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Time to start building discrete transistor CPUs? This discrete 6502 project was posted here recently: https://news.ycombinator.com/item?id=11703596 https://new

by mrob 10y ago

Time to start building discrete transistor CPUs? This discrete 6502 project was posted here recently: https://news.ycombinator.com/item?id=11703596 https://news.ycombinator.com/item?id=11703596 It's far too slow for most uses, but that's mostly because NMOS logic doesn't handle the high capacitance well. NMOS logic uses MOSFETs as constantly enabled pull-up resistors, so they can't be very strong pull-ups or power consumption would be too high. I expect a CMOS design would be able to run much faster, especially with high voltage and the smallest transistors available. Individual transistors can be sampled and destructively tested, and the order they are placed can be randomized to make it harder to subvert the circuit by replacing them with microcontrollers. That leaves RAM, which is far too bulky to build from discrete transistors. But you could encrypt the ram in hardware, and mirror it across multiple chips each encrypted with different keys, and check they all read back the same once decrypted. The same could be done with mass storage devices. EDIT -- on second thoughts this will not defend against replay attacks within the storage device. I'm not sure if reliable detection of a malicious storage device is even possible without having some known good storage.

nickpsecurity 10y ago
Hardware guru that taught me warned of another risk: you can't uninvent an advance tech once it's invented. The point being such techniques assume you can inspect what's going on because you're using components you know do only X. Yet, as chips get nanoscale, you can actually embed entire CPU's and RF systems in between larger components on others that are invisible to visual inspection and might not show up in black box testing. You can try to act like those nodes and their risks don't exist but subversives can still use them against you. The simple method here might be swapping more discrete chips or components out for others that are those components plus entire SOC's. Then, once they know your configuration, they hit you. Or they tell each to leak on a different frequency or whatever all at once with them figuring it out later. All kinds of crazy stuff is possible. So, just make sure you buy older stuff under different names with cash at unusual locations. Have proxies do it for you with legit excuses. Then, use multiple systems with voter logic. Tends to work out better than alternatives. Usability issues for sure, though. :)

by mrob 10y ago

nickpsecurity 10y ago

Hardware guru that taught me warned of another risk: you can't uninvent an advance tech once it's invented. The point being such techniques assume you can inspect what's going on because you're using components you know do only X. Yet, as chips get nanoscale, you can actually embed entire CPU's and RF systems in between larger components on others that are invisible to visual inspection and might not show up in black box testing. You can try to act like those nodes and their risks don't exist but subversives can still use them against you. The simple method here might be swapping more discrete chips or components out for others that are those components plus entire SOC's. Then, once they know your configuration, they hit you. Or they tell each to leak on a different frequency or whatever all at once with them figuring it out later. All kinds of crazy stuff is possible. So, just make sure you buy older stuff under different names with cash at unusual locations. Have proxies do it for you with legit excuses. Then, use multiple systems with voter logic. Tends to work out better than alternatives. Usability issues for sure, though. :)