In a surprising move, Apple has announced today that it will adopt the RCS (Rich Communication Services) messaging standard. The feature will launch via a software update “later next year” and bring a wide range of iMessage-style features to messaging between iPhone and Android users.
Apple’s decision comes amid pressure from regulators and competitors like Google and Samsung. It also comes as RCS has continued to develop and become a more mature platform than it once was.
Accessing the keys from the server isn’t really a mystery or hidden. It’s technically possible for Apple to write software to query servers run by Google as well as any servers they created for themselves.
You don’t need implementation source code when you have open standards already.
WhatsApp actually used Signal’s development team to rollout the Signal protocol for them, but that app is still untrustworthy.
Here are the links to the documentation for these standards:
MLS - https://datatracker.ietf.org/wg/mls/documents/
Signal Protocol - https://www.signal.org/docs/
RCS - https://www.gsma.com/futurenetworks/rcs/universal-profile/ & https://www.gsma.com/futurenetworks/resources/rcs-up-2-4-uni/