On Fri, 12 May 2023 at 13:04, Matthew Garrett <mjg59@xxxxxxxxxxxxx> wrote: > > On Tue, May 09, 2023 at 06:21:44PM -0700, Eric Biggers wrote: > > > SHA-1 is insecure. Why are you still using SHA-1? Don't TPMs support SHA-2 > > now? > > TXT is supported on some TPM 1.2 systems as well. TPM 2 systems are also > at the whim of the firmware in terms of whether the SHA-2 banks are > enabled. But even if the SHA-2 banks are enabled, if you suddenly stop > extending the SHA-1 banks, a malicious actor can later turn up and > extend whatever they want into them and present a SHA-1-only > attestation. Ideally whatever is handling that attestation should know > whether or not to expect an attestation with SHA-2, but the easiest way > to maintain security is to always extend all banks. > Wouldn't it make more sense to measure some terminating event into the SHA-1 banks instead?
