Amigo: Secure Group Mesh Messaging in Realistic Protest Settings

During large-scale protests, a repressive government will often disable the Internet to thwart communication between protesters. Smartphone mesh networks, which route messages over short-range, possibly ephemeral, radio connections between nearby phones, allow protesters to communicate without relying on centralized Internet infrastructure. Unfortunately, prior work on providing secure communication in Internet shutdown settings fails to adequately consider protester needs. Previous attempts fail to support efficient private group communication (a crucial requirement for protests), and evaluate their solutions in network environments which fail to accurately capture link churn, physical spectrum contention, and the mobility models found in realistic protest settings. In this paper, we introduce Amigo, a novel mesh messaging system which supports group communication through a decentralized approach to continuous key agreement, and forwards messages using a novel routing protocol. Amigo is uniquely designed to handle the challenges of ad-hoc routing scenarios, where dynamic network topologies and node mobility make achieving key agreement nontrivial. Our extensive simulations reveal the poor scalability of prior approaches, the benefits of Amigo's protest-specific optimizations, and the challenges that still must be solved to scale secure mesh networks to protests with thousands of participants.