What is Messaging Layer Security (MLS)?

Messaging Layer Security (MLS) is the IETF's open standard — published as RFC 9420 — for end-to-end encrypted group communication. Classic E2EE protocols were designed around pairwise conversations; extending them to groups historically meant either encrypting every message separately to every member (which scales poorly) or sharing a single static group key (which weakens forward secrecy and complicates membership changes). MLS solves the group problem directly: members share a cryptographic tree structure that lets the group agree keys efficiently, add and remove members with fresh keys per change (so a removed member cannot read future messages, and a new member cannot read past ones), and heal from device compromise through continuous key updates. The properties that matter to an enterprise evaluator: it is an open standard with public specification and academic scrutiny rather than a proprietary design; it scales group [end-to-end encryption](/glossary/end-to-end-encryption) to organisational sizes — departments, sites, whole-company announcement structures; and its membership-change semantics map naturally onto organisational lifecycle, where joiners, movers, and leavers are directory events that should have cryptographic consequences. For buyers of [secure enterprise messaging](/glossary/secure-enterprise-messaging), MLS alignment is a reasonable line item on the requirements list: it signals the vendor builds on scrutinised standards, and it future-proofs the platform as the standard's ecosystem matures. Zeour's NOVARYX platform aligns its group encryption design with MLS, combined with per-sender message signing so that even inside an encrypted group, one member cannot impersonate another.