The result’s that if you wish to send a secure RCS message between Android devices, you have to use Google’s own Messages app at each ends; it implements E2EE using the well-worn Signal protocol. Similarly, Apple adopted RCS in iMessage last yr, but with a proprietary implementation of E2EE.
In brief, it’s a confusing jumble. That is one reason why alternatives similar to WhatsApp and Signal, each of which also use the Signal protocol, have turn out to be so popular; you get E2EE out of the box without compatibility worries, and so they allow groups of as much as 1,024 members.
Having a single protocol, MLS, covering E2EE changes the story. Now RCS with MLS can offer a variety of advanced features including large groups, that are critical for businesses which need many-to-many communication. Right away, if even one user in a gaggle is using an RCS app without compatible E2EE, the safety of the entire group chat may be compromised. MLS gives every app maker one IETF standard to aim for.
