Post‑Quantum Secure Messaging System
MSc dissertation project exploring a post‑quantum secure messaging system designed to address the emerging threat of “Harvest Now, Decrypt Later” (HNDL) attacks in end-to-end encrypted communication.
Overview
With the rise of quantum computing, long-term encrypted communications face increasing risk from adversaries who may capture encrypted data today and decrypt it in the future once quantum-capable systems become available. This project investigates how modern messaging systems can transition toward post‑quantum cryptography (PQC) while preserving the core security guarantees expected from secure messaging platforms:
- Confidentiality
- Authentication
- Forward Secrecy
- Post‑Compromise Security
- Non‑Repudiation
Research Focus
The project studied the cryptographic foundations of secure messaging systems, with particular attention to the Signal protocol and its supporting mechanisms such as:
- X3DH
- PQXDH
- Double Ratchet
While much existing work focuses on Signal-based applications such as Signal, WhatsApp, Wire, Facebook Messenger and similar platforms, this dissertation identified a research and implementation gap in relation to Keybase, an end-to-end encrypted messaging, identity verification, and file-sharing system.
Key Contributions
This dissertation proposes and evaluates a hybrid post‑quantum secure messaging approach within the Keybase application architecture by combining:
- Post‑quantum SC-AKE (Signal-Conforming Authenticated Key Exchange)
- Symmetric signcryption
- CRYSTALS-Kyber for key establishment
- CRYSTALS-Dilithium for digital signatures
The resulting proof-of-concept application demonstrates how post‑quantum techniques can be integrated into practical secure messaging workflows, bridging the gap between theoretical cryptographic advances and real-world implementation.
Highlights
- Designed a hybrid post‑quantum messaging framework for secure end-to-end communication.
- Implemented post‑quantum cryptographic primitives using Kyber and Dilithium.
- Explored the adaptation of Signal-conforming authenticated key exchange to a non-Signal messaging architecture.
- Investigated how PQC can preserve key messaging properties such as forward secrecy and post-compromise security.
- Built a proof-of-concept application to evaluate feasibility in a realistic operational setting.
- Examined the often-overlooked role of digital signatures in long-term conversational authenticity and trust.
Outcome
The project demonstrates that post‑quantum secure messaging is not just a theoretical concern, but a practical systems engineering challenge. The proof-of-concept establishes a foundation for extending Keybase-like identity verification and messaging systems to resist future PQC threats, while also highlighting the importance of securing both key exchange and digital signatures in next-generation encrypted communication.
Repository
The complete implementation, documentation, automation, manifests, policies, tests, and definitions are available on GitHub:
View the message-cli repository
Technologies / Concepts
Post-Quantum Cryptography · CRYSTALS-Kyber · CRYSTALS-Dilithium · Signal Protocol · SC-AKE · Signcryption · End-to-End Encryption · Keybase · Secure Messaging · Quantum-Safe Security