5 ms·
> Some of that information can be regained by making some assumptions about what you’re looking at, explains Aeppli. For example, we know that real interconnect
by kardos 7y ago
> Some of that information can be regained by making some assumptions about what you’re looking at, explains Aeppli. For example, we know that real interconnects can’t have certain shapes.
This sounds like the beginnings of the silicon obfuscation strategy: hiding things in silicon that lie below these assumptions
- comboy 7y agoI would guess that at the lowest level too much is dictated by physics. It may be possible to obfuscate some higher abstraction layers though.
- kaibee 7y agoI wouldn't be too sure of that. > Five individual logic cells were functionally disconnected from the rest— with no pathways that would allow them to influence the output— yet when the researcher disabled any one of them the chip lost its ability to discriminate the tones. Furthermore, the final program did not work reliably when it was loaded onto other FPGAs of the same type. https://www.damninteresting.com/on-the-origin-of-circuits/ https://www.damninteresting.com/on-the-origin-of-circuits/
- sephamorr 7y agoNote the last sentence of your quote. Device-to-device variability and production yield are opposites. I can't imagine how techniques that exploit variability between devices (with no mention of temperature, lifetime drift, etc) could be reliable.
- labawi 7y agoMaybe not the best example, but this was on FPGA. When making custom chips, you can make all sorts of tuning, including consistent hardly noticeable drifts from spec. The article says they only image the metal layers, so I guess you can do anything as long as you don't visibly change the metal layers.
- taurath 7y agoThis has already existed for a while!
- heyitsguay 7y agoMaybe! I've got some experience with tomographic algorithms, and what they're referring to is correcting for the "missing wedge" in the Radon and/or Fourier transforms - the measurements that tomography produces - of the chip (https://images.app.goo.gl/HWPX2LKBsDd7eeBe6 https://images.app.goo.gl/HWPX2LKBsDd7eeBe6). There has been lots of interest in statistical or data-driven algorithms to reconstruct missing measurement areas from the existing ones. It sounds like a key technology here was better algorithms to accommodate a larger missing wedge, so they didn't have to tilt the chip to extreme angles when getting projections. It's possible you could fool the algorithm in some way, but you'd have pretty weird and severe constraints on the shapes of your hidden parts to hide their presence from low-angle projections. They're probably not actually hand-crafting geometric assumptions about chip structures or anything like that.
- kardos 7y agoYep that's exactly the idea. Basically the silicon version of the underhanded C contest [1] [1] http://www.underhanded-c.org/ http://www.underhanded-c.org/
- heyitsguay 7y agoCool! Know of any websites or writeups about the silicon version?
- kardos 7y agoUnfortunately no but it would be highly interesting to read!
- abbeyj 7y agoSome anti-reverse-engineering work was put into the Z80 chip 45 years ago. https://retrocomputing.stackexchange.com/questions/11143/in-the-original-z80-layout-where-are-the-traps-located-and-what-are-their-ef https://retrocomputing.stackexchange.com/questions/11143/in-...
- 7y ago