&gt; If Apple can update OS on their phones it&#x27;s not by some magical power that nobody else can possible posses.<p>Yeah, it&#x27;s only signed by cryptographic keys that nobody else is likely to ever possess.<p>You &quot;only&quot; need to put in a new Boot ROM with your own key (&quot;When an iOS device is turned on, its application processor immediately executes code from read-only memory known as the Boot ROM. [...] The Boot ROM code contains the Apple Root CA public key, which is used to verify that the Low-Level Bootloader (LLB) is signed by Apple before allowing it to load.&quot; <a href="https:&#x2F;&#x2F;www.apple.com&#x2F;business&#x2F;docs&#x2F;iOS_Security_Guide.pdf" rel="nofollow">https:&#x2F;&#x2F;www.apple.com&#x2F;business&#x2F;docs&#x2F;iOS_Security_Guide.pdf</a>)  AFAICT this ROM is probably deeply integrated into the CPU, so hopefully you have some <i>really</i> precise tools and&#x2F;or plan to make your own replacement CPU as well.