Your demand is impossible. Any software update mechanism relies upon trusting the software vendor.^ The only thing you can ever hope for is that the update mech

Your demand is impossible. Any software update mechanism relies upon trusting the software vendor.^ The only thing you can ever hope for is that the update mechanism is capable of trusting that the update has not been tampered with in transit. ^ with the debatable exception of software distributed in source code form in a language you're able to audit and compile yourself, though you'd still be vulnerable to cleverly concealed exploits