Secrecy and covertness in the presence of multi-casting, channel state information, and cooperative jamming




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We study secret communication over multi-transmitter multicast problem in the presence of an eavesdropper, wherein weak and strong secrecy regimes are studied. For the weak secrecy regime, the method of Chia and El Gamal is extended to two transmitters. We show that the achievable region calculated for the weak secrecy regime in this channel configuration is no bigger than the one calculated under strong secrecy. Two examples are presented in which the inner and outer bounds of secrecy region meet. In the process, we also characterize the minimum amount of randomness necessary to achieve secrecy in the multiple-access wiretap channel. We consider the problem of covert communication over a state-dependent channel when the Channel State Information (CSI) is available either non-causally, causally, or strictly causally, either at the transmitter alone, or at both transmitter and receiver. In contrast to previous work, we do not assume the availability of a large shared key at the transmitter and legitimate receiver. Instead, we only require a secret key with negligible rate to bootstrap the communication and our scheme extracts shared randomness from the CSI in a manner that keeps it secret from the warden, despite the influence of the CSI on the warden’s output. When CSI is available at the transmitter and receiver, we derive the covert capacity region. When CSI is only available at the transmitter, we derive inner and outer bounds on the covert capacity. We also provide examples for which the covert capacity is positive with knowledge of CSI but is zero without it. We consider the problem of covert communication in the presence of a cooperative jammer. It is known that in general, a transmitter and a receiver can communicate only O( √ n) covert bits over n channel uses, i.e., zero rate. Here, we show that a cooperative jammer can facilitate the communication of positive covert rates, subject to the presence of friendly jammer in the environment. We consider various scenarios in which it is possible to achieve positive rate for covert communication. For these scenarios, we derive inner and outer bounds on the covert capacity region, and also we characterize the covert capacity region for some of these scenarios.



Engineering, Electronics and Electrical, Computer Science