Consistency Protocols for Transparency Technologies

Research Project, 2025 – 2030

A central problem in reliable systems is achieving consensus despite malfunctioning components.This problem, known as Byzantine fault-tolerant (BFT) agreement, is often formulated as a set of Lieutenants who should agree on an order from the Commander.Existing solutions rely on either peer-to-peer direct and authenticated channels among all parties (a complete network graph), or broadcast (recently implemented as blockchains). This project explores a new setting for the BFT agreement problem: a star topology with the Commander being the central node. This setting poses unique challenges due to the absence of peer-to-peer channels among Lieutenants, broadcast channels, and guaranteed output delivery.Specifically, this project investigates consistency protocols, namely epoch-based BFT agreement protocols in the star topology with a very large number of Byzantine Lieutenants and one malicious Commander.This setting models a centralized Public Key Infrastructure (PKI) that distribute users´ public keys in modern digital systems such as end-to-end encrypted messaging apps, and privacy-preserving location-based services.This project defines and investigates evolving committee-based consistency protocols, a novel branch of consistency protocols for Transparency Logs (a generalization of a verifiable PKI). The goal is to prove security against a set of powerful and realistic adversaries using advanced cryptographic schemes and results from probability theory.