Signal and Messaging Layer Security is a comprehensive guide to signal protocol. Used by widely deployed messengers such as Facebook Messenger, WhatsApp, Wire, Viber, and many others, Signal has become the standard for end-to-end encrypted (E2EE) communication. Despite its widespread adoption, the protocol remains largely unexplained in security literature. This book fills that gap by providing a clear, accessible explanation of the Signal protocol for security professionals with a basic understanding of cryptography.
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 group settings making it an essential resource for anyone working in the field of secure communications.
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
About the Author :
Rolf Oppliger Rolf Oppliger leads eSECURITY Technologies, works for the Swiss federal administration, serves as an adjunct professor of computer science at the University of Z, rich, Switzerland, and is the Information Security and Privacy editor at Artech House. He earned his Ph.D. in computer science from the University of Berne, Switzerland.
