MLS (Messaging Layer Security)
P2P Protocol
Community
Details
License Open specification (IETF, no licence fee; RFC text under IETF Trust terms). Independent open-source implementations: OpenMLS (Rust, MIT/Apache-2.0), MLS++ (C++, from Cisco)
Dev Status 🏁 Final
Owner IETF — Messaging Layer Security (MLS) Working Group. RFC 9420 authors: Richard Barnes, Benjamin Beurdouche, Raphael Robert, Jon Millican, Emad Omara, Katriel Cohn-Gordon. Contributors include Cisco, Mozilla, Wire, Meta, Google and academic cryptographers
Owner - List
- Internet Engineering Task Force
Governing Body IETF (Messaging Layer Security Working Group)
Country International (IETF process; contributing organizations span the USA, France, Germany and the UK)
Start Year 2018
Stack Language-agnostic specification. Reference and production implementations in Rust (OpenMLS) and C++ (MLS++); bindings widely available
Funding Open standards process — participant organizations fund their own contributors; no central budget
Last Investigated Jul 31, 2026
P2P Protocol Attributes
Owner - List
- Internet Engineering Task Force
Origins Secure messaging / cryptography — motivated by the fact that pairwise ratchets such as Signal's Double Ratchet scale poorly to large groups, and that every major messenger had built its own incompatible group-encryption scheme. MLS was chartered to produce one interoperable, formally analysed standard
Database N/A — a security protocol; group state is held by clients. No storage layer defined
Query Language N/A — no query interface
Data Formats MLS wire formats defined in RFC 9420: MLSMessage, KeyPackage, Welcome, Commit, Proposal, GroupInfo and the ratchet tree encoding. Ciphersuites cover X25519/Ed25519, P-256/P-384/P-521 and X448 with AES-GCM or ChaCha20-Poly1305
Collaborative Live Editing N/A — a security layer, not an editing protocol; it can secure the transport of collaborative traffic but defines nothing about it
Rich Text Editing N/A — content-agnostic; MLS protects opaque application messages
Mobile Support Library-level — implementations are embedded in mobile messaging clients; no standalone application
Web Support Library-level — implementations compile to WebAssembly and are used in browser clients; the protocol itself is transport-independent
Native Apps Library-level — embedded in native messaging clients
Terms Free / open standard — no licensing fees; RFC freely published
Funds N/A — IETF working groups are not separately funded entities
Based On IETF cryptographic primitives (HPKE RFC 9180, HKDF, AEAD ciphers, Ed25519/ECDSA signatures); TreeKEM (ratcheting binary key tree, the protocol's core construction); builds conceptually on the Double Ratchet lineage while replacing its pairwise scaling model
P2P Architecture Transport-agnostic by design — MLS specifies no routing or peer discovery. It assumes an external Delivery Service responsible for message ordering and fan-out, which may be a centralized server, a federated network, or a decentralized relay network. This is precisely why it can be layered onto Nostr (Marmot Protocol), onto federated networks, or onto peer-to-peer transports
Overlay Network N/A — defined at the group level rather than the network level; group membership is the only topology MLS defines
Content Addressing No — messages are identified within group epochs, not by content hash
Local-First N/A — MLS requires ordered delivery of handshake messages, so group state advances only as commits are received. It is not offline-first in the CRDT sense, though message protection is fully client-side
E2EE Yes — this is the protocol's entire purpose: end-to-end encryption with forward secrecy and post-compromise security. The Delivery Service sees ciphertext and metadata but never plaintext or group secrets
CRDTs Lib N/A — MLS requires a total order on handshake messages and does not use CRDTs
Byzantine Fault Tolerance No — MLS assumes an honest-but-curious Delivery Service for liveness and does not provide consensus. It protects confidentiality and integrity against a malicious server, but a malicious Delivery Service can withhold or reorder messages
Signature Ed25519, ECDSA (P-256/P-384/P-521) depending on ciphersuite; credentials bind signature keys to identities via the external Authentication Service
Permissions Group membership and roles — Add, Update and Remove proposals committed by group members; the specification defines the mechanism and leaves authorization policy to the application
Semantic Web Compatibility N/A — binary wire protocol with no semantic layer
Smart Contract N/A — no ledger or contract component
Protocol Stack Position Application-layer (built on TCP/IP) — sits above transport and below the messaging application; deliberately independent of the underlying network
Asset / Value Embedding None — no token, ledger, or value-transfer mechanism
Protocol Maturity / Standardization IETF Proposed Standard — RFC 9420, published July 2023, with multiple independent interoperable implementations and formal security analysis conducted during standardisation. Among the most mature entries in this file
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