How Group Encrypted Messaging Actually Works

Secure group messaging has evolved from pairwise encryption to Sender Keys and now MLS to balance security with scale.

Pairwise encryption is strong but becomes inefficient as group size grows because every message must be sent individually.

Signal’s Sender Keys cut per-message overhead, but they trade off some post-compromise recovery after a key leak.

MLS (Messaging Layer Security, RFC 9420) uses a tree-based design to handle joins and leaves efficiently while preserving stronger security guarantees.