For the context, the vast majority of carriers do RCS with Google's RCS servers (https://github.com/phhusson/rcs-scanner). I'm a bit rusty, but to my knowledge the only exceptions are Jio in India, all Chinese telcos, and some Japenese telcos.
Of course it is relevant privacy-wise (Google still gather a lot of metadata about who speaks to who and when), but that's not even the reason I'm mentioning it.
In the RCS specification, there are three lines on a killer-feature: device attestation. A server can whitelist which devices are allowed to connect to it. And of course Google uses this, allowing only Google-certified devices and Apple devices.
And then, there is actually one RCS client for Google's RCS servers. Because Google Messages doesn't use RCS, it uses a custom protocol based on protobuf. My personal guess is that this protobuf is a 1-to-1 matching with actual RCS, and it's both-way compatible. But still, that means that potentially the Google device-attestation won't work with an RCS client.
Sibling comments say that GrapheneOS plan on implementing it. I think it can reasonably work. TBH I'm expecting that giving a LLM the publicly available information about RCS on microG should give a working "send message" within a day (even when using Google apps rather than microG, it's just that the microG work explains the API). And once RCS work in GrapheneOS' message app, it should be pretty straightforward to port to microG, so yay. However I have to admit I'm not optimist about how long it will keep working. I'd say we are two years away from Google enforcing RKP device integrity for RCS, and uh, good luck passing that.
Of course, I'm hoping that, in the EU, the DMA will break this Google/Apple-only device-attestation, but I'm not aware of anyone pushing that ATM.
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For the context, the vast majority of carriers do RCS with Google's RCS servers (https://github.com/phhusson/rcs-scanner). I'm a bit rusty, but to my knowledge the only exceptions are Jio in India, all Chinese telcos, and some Japenese telcos.
Of course it is relevant privacy-wise (Google still gather a lot of metadata about who speaks to who and when), but that's not even the reason I'm mentioning it.
In the RCS specification, there are three lines on a killer-feature: device attestation. A server can whitelist which devices are allowed to connect to it. And of course Google uses this, allowing only Google-certified devices and Apple devices.
And then, there is actually one RCS client for Google's RCS servers. Because Google Messages doesn't use RCS, it uses a custom protocol based on protobuf. My personal guess is that this protobuf is a 1-to-1 matching with actual RCS, and it's both-way compatible. But still, that means that potentially the Google device-attestation won't work with an RCS client.
Sibling comments say that GrapheneOS plan on implementing it. I think it can reasonably work. TBH I'm expecting that giving a LLM the publicly available information about RCS on microG should give a working "send message" within a day (even when using Google apps rather than microG, it's just that the microG work explains the API). And once RCS work in GrapheneOS' message app, it should be pretty straightforward to port to microG, so yay. However I have to admit I'm not optimist about how long it will keep working. I'd say we are two years away from Google enforcing RKP device integrity for RCS, and uh, good luck passing that.
Of course, I'm hoping that, in the EU, the DMA will break this Google/Apple-only device-attestation, but I'm not aware of anyone pushing that ATM.