In this work, a class of information theoretic secrecy problems is addressedwhere the eavesdropper channel states are completely unknown to the legitimateparties. In particular, MIMO wiretap channel models are considered where thechannel of the eavesdropper is arbitrarily varying over time. Assuming that thenumber of antennas of the eavesdropper is limited, the secrecy rate of the MIMOwiretap channel in the sense of strong secrecy is derived, and shown to matchwith the converse in secure degrees of freedom. It is proved that there existsa universal coding scheme that secures the confidential message against anysequence of channel states experienced by the eavesdropper. This yields theconclusion that secure communication is possible regardless of the location orchannel states of (potentially infinite number of) eavesdroppers. Additionally,it is observed that, the present setting renders the secrecy capacity problemsfor multi-terminal wiretap-type channels more tractable as compared the casewith full or partial knowledge of eavesdropper channel states. To demonstratethis observation, secure degrees of freedom regions are derived for theGaussian MIMO multiple access wiretap channel (MIMO MAC-WT) and the GaussianMIMO broadcast wiretap channel (MIMO BC-WT) where the transmitter(s) and theintended receiver(s) have the same number of antennas.
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