Assuming for a moment that we can trust our smart phones at the platform level not to lie to us, the problem of targeted backdoored builds could be mitigated so

Assuming for a moment that we can trust our smart phones at the platform level not to lie to us, the problem of targeted backdoored builds could be mitigated somewhat if the platform implemented Binary Transparency in a clever way: https://wiki.mozilla.org/Security/Binary_Transparency https://wiki.mozilla.org/Security/Binary_Transparency When you install an app (whether through an app store, or side-loading) the app should state the location online of an append-only log that lists all the releases (with timestamps) for that app. The phone OS could periodically check to see if an upgrade is available, and security researchers could check that the log doesn't contain references to versions which aren't available to the public. Ideally there should perhaps also be a way for users to anonymously report which version of any app they are using, so that people with particular security concerns could configure their OS to only update an app after, for example, 50% of users have already installed the update.