How To Build a Secret Chat App Using MLS and ChatE2EE
Designing a modern, end-to-end encrypted chat system for the web
Introduction
Building a secure chat application in 2026 is no longer just about
"encrypting messages."
Users expect:
- Strong end-to-end encryption (E2EE)
- Secure group messaging
- Dynamic member management
- Web-native performance
- Cryptographic correctness without UX pain
Traditional E2EE approaches don't scale well to groups.
This is why Messaging Layer Security (MLS) exists.
This article explains how a secret chat app using MLS + ChatE2EE was
designed and implemented in practice.
Why MLS Is Necessary
Problems With Traditional Group Encryption
- Pairwise encryption between every member
- O(n²) key management complexity
- Expensive re-keying
- High implementation risk
What MLS Solves
- Tree-based group key management
- Efficient member add/remove/update
- Forward secrecy & post-compromise security
- Formally verified cryptographic design
MLS is to group chat what TLS is to the web.
Overall Architecture
Technology Stack
Frontend
- TypeScript
- React
- Context-based state management
Cryptography
- OpenMLS
- Messaging Layer Security (RFC 9420)
- Rust → WebAssembly
Storage
- IndexedDB (web_sys)
- Hybrid memory + persistent cache
Core Chat Foundation
Chat Messaging Layer
- Message model
- Conversation abstraction
- Transport-agnostic pipeline
- Deterministic ordering
MLS handles encryption only --- not UX or transport.
WASM + OpenMLS Integration
- Rust bindings for JavaScript
- Minimal JS ↔ Rust surface
- Deterministic APIs
MLS Client Architecture
Group Lifecycle
- Group creation
- Welcome processing
- Member addition
- Secure state persistence
WASM Module Development
Why WASM
- Browser-safe cryptography
- Near-native performance
- Rust memory safety
- Reuse of OpenMLS
Runtime Responsibilities
- Encryption / decryption
- Group state transitions
- KeyPackage generation
- State serialization
Secure Key Storage
Hybrid Storage Strategy
Benefits: - Fast access - Crash recovery - Stable MLS epochs
Frontend Integration
Chat Context
- MLS initialization
- State restoration
- Message routing
- UI consistency
Message Flow
Security Guarantees
- End-to-end encryption
- Forward secrecy
- Post-compromise security
- Secure group membership
- Zero server plaintext
Lessons Learned
- MLS is complex but scalable
- Persistence bugs are catastrophic
- Welcome handling must be perfect
- Debugging encrypted state is hard
Conclusion
Building a secret chat app using MLS and ChatE2EE requires effort,
but the result is a future-proof, standards-based, highly secure
communication system.
MLS is not experimental.
MLS is production-ready.
Top comments (1)
Here is the Video how POC works