[person3]

I don’t know a lot about how it works, so forgive me if this is a silly idea. I wonder if attestation could be done using real Apple devices, while leaving the private key on the user’s android. So similar to the old beeper to get the signed attestation, and send the result to the phone. Still could be secure since you can keep the private key used to encrypt messages local on the users device. I guess the issue might be a cat and mouse game if detecting beepers flock of Apple hardware to try and disable them all… (given many people would be using the same Apple devices)

[dwaite]

I think iMessage is still using older attestations, but generally an attestation of this sort (App Attest, Play Protect API) represent a chain of the hardware, boot process, OS and application.

So iMessage is not going to be willing to hand out private keys or negotiate them for a third party application, and Beeper will not be trusted to register a private key itself.

Android iMessage support would be weird because there is no iMessage application - there is an application which lets you send SMS and to upgrade to MMS or iMessage when available. So, if there ever was an official Messages app for Android, I would somewhat expect it to also offer to take over being the default application for SMS/MMS.