Keyless Covert Communication via Channel State Information

TL;DR

This paper investigates how to achieve covert communication over state-dependent channels without shared keys by extracting secrecy from channel state information, deriving capacity regions and bounds.

Contribution

It introduces a novel approach to covert communication that does not rely on shared keys but uses channel state information to ensure secrecy from an adversary.

Findings

Derived the covert capacity region with channel state at both transmitter and receiver.

Established inner and outer bounds for covert capacity with channel state only at the transmitter.

Demonstrated scenarios where covert capacity is positive with state information but zero without it.

Abstract

We consider the problem of covert communication over a state-dependent channel when the channel state is available either non-causally, causally, or strictly causally, either at the transmitter alone or at both transmitter and receiver. Covert communication with respect to an adversary, called "warden," is one in which, despite communication over the channel, the warden's observation remains indistinguishable from an output induced by innocent channel-input symbols. Covert communication involves fooling an adversary in part by a proliferation of codebooks; for reliable decoding at the legitimate receiver, the codebook uncertainty is typically removed via a shared secret key that is unavailable to the warden. In contrast to previous work, we do not assume the availability of a shared key at the transmitter and legitimate receiver. Instead, shared randomness is extracted from the channel state in a manner that keeps it secret from the warden, despite the influence of the channel state on the warden's output. When channel state is available at the transmitter and receiver, we derive the covert capacity region. When channel state is only available at the transmitter, we derive inner and outer bounds on the covert capacity. We provide examples for which the covert capacity is positive with knowledge of channel state information but is zero without it.