The Ephemeral Pairing Problem

TL;DR

This paper introduces the ephemeral pairing problem in wireless networks, focusing on establishing short-term shared secrets through low-bandwidth channels, and presents several protocols for different channel types.

Contribution

It formalizes the ephemeral pairing problem and proposes multiple key exchange protocols tailored for authentic and private communication channels.

Findings

Protocols successfully establish shared secrets without prior information.

Protocols work over low-bandwidth authentic and private channels.

The approach enables ephemeral secure connections in ad-hoc networks.

Abstract

In wireless ad-hoc broadcast networks the pairing problem consists of establishing a (long-term) connection between two specific physical nodes in the network that do not yet know each other. We focus on the ephemeral version of this problem. Ephemeral pairings occur, for example, when electronic business cards are exchanged between two people that meet, or when one pays at a check-out using a wireless wallet. This problem can, in more abstract terms, be phrased as an ephemeral key exchange problem: given a low bandwidth authentic (or private) communication channel between two nodes, and a high bandwidth broadcast channel, can we establish a high-entropy shared secret session key between the two nodes without relying on any a priori shared secret information. Apart from introducing this new problem, we present several ephemeral key exchange protocols, both for the case of authentic channels as well as for the case of private channels.