refactor(attestation): align nonce definition to implemented thumbprint+salt#358
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…bprint+salt
The codebase carried two nonce definitions. The implemented and verifier-enforced
one (startup.py + cmcp_verify._verify_key_binding + test_verify.py) is:
nonce = JWK_thumbprint(tee_public_key)(32) || random_salt(32)
with the session bound separately via the signed gateway.session_id. A second,
unused definition -- SHA-256(tee_public_key || session_id) -- lived in make_nonce,
the spec, provider docstrings, and the claim4 experiment/tests. This aligns those
to the implemented design (the better one: RFC 7638 standard key binding, per-startup
freshness via salt, and a lifecycle that fits a startup-time hardware report).
- make_nonce now returns thumbprint||salt; adds jwk_thumbprint() helper
- docs/spec/attestation.md §3.3 rewritten (+ §3.3.1 session binding); provider
report_data references updated
- claim4 experiment + tests + README rewritten around key binding / freshness /
session-binding-via-signature
- test_tee make_nonce tests updated
Verified: ruff + mypy clean, 79 affected tests pass, claim4 experiment exits 0.
NOTE: the TPM *verifier* (cmcp_verify/tpm.py qualifying_data) still checks the old
SHA-256(pubkey||session_id) formula, disagreeing with the TPM provider (which uses
the startup nonce). That is a separate, pre-existing verifier bug flagged for a
hardware-tested follow-up; not changed here.
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refactor(attestation): align nonce definition to the implemented thumbprint+salt
The codebase carried two nonce definitions. The implemented and verifier-enforced
one (startup.py + cmcp_verify._verify_key_binding + test_verify.py) is:
with the session bound separately via the signed gateway.session_id. A second,
unused definition -- SHA-256(tee_public_key || session_id) -- lived in make_nonce,
the spec, provider docstrings, and the claim4 experiment/tests. This aligns those
to the implemented design (the better one: RFC 7638 standard key binding, per-startup
freshness via salt, and a lifecycle that fits a startup-time hardware report).
report_data references updated
session-binding-via-signature
Verified: ruff + mypy clean, 79 affected tests pass, claim4 experiment exits 0.
NOTE: the TPM verifier (cmcp_verify/tpm.py qualifying_data) still checks the old
SHA-256(pubkey||session_id) formula, disagreeing with the TPM provider (which uses
the startup nonce). That is a separate, pre-existing verifier bug flagged for a
hardware-tested follow-up; not changed here.