Description
Signal and Messaging Layer Security is an in-depth resource to understanding the Signal protocol, a cornerstone of modern secure communication. Used by globally popular messaging platforms such as Facebook Messenger, WhatsApp, Wire, Viber, and a host of others, Signal has become the gold standard for end-to-end encrypted (E2EE) messaging. Despite its widespread use, the intricate details of the protocol have largely remained underexplored in mainstream security literature. This book bridges that knowledge gap by offering a clear, structured, and accessible explanation of the Signal protocol. Aimed at security professionals who possess a foundational understanding of cryptography, it delves into the inner workings of the protocol, breaking down complex concepts and providing practical insights to enhance security expertise.
Beyond the Signal protocol, the book also addresses the crucial challenge of scaling E2EE messaging to group communication. While Signal was designed for two-party messaging, extending its security guarantees to large groups is a complex problem. The second focus of this book is the Messaging Layer Security (MLS) protocol, currently being standardized by the Internet Engineering Task Force (IETF.) MLS is designed for large-scale deployments, enabling secure group messaging for thousands of participants.
By exploring both Signal and MLS, this book offers a deep dive into the protocols shaping secure communication today. It provides a clear and comprehensive guide to understanding the core principles behind modern E2EE messaging. Readers will gain an understanding of forward secrecy, post-compromise security, and the intricacies of encrypted messaging in both one-on-one and gro
Table Of Contents
Chapter 1 Introduction
1.1 Problem Statement
1.2 Historical Summary
1.3 Book Outline
Chapter 2 Cryptographic Toolbox
2.1 Unkeyed Cryptosystems
2.2 Secret Key Cryptosystems
2.3 Public Key Cryptosystems
2.4 Final Remarks
Chapter 3 Evolution
3.1 Phase 1: First Solutions
3.2 Phase 2: Synchronous Messaging
3.3 Phase 3: Asynchronous Messaging
3.4 Phase 4: Group Messaging
3.5 Final Remarks
Chapter 4 Signal Protocol
4.1 Introduction
4.2 X3DH
4.3 PQXDH
4.4 Double Ratchet Mechanism
4.5 User Authentication
4.6 Security Analysis
4.7 Final Remarks
Chapter 5 Group Communication
5.1 Introduction
5.2 Signal Protocol in Groups
5.3 Sender Keys
5.4 More Efficient Technologies and Protocols
5.5 Final Remarks
Chapter 6 MLS Protocol
6.1 Introduction
6.2 Architectural Setting
6.3 Protocol
6.4 Security Analysis
6.5 Final Remarks
Chapter 7 Further Developments and Improvements
7.1 Multi-Device Support
7.2 Cloud Storage
7.3 Self-Destructing Messages
7.4 Private Groups
7.5 Message Franking
7.6 Meta-Data Hiding
Chapter 8 Conclusions and Outlook
Chapter A ECC
Chapter B Quantum Computers and PQC
B.1 Quantum Computers
B.2 PQC
Chapter C Mathematical Notation
Chapter D Abbreviations and Acronyms
About the Author