Saint EntrySign, Who Signed the Microcode With the Wrong Key

Patron of AMD processors, microcode, and example keys copied out of the manuals.

Life

In early 2025 researchers at Google revealed EntrySign, a flaw in the microcode signature check of AMD Zen processors. The check used AES-CMAC as if it were a hash function, and on top of that with an example key taken from NIST documentation: so anyone with administrator privileges could load arbitrary microcode and rewrite the CPU's behaviour. The full fix requires a BIOS update.

Prayer

O Saint EntrySign, who sign the microcode with the key from the manual, let our checks use secret keys and functions made for the purpose. Amen.

How to celebrate

Celebrated by installing AMD BIOS and microcode updates and never reusing the NIST example keys.

A key from the manual, a signature of cardboard.