feat(mask): masking PDP — policy veto + tokenize + BEACON_COMMIT seal#25
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…reference engine)
Implements the masking-layer desensitisation primitives (the one piece not yet on
main after the gate + sealing PRs landed). Algebraic pseudonym is homomorphic under
re-keying, so domain re-tokenisation and key rotation never touch cleartext:
token = H(value)^2 ^ k(domain,epoch) mod P; retoken tweak = k2 * k1^-1 mod Q
scripts/exodus_tokenize.py
- chameleon_token / domain_tweak / retokenize (domain-scoped, cross-domain
unlinkable, key-evolving epochs).
- hmac_pseudonym + build_reid_lookup (governed re-identification dictionary).
- fpe_encrypt/decrypt (reference balanced Feistel, even-length digits).
- one_way_hash / redact / generalize / suppress.
- apply_profile() dispatches by tokenization-profile.v1 scheme.
- stdlib-only; BLAKE3 opportunistic like exodus_seal.py.
scripts/test_exodus_tokenize.py (8 tests, plain-assert idiom)
- verifies the 256-bit reference group is a safe prime; determinism;
cross-domain unlinkability; homomorphic re-tokenisation == native token;
epoch-rotation consistency; FPE round-trip + format; re-id lookup; dispatch.
Reference impl: production needs >=2048-bit MODP/EC group, constant-time bigint,
HSM-held scalars, and NIST FF1 FPE (documented in the module).
… -> masking-decision Composes the shipped pieces into one enforcement step (P1 #5), evaluated at read/export/activate/re-identify time: policy veto (forbidden identity mixtures, e.g. no_health_adtech) + exodus_tokenize (per-field Chameleon/FPE/hash/redact) + exodus_seal (BEACON_COMMIT receipt over the decision) -> a masking-decision.v1 record (the decision is itself verifiable evidence) scripts/exodus_mask.py - evaluate_masking(record, requesting_realm, audience, profiles, policy, ...): verdict allow / allow_masked / deny / review_required; applies field transforms; re-identification is reason-gated + profile-attr gated; emits masking-decision.v1 with a policy-decision ref + (signed) BEACON_COMMIT receipt. - unlinkable-identifier / side-channel mitigations recorded on every decision. scripts/test_exodus_mask.py (5 tests) - no_health_adtech veto (deny, no record returned); allow_masked tokenizes the field; re-identify requires reason + authz; signed receipt verifies via exodus_seal.verify_receipt; masking-decision.v1 shape. Depends on exodus_tokenize (PR #24). Gateway HTTP wiring (prophet-platform) is the remaining P1 #6 integration; this is the reusable PDP engine.
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Stacked on #24 (needs
exodus_tokenize). Retarget tomainonce #24 merges.The masking Policy Decision Point (P1 #5): one enforcement step composing the shipped pieces —
policy veto (no_health_adtech) + exodus_tokenize + exodus_seal → masking-decision.v1Why it beats passive masking
Every decision carries a policy-decision ref and a signed BEACON_COMMIT receipt (verified in the test via
exodus_seal.verify_receipt) — the verifiable-evidence property WKC-style dynamic masking does not produce. Tokens are domain-scoped and cross-domain-unlinkable.Behaviour
denyon forbidden identity mixtures (health + adtech), returns no record.allow_maskedapplies per-fieldtokenization-profiletransforms (Chameleon / FPE / hash / redact).re_identifyis reason-gated + profile-attr gated → governed, audited release.Tests
scripts/test_exodus_mask.py— 5 dependency-free tests, all green; tokenize (8) + gate tests still pass.Next: HTTP wiring into the Catalog Gateway read path (prophet-platform, P1 #6).
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