[drk-ram]

What this changes

Closes #646.

Hardens appraise_collateral and tcb_component in prototype/snp_collateral.py:

• Verifies vcek.issuer == ask.subject and _verify_signed_by(vcek, ask) in appraise_collateral (CollateralDenied("product_chain")).
• Requires canonical base64 encoding on packet["hcl_b64"] and report_version >= 2 in appraise_collateral (CollateralDenied("platform_evidence_format")).
• Bounds now to 1 <= now <= 9007199254740991 - max_age under CollateralDenied("clock_or_age") and rejects a mismatched appraisal["profile"] under CollateralDenied("component_inputs") in tcb_component.

Validation commands and results:

• PYTHONPATH=src python -m pytest tests/test_snp_collateral.py -q -> passed
• python -m ruff check prototype/snp_collateral.py tests/test_snp_collateral.py -> passed (All checks passed!)
• python tools/check_dashes.py -> passed (no dashes outside examples/, spec/trace-v0.1.md)
• PYTHONPATH=src python tools/review_bar.py --base origin/main --head HEAD -> passed (7 changed test cases fail on behaviour at origin/main)

Type of change

• Editorial (typo, link fix, clarification: no normative effect)
• Non-breaking spec change (new optional field, new platform profile, informative addition)
• Breaking spec change (requires 14-day comment period and Project Lead sign-off)
• Schema change
• Example addition

Spec section

prototype/snp_collateral.py (experimental SEV-SNP platform collateral appraisal prototype; no normative change to spec/trace-v0.2.md)

Tests for a fix

• vcek.issuer == ask.subject, _verify_signed_by(vcek, ask), canonical hcl_b64 round-trip, and version >= 2 in appraise_collateral: tests/test_snp_collateral.py::test_appraise_collateral_verifies_vcek_issuer_and_signature_and_report_bounds
• 1 <= now <= 9007199254740991 - max_age and appraisal["profile"] == PROFILE in tcb_component: tests/test_snp_collateral.py::test_tcb_component_rejects_zero_or_overflow_now_and_wrong_profile

Changelog entry

• Fixed (prototype(snp_collateral): verify VCEK signature against ASK and enforce canonical HCL base64, report version, and component bounds #646). prototype.snp_collateral.appraise_collateral now verifies vcek.issuer == ask.subject and the ASK signature over the VCEK certificate, requires canonical base64 on hcl_b64 and report_version >= 2, and tcb_component enforces 1 <= now <= 9007199254740991 - max_age under clock_or_age and rejects mismatched appraisal["profile"].

Checklist

• DCO sign-off on all commits (git commit -s)
• Breaking changes marked with <!-- CHANGED: #NNN: description --> in spec text
• Backward compatibility statement included (for breaking changes)

[github-actions]

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[rajnisht7]

Batch response for this cluster is here: #653 (comment)