<i>&quot;can we implement all security functionality in hardware&#x2F;burn it into the silicon? Or accomplish the same ends by some other means?&quot;</i><p>Yes. The software could be burnt into PROM (which is unchangeable) or one could even create a custom ROM chip, and if necessary contain hardware or code that checksums the ROM.<p>However, a company doing that must be willing to run the risk that there is a bug in that unchangeable software&#x2F;hardware and then either tell their customers that they are screwed, or that they can get a free replacement phone. It also may lengthen development cycles, as you cannot, at last minute, order your factory to open a million boxes and update that part of the firmware anymore.<p>Alternatively, a fully open phone would allow customers to inspect updates and reject them or perhaps even to partially reject them (partial rejection would prevent the case where users want a feature, but only can get it by accepting weaker security). That requires a 100% open phone (hard- and software) and enough knowledgeable people willing to invest time in looking at the code.