Messaging layer security: Encrypting a group chat

How do you keep the messages in a group chat secure? Messaging layer security (MLS).
The Double Ratchet algorithm provides end-to-end encryption for text messages between two people. But securing a group chat is much harder. MLS is the first standardized multi-party “key exchange” - a protocol for communication among groups of people or devices.
Resources:
Video on the Double Ratchet algorithm: • Double ratchet algorit...
MLS Working Group: messaginglayer...
Created by Kelsey Houston-Edwards
Graphics by Ray Lux
Sponsored by Wire wire.com
Thanks to Britta Hale for the helpful conversation about MLS

[@guzh]

It is unclear how F gets its private key at 6'16''. It is also unclear why the rachet can go up the tree as well as down the tree.

[@sojn4]

It’s a bit confusing in the graphics but F must derive its own Public Private key pairs itself first, give Alice the public key, then Alice will wrap the group secrets (tree private keys) with Franks public key so that F can join the group chat. F gets its welcome message directly from Alice. Basically you can use any method to give F the welcome message.

[@sojn4]

Also think of the ratchet as the “propagation path” for a new key. The ratchet doesn’t HAVE to go unidirectional on the tree. The ratchet is in the direction of any new key that’s being propagated.

[@eapiii]

Great set of videos

[@Der_Stille_Zuschauer]

00:00 - Introduction and the Challenge 00:54 - some Ideas how to solve it 00:54 - Parallelized Conversation 01:40 - Key Systems 02:17 - Messaging Layer Security (MLS) (Tree System) 03:37 - Key System 05:00 - Key Schedule 06:50 - Root Key change 09:53 - Remove Group Member 11:13 - Conclusion

[@ericdanielski4802]

This comment should be pinned at the top.

[@fusionsid]

Thank you for this and the other video, Im currently making a chat app and couldnt find any good videos explaining group encryption

[@hashtag9990]

hey gentleman, would you like to share your wisdom? we want to implement encryption in our app too, and we are not knowledgeable enough, ofcourse you don't have to share your wisdom for nothing.

[@oncedidactic]

So easy to understand the concepts and see deeper into the space of problems and solutions. Awesome!! Thanks!

[@charleskhenry]

Amazing.

[@markcuello5]

HELP

[@tonpa]

Perfection!

[@leesweets4110]

Epic? Quit saying epic. Its clearly the other pronunciation. Because your way of doing it is ambiguous with another word.

[@PrecariousPosition]

I've never heard it aloud that way. How bizarre. I wouldn't have thought it was a controversial word

[@StevenAkinyemi]

Ikr. If pronouncing it as epic is ambigous, why not save us the confusion?