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The intro document mentions

> Here's the thing - the big vendors encrypt and sign their updates so that you cannot run your own microcode. A big discovery recently means that the authentication scheme is a lot weaker than intended, and you can now effectively "jailbreak" your CPU!

But there's no further details. I'd love to know about the specifics too!



They accidentally used the example key from AES-CMAC RFC, the full details are in the accompanying blog post: https://bughunters.google.com/blog/5424842357473280/zen-and-...


Yikes! One would have expected a little more code review or a design review from a hardware manufacturer, especially of security system. A system that people have been worried about since the Pentium FDIV bug.

I guess this one just slipped through the cracks?


Taking "never roll your own" too far.


I feel like using the example key isn’t really the big failure here.

They didn’t need a keyed hash at all, they needed a collision resistant hash.

SHA256 would have eliminated this vuln and it has a hardcoded “key” built into it.

Using a secret key for CMAC would not have been more secure, it would have just meant sophisticated hardware extraction of the key was required before this attack could be mounted.


I suppose the reuse wasn't accidental, but they mistakenly thought the key doesn't matter for CMAC.




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