MLDSA PCR flow

[calebofearth]

@mojtaba-bisheh to add details

[mojtaba-bisheh]

In Caliptra 1.x, we have a hardware flow that computes hashed_pcr = SHA384(pcr0 || pcr1 || ...), which is then used as a message to be signed by ECC. For pcr signing, a dedicated KV slot (slot 7) is provided for the 384-bit key.

The proposal for dual signature in Caliptra 2.0 is as follows:

Update the hashed_pcr flow to use SHA512, resulting in hashed_pcr = SHA512(pcr0 || pcr1 || ...).
Use the same results for both ECC and MLDSA.

• The 384-bit portion of hashed_pcr will be signed by ECC.
• The entire 512-bit of hashed_pcr will be signed by MLDSA.

Assign another KV slot (SLOT 8) dedicated to MLDSA to ensure domain separation between ECC and MLDSA.