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Stealthy Dopant-Level Hardware Trojans (2013) [pdf] (iacr.org)
38 points by weinzierl 27 days ago | hide | past | favorite | 3 comments

I'm a little surprised the authors didn't mention that this technique was used to obfuscate the Z80 with several "trap transistors": https://www.cl.cam.ac.uk/~sps32/Z80proj/Z80_traps.pdf

As the above images, and the presence of many Soviet clones shows, the obfuscation was not entirely impossible to detect.

So if I understand this correctly...

They under-doped certain areas to create depletion mode transistors that any reverse engineer examining the silicon would expect are regular enhancement mode ones. They strategically placed a handful of these "disguised" transistors, which once incorrectly copied would switch in the opposite manner and wreak havoc on circuit operation.

According to one of the designers[1]:

I heard from NEC later the copy maker delayed the announcement of Z80 compatible product for about six months.

[1] https://retrocomputing.stackexchange.com/questions/11143/in-...

Well this is certainly eye opening, and a new level of insidious technical wizardry to me.

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