Not 100% sure about the iOS side of things (my guess is because App Store apps are signed by Apple and you can get a new dev cert issued to you from Apple, Appl

Not 100% sure about the iOS side of things (my guess is because App Store apps are signed by Apple and you can get a new dev cert issued to you from Apple, Apple could sign what ever app the 3 letter agency supplied them. But but someone will notice that there was a new update and it wouldn’t take long before news of which would get back to the devs, same would also apply to Android), On Android you used to have to sign your apps yourself before uploading them to the play store. The store wouldn’t accept an app signed with a different key. Even if you bypassed that (by sideloading the app for example) the OS would still refuse to update the app. It was fairly common to see on Android dev forums people posting “I’ve lost my signing key, what do I do?” To he told they gotta upload under a different package name and hope their existing users would migrate over to the “new app” Now these days Google offer to hold your signing keys for you (cause if you lose your keys you lose the ability to update the app) and if you want to use Googles App Bundle ability you have to opt in (because Google repackage your app for different device types automatically) but you are still free to hold the keys yourself and sign your builds without Google taking a peak at them. Opting into App Bundles for an existing app requires you to upload your existing signing key, so Google can sign on your behalf and devices with your existing app will accept the updates Google’s bundle process produce. Now of cause Google could push some updates to Android as a whole and make a back door to bypass app sig checking, but that would be opening holes on a lot of devices, most of which won’t actually be your target. And if we are going to go down the road of back roofing OS’s to allow apps from unknown keys, might as well just back door the OS and skip the process of creating a fake update for that one app. Now if the app is using Google’s App Bundle feature, it would be possible. But if you were creating a “secure messaging app” why would you hand the keys to the kingdom to anyone else? Just write some extra build scripts, compile the different builds your self and keep those security brownie points.