Secret Key Establishment over a Pair of Independent Broadcast Channels

TL;DR

This paper investigates the fundamental limits of secret key establishment over two independent broadcast channels in opposite directions, providing capacity bounds and a practical protocol for secure communication.

Contribution

It introduces the secret-key capacity for the 2DMBC setup and derives matching bounds, including a two-round protocol with a novel coding scheme.

Findings

Lower and upper bounds on secret-key capacity are established.

The bounds coincide for degraded broadcast channels.

A two-round protocol achieves the lower bound.

Abstract

This paper considers the problem of information-theoretic Secret Key Establishment (SKE) in the presence of a passive adversary, Eve, when Alice and Bob are connected by a pair of independent discrete memoryless broadcast channels in opposite directions. We refer to this setup as 2DMBC. We define the secret-key capacity in the 2DMBC setup and prove lower and upper bounds on this capacity. The lower bound is achieved by a two-round SKE protocol that uses a two-level coding construction. We show that the lower and the upper bounds coincide in the case of degraded DMBCs.