[Paper Review] Reliable, Deniable, and Hidable Communication over Multipath Networks

Swanand Kadhe, Sidharth Jaggi+2 more|arXiv (Cornell University)|Jan 17, 2014

Wireless Communication Security Techniques10 references6 citations

TL;DR

This paper proposes a communication protocol for reliable, deniable, and hidable transmission over multipath networks, where Alice sends covert messages to Bob while evading detection by a passive eavesdropper Willie. Using random binning and stochastic encoding over multiple parallel links, the scheme achieves both deniability (Willie cannot detect transmission) and hidability (Willie gains no information about the message), with matching inner and outer bounds establishing the capacity for such communication.

ABSTRACT

We consider the scenario wherein Alice wants to (potentially) communicate to the intended receiver Bob over a network consisting of multiple parallel links in the presence of a passive eavesdropper Willie, who observes an unknown subset of links. A primary goal of our communication protocol is to make the communication "deniable", {\it i.e.}, Willie should not be able to {\it reliably} estimate whether or not Alice is transmitting any {\it covert} information to Bob. Moreover, if Alice is indeed actively communicating, her covert messages should be information-theoretically "hidable" in the sense that Willie's observations should not {\it leak any information} about Alice's (potential) message to Bob -- our notion of hidability is slightly stronger than the notion of information-theoretic strong secrecy well-studied in the literature, and may be of independent interest. It can be shown that deniability does not imply either hidability or (weak or strong) information-theoretic secrecy; nor does any form of information-theoretic secrecy imply deniability. We present matching inner and outer bounds on the capacity for deniable and hidable communication over {\it multipath networks}.

Motivation & Objective

• To design a communication protocol that ensures reliable delivery from Alice to Bob in the presence of a passive eavesdropper Willie.
• To achieve deniability, such that Willie cannot reliably determine whether Alice is transmitting any information.
• To ensure hidability, meaning Willie gains no information about Alice’s covert messages, even if he detects transmission.
• To formalize and characterize the capacity limits for reliable, deniable, and hidable communication over multipath networks.
• To demonstrate that deniability and hidability are independent properties, neither implying the other.

Proposed method

• Formalizes a multipath network model with multiple parallel links, where Willie observes a random subset of links.
• Introduces a hypothesis testing-based metric for deniability, ensuring Willie cannot distinguish between innocent and active communication.
• Employs random binning to generate codebooks and a one-to-many stochastic mapping for encoding covert messages.
• Uses strong typicality and type-based analysis to bound error probabilities and ensure reliability.
• Applies information-theoretic tools, including variation distance and entropy bounds, to analyze deniability and hidability.
• Derives matching inner and outer bounds on capacity by analyzing the behavior of typical sequences and binning under Willie’s partial observation.

Experimental results

Research questions

• RQ1 What is the fundamental capacity limit for reliable, deniable, and hidable communication over multipath networks with a passive eavesdropper?
• RQ2 Can deniability and hidability coexist in a communication protocol, and if so, under what conditions?
• RQ3 How does the capacity for deniable communication compare to that for hidable communication, and are they equivalent?
• RQ4 Can a single protocol achieve both deniability and hidability simultaneously, and what encoding strategies enable this?
• RQ5 Is there a separation between deniability and information-theoretic secrecy, and how does hidability differ from strong secrecy?

Key findings

• The paper establishes matching inner and outer bounds on the capacity for reliable, deniable, and hidable communication over multipath networks.
• The reliable-deniable capacity is characterized and shown to be achievable using random binning and stochastic encoding.
• The reliable-deniable-hidable capacity is also characterized, with the same stochastic encoding scheme achieving optimal performance.
• Hidability is shown to be strictly stronger than strong information-theoretic secrecy, as it requires the mutual information between Willie’s observation and the message to be zero.
• The analysis proves that deniability and hidability are independent: neither implies the other, and both can be achieved simultaneously with proper protocol design.
• The probability of Willie correctly detecting transmission tends to zero as the blocklength increases, provided the rate is below the derived capacity limit.