. Leung-Yan-Cheong