Cross-Chain Messaging

Normative rules for producing, waiting on, and consuming L1↔L2 messages.

Message Identity

CROSS-1. An L1ToL2Message MUST bind all of {sender: L1Actor, recipient: L2Actor, content: Fr, secret_hash: Fr}. Altering any field produces a distinct message and MUST NOT succeed as a replacement for the original.

CROSS-2. secret_hash MUST be computed from the secret via the Aztec-canonical derivation (see aztec_ethereum::messaging::generate_claim_secret); arbitrary hashes MUST NOT be accepted on the consumption side.

CROSS-3. generate_claim_secret() MUST use a cryptographically secure random source. Implementations that seed it deterministically across tx submissions are a vulnerability.

L1 → L2 Production

CROSS-4. send_l1_to_l2_message MUST target the Inbox address obtained from the Aztec node’s NodeInfo (L1ContractAddresses::from_json); hard-coded Inbox addresses MUST NOT be used across networks.

CROSS-5. An L1ToL2MessageSentResult MUST carry both the L1 tx hash and the derived L2 message hash; consumers MUST use the L2 message hash (not the L1 tx hash) for readiness checks.

Readiness

CROSS-6. is_l1_to_l2_message_ready MUST return false until the node’s archiver has committed the enclosing L1 block. A true response is the precondition for consumption.

CROSS-7. Readiness is advisory relative to L1 finality. Applications that require L1 finality MUST additionally wait for the L2 block consuming the message to reach Proven.

L1 → L2 Consumption

CROSS-8. An L2 consumer MUST supply both the secret and the exact content originally produced. Kernel verification MUST reject mismatches.

CROSS-9. A message MUST be consumed at most once. The network enforces this via the L1-to-L2 nullifier tree; clients MUST NOT attempt to replay a successful consumption.

L2 → L1

CROSS-10. An L2-emitted message MUST NOT be treated as consumable on L1 before the enclosing block is Proven.

CROSS-11. L1-side consumption MUST verify the inclusion proof against the Outbox root stored in the L1 rollup contract.

CROSS-12. An L2-to-L1 message MUST be consumed at most once on L1; the Outbox enforces this.

Fee Juice Bridge

CROSS-13. prepare_fee_juice_on_l1 MUST produce an L2AmountClaim whose secret_hash matches the one used in the L1 deposit; applications MUST NOT use a different secret/hash pair for the corresponding FeeJuicePaymentMethodWithClaim.

CROSS-14. The L2AmountClaim produced by a bridge helper MUST be usable exactly once; after consumption it MUST be discarded.