[klhugo]

During a CC certification, the design-house, mask shop, and fab are certified to reduce the chances of the chip being tampered. The certification ensures that all those places have decent security practices and protocols. It helps but is quite far from completely mitigating it.

I don't have any reference of a mask being modified to give to you, but it is so easy to do it that we don't actually need evidences to be worried.

If you think about it, just by changing implantation parameters on the transistors that form a ring oscillator for generating random numbers can bias it (this does not require not even modifying the mask).

[jacquesm]

Ah yes, that makes good sense. I once built a hardware RNG and it was surprisingly hard to keep it stable over the longer term to satisfy the certification criteria. In the end I managed but it was a lot of analog voodoo and I can see how easy it would be to tamper with that in a way that would not be detectable unless you monitored the device continuously.

RNGs are a weak spot. Thank you for that example.