MLS Group Messaging: How Zero-Knowledge Can Secure Updates

The Messaging Layer Security (MLS) protocol currently developed by the Internet Engineering Task Force (IETF) aims at providing a secure group messaging solution. MLS aims for end-to-end security, including Forward Secrecy and Post Compromise Secrecy, properties well studied for one-to-one protocols. It proposes a tree-based regular asynchronous update of the group secrets, where a single user can alone perform a complete update. A main drawback is that a malicious user can create a denial of service attack by sending invalid update information.