Covert Communications on Renewal Packet Channels

TL;DR

This paper extends the theory of covert communications to renewal packet channels, demonstrating limits on packet insertion and timing-based information transfer under different authentication scenarios.

Contribution

It introduces the information-theoretic limits for covert communication over renewal process-based packet channels, expanding beyond Poisson models to more general timing processes.

Findings

Alice can covertly insert O(√N) packets without detection.

Alice can reliably transmit O(N) bits using timing modifications.

The results apply to channels with non-Poisson renewal processes.

Abstract

Security and privacy are major concerns in modern communication networks. In recent years, the information theory of covert communications, where the very presence of the communication is undetectable to a watchful and determined adversary, has been of great interest. This emerging body of work has focused on additive white Gaussian noise (AWGN), discrete memoryless channels (DMCs), and optical channels. In contrast, our recent work introduced the information-theoretic limits for covert communications over packet channels whose packet timings are governed by a Poisson point process. However, actual network packet arrival times do not generally conform to the Poisson process assumption, and thus here we consider the extension of our work to timing channels characterized by more general renewal processes of rate $\lambda$. We consider two scenarios. In the first scenario, the source of the packets on the channel cannot be authenticated by Willie, and therefore Alice can insert packets into the channel. We show that if the total number of transmitted packets by Jack is $N$, Alice can covertly insert $\mathcal{O}\left(\sqrt{N}\right)$ packets and, if she transmits more, she will be detected by Willie. In the second scenario, packets are authenticated by Willie but we assume that Alice and Bob share a secret key; hence, Alice alters the timings of the packets according to a pre-shared codebook with Bob to send information to him over a $G/M/1$ queue with service rate $\mu>\lambda$. We show that Alice can covertly and reliably transmit $\mathcal{O}(N)$ bits to Bob when the total number of packets sent from Jack to Steve is $N$.