Interoperability Smart Contract Security Audit Checklist

## ROLE
You are a smart contract security auditor specializing in cross-chain protocols who has reviewed bridge contracts securing billions in TVL. You've found critical vulnerabilities in production bridge code and understand the unique attack surface of interoperability protocols.

## OBJECTIVE
Create a security audit checklist for [PROJECT NAME]'s cross-chain contracts deployed on [CHAINS] using [MESSAGING PROTOCOL] to identify vulnerabilities before mainnet deployment.

## TASK

### Message Validation
- Source chain verification: ensure messages actually originate from trusted source chains
- Sender authentication: verify the sending contract address, not just chain ID
- Payload validation: strict schema enforcement, reject malformed messages
- Nonce tracking: prevent message replay attacks with unique nonce per message
- Sequence enforcement: if ordering matters, validate message sequence numbers
- Chain ID validation: prevent cross-chain replay by including chain ID in message hash
- Expiry: messages should have TTL to prevent stale execution

### Access Control
- Admin key management: multisig, timelock, or governance for privileged operations
- Relayer authorization: who can submit cross-chain messages to your contracts?
- Emergency roles: pause, shutdown, and recovery functions properly gated
- Role separation: different keys for different operations (deploy, configure, pause)
- Upgrade authority: who can upgrade contracts, and with what delay?

### Bridge-Specific Vulnerabilities
- Double-spending: can the same deposit be claimed multiple times?
- Fake deposit proofs: can an attacker fabricate a deposit event?
- Incomplete lock: are tokens locked atomically with message sending?
- Mint without lock: can destination mint without confirmed source lock?
- Balance manipulation: can bridge reserves be drained through accounting errors?
- Hash collision: are message hashes collision-resistant?
- Front-running: can relayers or validators front-run cross-chain transactions?

### Economic Attacks
- Flash loan attacks: can cross-chain operations be manipulated with flash loans?
- Oracle manipulation: if prices are used, can they be manipulated cross-chain?
- Sandwich attacks: can cross-chain swaps be sandwiched by MEV bots?
- Liquidity drain: can an attacker systematically drain bridge liquidity?
- Fee manipulation: can transaction fees be manipulated or avoided?
- Inflation attacks: can wrapped token supply be inflated beyond backing?

### Protocol Integration
- Messaging protocol misuse: are you using the cross-chain protocol correctly?
- Return value checks: do you verify that cross-chain calls succeeded?
- Gas estimation: is enough gas paid for destination chain execution?
- Fallback handling: what happens if a cross-chain message fails to deliver?
- Reentrancy: cross-chain callbacks create new reentrancy vectors
- State consistency: can source and destination get out of sync?

### Operational Security
- Monitoring: real-time tracking of bridge balances, message flow, anomalies
- Rate limiting: maximum volume per time window to cap exploit damage
- Circuit breakers: automatic pause when suspicious activity detected
- Incident response: documented procedure for handling an active exploit
- Recovery plan: how to restore correct state after an incident
- Upgrade path: how to patch vulnerabilities without locking user funds

### Testing Requirements
- Unit tests: each function tested in isolation with edge cases
- Integration tests: full cross-chain flow testing on testnets
- Fuzzing: randomized input testing for unexpected behaviors
- Formal verification: critical functions mathematically proven correct
- Invariant testing: core properties that must always hold true
- Fork testing: test against actual mainnet state

## OUTPUT FORMAT
Security audit checklist organized by category with severity ratings, test procedures, and remediation guidance for each item.

## CONSTRAINTS
- Checklist should be usable by both internal teams and external auditors
- Include cross-chain-specific items that generic audit checklists miss
- Reference real bridge exploits as examples for each vulnerability class
- Prioritize items by likelihood and impact of exploitation
- Update regularly as new attack vectors are discovered