FoSAM: Forward Secret Messaging in Ad-Hoc Networks

TL;DR

FoSAM is a novel protocol enabling anonymous, forward secret messaging in unreliable ad-hoc networks, enhancing privacy and security for users in restricted environments.

Contribution

FoSAM introduces the first protocol to provide proven anonymous and forward secret messaging without requiring interactive handshakes in ad-hoc networks.

Findings

Achieves 92%-99% message delivery success in simulations.

Requires only receiver's public key for communication.

Prototype implementation on Android demonstrates practicality.

Abstract

Apps such as Firechat and Bridgefy have been used during recent protests in Hong Kong and Iran, as they allow communication over ad-hoc wireless networks even when internet access is restricted. However, these apps do not provide sufficient protection as they do not achieve forward secrecy in unreliable networks. Without forward secrecy, caught protesters' devices will disclose all previous messages to the authorities, putting them and others at great risk. In this paper, we introduce FoSAM, the first protocol to provide proven anonymous and forward secret messaging in unreliable ad-hoc networks. Communication in FoSAM requires only the receiver's public key, rather than an interactive handshake. We evaluate the performance of FoSAM using a large-scale simulation with different user movement patterns, showing that it achieves between 92% and 99% successful message delivery. We additionally implement a FoSAM prototype for Android.