Covert Bits Through Queues

TL;DR

This paper explores covert communication over queuing timing channels, demonstrating that with a high-rate secret key, non-zero covert rates are achievable, unlike traditional channels limited to very few covert bits.

Contribution

It introduces schemes for covert communication via queues that achieve positive rates with sufficient secret key, contrasting with classical models limited to square-root law.

Findings

Achieves non-zero covert rates with high-rate secret keys.

Contrasts queuing channels with Gaussian and DMC models.

Provides achievable schemes for exponential and general queues.

Abstract

We consider covert communication using a queuing timing channel in the presence of a warden. The covert message is encoded using the inter-arrival times of the packets, and the legitimate receiver and the warden observe the inter-departure times of the packets from their respective queues. The transmitter and the legitimate receiver also share a secret key to facilitate covert communication. We propose achievable schemes that obtain non-zero covert rate for both exponential and general queues when a sufficiently high rate secret key is available. This is in contrast to other channel models such as the Gaussian channel or the discrete memoryless channel where only $\mathcal{O}(\sqrt{n})$ covert bits can be sent over $n$ channel uses, yielding a zero covert rate.