Messaging Layer Security

Short description: Messaging protocol

Messaging Layer SecurityProtocol stack

Purpose| End-to-end encrypting messages
Developer(s)|

* Richard Barnes
* Benjamin Beurdouche
* Raphael Robert
* Jon Millican
* Emad Omara
* Katriel Cohn-Gordon

Introduced| July 2023; 3 years ago (2023-07)
OSI layer| Application layer
RFC(s)| 9420

Messaging Layer Security (MLS) is a security layer for end-to-end encrypted messages. It is maintained by the MLS working group of the Internet Engineering Task Force (IETF), and is designed to provide an efficient and practical security mechanism for groups as large as 50,000 and for those who access chat systems from multiple devices.[1][2][3]

## Contents

* 1 Security properties
* 2 History
* 3 Implementations
* 4 References
* 5 External links

## Security properties

Security properties of MLS include message confidentiality, message integrity and authentication, membership authentication, asynchronicity, forward secrecy, post-compromise security, and scalability.[4]

## History

The idea was born in 2016 and first discussed in an unofficial meeting during IETF 96 in Berlin with attendees from Wire, Mozilla and Cisco.[5]

Initial ideas were based on pairwise encryption for secure 1:1 and group communication. In 2017, an academic paper introducing Asynchronous Ratcheting Trees was published by the University of Oxford and Facebook setting the focus on more efficient encryption schemes.[6]

The first BoF took place in February 2018 at IETF 101 in London. The founding members are Mozilla, Facebook, Wire, Google, Twitter, University of Oxford, and INRIA.[7]

On March 29, 2023, the IETF approved publication of Messaging Layer Security (MLS) as a new standard.[8] It was officially published on July 19, 2023.[9][10] At that time, Google announced it intended to add MLS to the end to end encryption used by Google Messages over Rich Communication Services (RCS).[11] In March 2025, the GSMA announced the Universal Profile 3.0 standard of RCS would support MLS and Apple announced it would support this RCS standard on Apple Messages.[12][13] Both Google Messages and Apple Messages began the rollout of MLS E2EE over RCS in May 2026.[14][15]

Matrix is one of the protocols declaring migration to MLS.[16]

In 2026, Discord rolled out end-to-end encryption on voice and video calls, using MLS for scalable group key exchanges.[17]

Research on adding post-quantum cryptography (PQC) to MLS is ongoing.[18][19][20] The IETF has prepared an Internet-Draft using PQC algorithms in MLS.[21]

## Implementations

MLS implementations  Implementation | Language | License | Developer

|
|
|

OpenMLS | Rust | MIT | Phoenix R&D and Cryspen
MLS++ | C++ | BSD 2-Clause | Cisco
mls-rs | Rust | Apache 2.0 | AWS Labs
MLS-TS | TypeScript | Apache 2.0 | Matrix Foundation
xmtp_mls | Rust  | MIT  | XMTP Labs

## References

1. ↑ "Inside MLS, the New Protocol for Secure Enterprise Messaging" (in en). 27 June 2019. https://www.darkreading.com/perimeter/inside-mls-the-new-protocol-for-secure-enterprise-messaging/d/d-id/1335075.
2. ↑ at 10:29, Richard Chirgwin 22 Aug 2018. "Elders of internet hash out standards to grant encrypted message security for world+dog" (in en). https://www.theregister.co.uk/2018/08/22/ietf_draft_proposes_encrypted_message_security_for_all/.
3. ↑ "Messaging Layer Security". https://mlswg.github.io.
4. ↑ "Messaging Layer Security (mls) -". https://datatracker.ietf.org/wg/mls/about/.
5. ↑ "Das sind die sieben Entwickler-Trends 2019: Vom Java-Comeback über MLS bis KI/ML-zentrierte Technologien". 2 January 2019. https://www.it-finanzmagazin.de/sieben-entwickler-trends-2019-83043/. Retrieved 7 January 2019.
6. ↑ Cohn-Gordon, Katriel; Cremers, Cas; Garratt, Luke; Millican, Jon; Milner, Kevin (2017). "On Ends-to-Ends Encryption: Asynchronous Group Messaging with Strong Security Guarantees". Cryptology ePrint Archive. https://eprint.iacr.org/2017/666.
7. ↑ Chirgwin, Richard (22 August 2018). "Elders of internet hash out standards to grant encrypted message security for world+dog". https://www.theregister.co.uk/2018/08/22/ietf_draft_proposes_encrypted_message_security_for_all/. Retrieved 30 November 2018.
8. ↑ Sullivan, Nick; Turner, Sean (2023-03-29). "Messaging Layer Security: Secure and Usable End-to-End Encryption". https://www.ietf.org/blog/mls-secure-and-usable-end-to-end-encryption/.
9. ↑ "New MLS protocol provides groups better and more efficient security at Internet scale". 2023-07-19. https://www.ietf.org/blog/mls-protocol-published/.
10. ↑ Beurdouche, Benjamin; Vasquez, Sarah (2023-07-20). "Messaging Layer Security is now an internet standard". https://blog.mozilla.org/en/mozilla/messaging-layer-security-is-now-an-internet-standard/.
11. ↑ "An important step towards secure and interoperable messaging" (in en). https://security.googleblog.com/2023/07/an-important-step-towards-secure-and.html.
12. ↑ Mayo, Benjamin (2025-03-14). "End-to-end encrypted RCS messaging on iPhone coming in future software update" (in en-US). https://9to5mac.com/2025/03/14/end-to-end-encrypted-rcs-messaging-on-iphone/.
13. ↑ Van Pelt, Tom (2025-03-14). "RCS Encryption: A Leap Towards Secure and Interoperable Messaging" (in en-GB). https://www.gsma.com/newsroom/article/rcs-encryption-a-leap-towards-secure-and-interoperable-messaging/.
14. ↑ "End-to-end encrypted RCS messaging begins rolling out today in beta" (in en-US). https://www.apple.com/newsroom/2026/05/end-to-end-encrypted-rcs-messaging-begins-rolling-out-today-in-beta/.
15. ↑ "End-to-end encrypted RCS messaging begins rolling out today for Android and iPhone users" (in en-us). 2026-05-11. https://blog.google/products-and-platforms/platforms/android/android-ios-end-to-end-encrypted-rcs-messaging/.
16. ↑ "Are We MLS Yet?" (in en-US). https://arewemlsyet.com.
17. ↑ Toulas, Bill. "Discord rolls out end-to-end encryption on voice, video calls" (in en-us). https://www.bleepingcomputer.com/news/security/discord-rolls-out-end-to-end-encryption-on-voice-video-calls/.
18. ↑ "Cryspen | Post-Quantum Group Messaging". https://cryspen.com/post/pq-mls/.
19. ↑ Hashimoto, Keitaro; Katsumata, Shuichi; Prest, Thomas (2022-11-07). "How to Hide MetaData in MLS-Like Secure Group Messaging: Simple, Modular, and Post-Quantum". https://eprint.iacr.org/2022/1533.pdf.
20. ↑ "Post-quantum messaging: examining Apple's new PQ3 protocol" (in en-GB). 2024-02-22. https://pqshield.com/post-quantum-messaging-examining-apples-new-pq3-protocol/.
21. ↑ Mahy, Rohan; Barnes, Richard (2025-11-04). ﻿ML-KEM and Hybrid Cipher Suites for Messaging Layer Security﻿ (Report). Internet Engineering Task Force. https://datatracker.ietf.org/doc/draft-ietf-mls-pq-ciphersuites/.

## External links

* RFC 9420 – The Messaging Layer Security (MLS) Protocol

* v
* t
* e

Instant messaging

Protocols
(comparison)|

| Open|

* IMPP
* IRC
* Matrix
* MTProto
* RetroShare
* Signal Protocol
* SIP
* MSRP
* SIMPLE
* Tox
* XMPP
* Jingle
* WFP
* Zephyr
* DDP

|

Closed|

* MSNP
* OSCAR
* TOC
* Skype

Services|

* Band
* BBM
* Discord
* Facebook Messenger
* FireChat
* GroupMe
* Hike Messenger
* HipChat
* ICQ
* iGap
* iMessage
* IRC Networks
* Jongla
* KakaoTalk
* Kik
* Libon
* Line
* Marco Polo
* Palringo
* Signal
* Skype
* Slack
* Snapchat
* SNOW
* Tango
* Telegram
* QQ
* Textfree/Pinger
* The Palace
* Threema
* Tox
* Trillian
* Upptalk
* Viber
* Virtual Places Chat
* WeChat
* WhatsApp
* Wickr
* Windows Messenger service
* Yahoo Together
* Zulip

Clients
(comparison)|

| Single protocol|

* Allo
* Baidu Hi
* BBM
* CSipSimple
* Facebook Messenger
* FaceTime
* Fetion
* Gadu-Gadu
* GroupMe
* IBM Sametime
* ICQ
* IMVU
* Jami
* Jongla
* Linphone
* Palringo
* RetroShare
* Ricochet
* Riot.im
* Signal
* Skype
* Telegram
* Tencent QQ
* Tox
* WeChat
* WhatsApp
* Wickr
* Wire

|

Multi-protocol|

* Adium
* Ayttm
* BitlBee
* Centericq
* eBuddy
* Empathy
* Fire
* Instantbird
* Jitsi
* Kopete
* Messages/iChat
* Miranda IM
* Nimbuzz
* Pidgin
* QIP 2010
* Skype for Business
* Trillian
* Telepathy
* Upptalk

XMPP (Jabber)|

* Bombus
* ChatSecure
* Conversations
* Gajim
* Psi
* Tkabber
* Spark

MSNP|

* aMSN
* Skype

Defunct|

* List of defunct instant messaging platforms

See also|

* Backchannel
* Chat log
* Chatbot
* Contact list
* Emoticon
* File sharing
* Instant message service center
* LAN messenger
* Messaging apps
* Presence information
* Shoutbox
* SMS language
* Status message
* Videotelephony
* Voice over IP
* Webcam
* U-Report
* Web chat
* Circuit
* FirstClass
* Flock
* Fuze Box
* Glip
* Hall.com
* Yammer

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