We noticed that the key from an old Zen 1 CPU was the example key of the NIST SP 800-38B publication (Appendix D.1 2b7e1516 28aed2a6 abf71588 09cf4f3c) and was reused until at least Zen 4 CPUs. Using this key we could break the two usages of AES-CMAC: the RSA public key and the microcode patch contents.

“Oh, the password is actually ‘password’” levels of security. Amazing stuff.

I guess they didn’t realise that compromising the key for the MAC would break the entire cryptosystem.

This is actually kind of cool. It’s funny that the hash algorithm is the weakness in this entire thing.