@theruran @psf Worth reading the original paper on defective CPUs. https://sigops.org/s/conferences/hotos/2021/papers/hotos21-s01-hochschild.pdf
> A deterministic AES miscomputation, which was “self-inverting”: encrypting and decrypting on the same core yielded the identity function, but decryption else where yielded gibberish.
This reminds me of a story from one flatmate who repaired machine for a supplier who had a warehouse in North London.
Their work-flow process meant that the desktop machine would arrive in the warehouse to be stored there, before being sent ot the test-lab where my flatmate worked.
They would test the machines, then send the back to a different part of the warehouse before the machines were sent to the customer's offices.
When the machines were in the offices they would start crashing after 3 days.
So replacements were sent out, and the original machines would be sent back to the warehouse where they were stored until they could be tested again.
All of the tests came out fine, so they were sent back to the warehouse before being sent out to a different set of customers.
Rinse-And-Repeat for several iterations, before they got serious in trying to trace the problems.
Eventually someone noticed that the machines that were failing had a common element.
They were using +/-10% rated-value resistors.
When they started testing the resistors, they found that ALL of the resistor ratings were either -10% to -5% rated value, or +5% to +10% rated value.
NONE of them were in the centre bands.
That's when they worked out that the resistor manufacturer had been cherry-picking the resistors from the manufacturing process.
All of the most accurate resistors went into the +/-0.1% product line, the next batch wen into the =/-2% product line, then +/-5%, and the +/-10% product line that my flatmate came across.
He ordered batches directly from a range of resistor suppliers.
ALL of the resistor manufacturers were doing it.
My flatmate showed me the machines that he was working on, as well as showing me the results from the component tests that he performed. :D
He got a pay-raise from that, while the idiot who tried to cut the quality was made redundant.
That whole company was shuttered two years later, as no-one trusted that brand, so stopped buying their machines.
It may be folklore, but i saw it happen. :D