tpm.dev.tutorials/Attestation/TPM2_Quote.md

TPM2_Quote()

TPM2_Quote() computes a hash of the PCRs selected by the caller, and signs that hash, some additional metadata, and any extra data provided by the caller, with a signing key named by the caller. The caller must have access to that key, naturally.

The PCRs' values are NOT included in the quote produced by TPM2_Quote(). Instead, an attestation service can review an unsigned eventlog to ensure it leads to the same values as unsigned PCR values also provided by the attestation client, and then the attestation service can verify that the hash of the PCR values is indeed signed by the quote supplied by the client.

Inputs

• TPMI_DH_OBJECT sigHandle (handle for an AK)
• TPM2B_DATA qualifyingData (extra data)
• TPMT_SIG_SCHEME inScheme ("signing scheme to use if the schemefor signHandleis TPM_ALG_NULL")
• TPML_PCR_SELECTION PCRselect (set of PCRs to quote)

Outputs (success case)

• TPM2B_ATTEST quoted
• TPMT_SIGNATURE signature

Where TPM2B_ATTEST is basically a TPMS_ATTEST, which contains the following fields:

• TPM_GENERATED magic
• TPMI_ST_ATTEST type
• TPM2B_NAME signer (name of AK)
• TPM2B_DATA extraData ("external information supplied by caller")
• TPMS_CLOCK_INFO clockInfo ("Clock, resetCount, restartCount, and Safe")
• UINT64 firmwareVersion
• TPMU_ATTEST attested, a discriminated union with the TPMS_QUOTE_INFO arm (indicated by the TPM_ST_ATTEST_QUOTE discriminant value), which contains:
  • TPML_PCR_SELECTION pcrSelect (the set of PCRs digested by pcrDigest)
  • TPM2B_DIGEST pcrDigest (the digest of the PCRs indicated by pcrSelect)

References

• TCG TPM Library part 3: Commands, section 18.4