Secret-Key Generation using Correlated Sources and Channels

TL;DR

This paper investigates the maximum rate at which two terminals can generate a shared secret key using correlated sources and a wiretap channel, establishing capacity bounds and optimal strategies in various scenarios including Gaussian channels and degraded sources.

Contribution

It derives the secret-key capacity bounds for joint source-channel setups, including cases with multiple eavesdropper observations and public discussion channels, and identifies optimal coding strategies.

Findings

Capacity bounds are tight for independent, parallel, and reversely degraded channels.

Gaussian codebooks achieve capacity in the Gaussian case.

Separate key generation from source and channel components is optimal under certain conditions.

Abstract

We study the problem of generating a shared secret key between two terminals in a joint source-channel setup -- the sender communicates to the receiver over a discrete memoryless wiretap channel and additionally the terminals have access to correlated discrete memoryless source sequences. We establish lower and upper bounds on the secret-key capacity. These bounds coincide, establishing the capacity, when the underlying channel consists of independent, parallel and reversely degraded wiretap channels. In the lower bound, the equivocation terms of the source and channel components are functionally additive. The secret-key rate is maximized by optimally balancing the the source and channel contributions. This tradeoff is illustrated in detail for the Gaussian case where it is also shown that Gaussian codebooks achieve the capacity. When the eavesdropper also observes a source sequence, the secret-key capacity is established when the sources and channels of the eavesdropper are a degraded version of the legitimate receiver. Finally the case when the terminals also have access to a public discussion channel is studied. We propose generating separate keys from the source and channel components and establish the optimality of this approach when the when the channel outputs of the receiver and the eavesdropper are conditionally independent given the input.