feat(confidential): add compliance clawback - #855
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Revocation folds the escrowed allowance commitment back into the owner's spendable commitment by homomorphic addition, exactly like merge (DESIGN §7.4). The escrowed amount was range-proven when the delegation was created and re-bounded on every spender transfer, and the next spend re-bounds the result, so the RevokeSpender circuit proved nothing the protocol did not already know. The auditor stays in sync because it can now derive the allowance blinding from the escrowed dvk_i (S14 / O_a9). BREAKING CHANGE: revoke_spender drops its `data` argument, the RevokeSpender event carries `(a_tilde, allowance_salt)` instead of the checkpoint fields, `on_revoke_spender` loses its payload, and CircuitType::RevokeSpender is removed.
Adds the ConfidentialClawback trait: an admin- and auditor-gated seizure of a frozen account's confidential claim, plus a forced revoke that pulls escrowed allowances back into reach of the seize. The Clawback circuit proves knowledge of the openings of C_spend and C_receive and bounds the seize by their sum (CB1-CB3). Post-verification is the merge rule plus a public debit with no fresh randomness, so the seized account stays spendable. Settlement is `None` (pool left over-collateralized) or `Some(d)` (exactly `amount` transferred), with the destination bound into the proof.
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Stack 3/3. Base:
feat/conf-token-proofless-revoke(#854), which sits onfeat/conf-token-auditor-escrow(#853).What
Adds
ConfidentialClawback: an opt-in, admin- and auditor-gated seizure of a frozen account's confidential claim, plus a forced revoke that pulls escrowed allowances into reach of the seize.circuits/clawback/(51 ACIR opcodes — the cheapest circuit afterRegister) + VKCircuitType::Clawback = 5ConfidentialClawbacktrait,clawbackandforce_revoke_spenderstorage fnsset_commitments(pub(crate)),pub(crate)promotion ofverify/append_*AccountNotFrozen3604,InvalidClawbackAmount3605,InvalidClawbackDestination3606),ClawbackeventThe mechanism
The circuit proves what the contract cannot check itself, since the balances are committed: knowledge of the Pedersen openings of
C_spend(CB1) andC_receive(CB2), and that the seize is bounded by what those openings hold,α ≤ v_s + v_r(CB3).The witness is producible by anyone holding the openings — the auditor, or the owner — and not by the admin, which holds no blinding. That asymmetry is the two-party separation: the compliance authority decides whether, the auditor decides how much and where to.
Post-verification is the merge rule plus a public debit —
C_spend ← C_spend + C_receive − α·G,C_receive ← O— with no fresh randomness. The new opening(v_s + v_r − α, r_s + r_r)is recomputable by both owner and auditor, so the seized account stays spendable. Re-randomizing under an admin-chosen blinding would brick the account permanently._dest_fis an unconstrained public input that binds the settlement destination. Dropping it turns a compromised clawback signer from a griefer into a thief.Clawback = 5reuses the valueRevokeSpendervacated in #854. Admissible only against a verifier registry deployed fresh with an all-new key set.Clawback = 6avoids the hazard at zero cost — recommend changing before merge.Known gaps
circuits/clawback/src/tests.nr(10 tests).ConfidentialClawback: ConfidentialCompliancedoes not force a gatingHooksimpl. A deployment wiringNoHooksgets a freeze that sets the flag while every operation stays ungated — the target can spend out before the seize lands. Documented as a deployment obligation in COMPLIANCE.md §5.3; not enforceable by the trait bound.Checks
nargo test144 passed ·cargo test -p stellar-tokens723 passed ·cargo +nightly fmt --checkclean ·cargo clippy --all-targetsclean ·constraints.baselineregenerated