It’s been three months and there is no documentation about what messages use Signal, what messages use MLS, the specifics of the encoding (I’m guessing the base64 blob is just raw Signal/MLS, but who knows?), and I can’t find much information about Google’s key servers.
They’ve documented the encryption primitives they use for Signal-style messaging, but that documentation uses phrases like “The RCS file transfer XML is extended to include this encrypted payload”. Extended in what way? Where’s the schema? Are they using the same mechanisms in MLS?
They haven’t closed off their implementation like iMessage has, but they also haven’t done much to allow external integration. Building a compatible client will still involve reverse engineering the Google Messages app with packet traces/eBPF captures and interpreting the XML and their binary schemas (and hopefully not get the details wrong).
Meanwhile, Apple has promised to support the Universal Profile. We have no promises of E2EE support at the moment. Even if Apple could easily get the necessary documentation from Google, who’s to say they will? If they don’t, they can label any group text “insecure” when RCS gets involved, which should help push people back into Apple’s walled garden.
Google uses the Signal protocol for encryption and they do intend to allow for interoperability:
https://9to5google.com/2023/07/19/google-messages-mls-encrypted/
This is not something Google was ever against doing
It’s been three months and there is no documentation about what messages use Signal, what messages use MLS, the specifics of the encoding (I’m guessing the base64 blob is just raw Signal/MLS, but who knows?), and I can’t find much information about Google’s key servers.
They’ve documented the encryption primitives they use for Signal-style messaging, but that documentation uses phrases like “The RCS file transfer XML is extended to include this encrypted payload”. Extended in what way? Where’s the schema? Are they using the same mechanisms in MLS?
They haven’t closed off their implementation like iMessage has, but they also haven’t done much to allow external integration. Building a compatible client will still involve reverse engineering the Google Messages app with packet traces/eBPF captures and interpreting the XML and their binary schemas (and hopefully not get the details wrong).
Meanwhile, Apple has promised to support the Universal Profile. We have no promises of E2EE support at the moment. Even if Apple could easily get the necessary documentation from Google, who’s to say they will? If they don’t, they can label any group text “insecure” when RCS gets involved, which should help push people back into Apple’s walled garden.