Secret Communication Under Channel Uncertainty

Mark M. Wilde, Joseph M. Renes

We construct a new secret-key assisted polar coding scheme for private classical communication over a quantum or classical wiretap channel. The security of our scheme rests on an entropic uncertainty relation, in addition to the channel polarization effect. Our scheme achieves the symmetric private information rate by synthesizing "amplitude" and "phase" channels from an arbitrary quantum wiretap channel. We find that the secret-key consumption rate of the scheme vanishes for an arbitrary degradable quantum wiretap channel. Furthermore, we provide an additional sufficient condition for when the secret key rate vanishes, and we suspect that satisfying this condition implies that the scheme requires no secret key at all. Thus, this latter condition addresses an open question from the Mahdavifar-Vardy scheme for polar coding over a classical wiretap channel.

Hien Quang Ta, Quoc‐Viet Pham, Khuong Ho‐Van +1 more

Kyatsandra G. Nagananda

Masahito Hayashi, M. A. Vázquez‐Castro

We propose a covert communication protocol for the spread-spectrum multiple random access with additive white Gaussian noise (AWGN) channel. No existing paper has studied covert communication for the random access channel. Our protocol assumes binary discrete phase-shift keying (BPSK) modulation, and it works well under imperfect channel state information (I-CSI) for both the legitimate and adversary receivers, which is a realistic assumption in the low power regime. Also, our method assumes that the legitimate users share secret variables in a similar way as the preceding studies. Although several studies investigated the covert communication for the point-to-point communication, no existing paper considers the covert communication under the above uncertainty assumption even for point-to-point communication. Our protocol under the above uncertainty assumption allowsO(n) legitimate senders andO(n/logn) active legitimate senders. Furthermore, our protocol can be converted to a protocol for point-to-point communication that works under the above uncertainty assumption.

Abdalla Ibrahim, Johannes Rosenberger, Boulat A. Bash +2 more

Hassan ZivariFard, Matthieu R. Bloch, Aria Nosratinia

We consider the problem of covert communication over a state-dependent channel, for which the transmitter and the legitimate receiver have non-causal access to the channel state information. Covert communication with respect to an adversary, referred to as the “warden,” is one in which the distribution induced during communication at the channel output observed by the warden is identical to the output distribution conditioned on an inactive channel-input symbol. Covert communication involves fooling an adversary in part by a proliferation of codebooks; for reliable decoding at the legitimate receiver the codebook uncertainty is removed via a shared secret key that is unavailable to the warden. Unlike earlier work in state-dependent covert communication, we do not assume the availability of a shared key at the transmitter and legitimate receiver. Rather, a shared randomness is extracted at the transmitter and the receiver from the channel state, in a manner that keeps the shared randomness secret from the warden despite the influence of the channel state on the warden's output. An inner bound on the covert capacity, in the absence of an externally provided secret key, is derived.