See "Rich Communication Suite – End-to-End Encryption Specification Version 1.0" PDF:
> RCS will rely on Messaging Layer Security (MLS) Protocol, which is an IETF specification [RFC9420], for supporting end-to-end encryption. MLS is a formally verified standard that guarantees both forward secrecy and post-compromise security for messaging in 1-to-1 and group conversations. It is designed to scale efficiently with large group chats, and it supports post-quantum encryption.
> RCS will rely on Messaging Layer Security (MLS) Protocol, which is an IETF specification [RFC9420], for supporting end-to-end encryption. MLS is a formally verified standard that guarantees both forward secrecy and post-compromise security for messaging in 1-to-1 and group conversations. It is designed to scale efficiently with large group chats, and it supports post-quantum encryption.
* https://www.gsma.com/solutions-and-impact/technologies/netwo...
* https://datatracker.ietf.org/doc/html/rfc9420
* https://en.wikipedia.org/wiki/Messaging_Layer_Security