Re: [PATCH 1/2] tpm: Compare HMAC values in constant time

On Thu, 2025-07-31 at 14:52 -0700, Eric Biggers wrote:

To prevent timing attacks, HMAC value comparison needs to be constant time.  Replace the memcmp() with the correct function, crypto_memneq().

Um, OK, I'm all for more security but how could there possibly be a timing attack in the hmac final comparison code? All it's doing is seeing if the HMAC the TPM returns matches the calculated one. Beyond this calculation, there's nothing secret about the HMAC key.

Regards,

James