Vouchers

Overview

Security measures that prevent fake vouchers and ensure system integrity.

Voucher Creation Security

On-Chain Protection

• Authorized Creation: Only the VerifierRegistry contract can create vouchers (onlyRegistry modifier)

• Deterministic IDs: Voucher IDs generated using cryptographic hash of (qHash, targetChainId, verifierId, block.timestamp, counter)

• Collision Detection: Smart contract prevents voucher ID collisions with explicit validation

• Immutable Records: Once created, voucher data is immutably stored on-chain

Cryptographic Integrity

// Voucher ID generation (deterministic and collision-resistant)
bytes32 voucherId = keccak256(abi.encodePacked(
    qHash,           // Original proof hash
    targetChainId,   // Destination chain
    verifierId,      // Verification type
    block.timestamp, // Creation time
    totalVouchersCreated + i // Unique counter
));

Voucher Processing Security

Off-Chain Validation

• Event Deduplication: Relayer service tracks processed events to prevent double-processing

• State Management: Redis-based tracking ensures vouchers are only processed once per chain

• Hub Transaction Validation: Vouchers are only processed if linked to valid hub transactions

• Trusted Relayer Network: Only authorized relayers can fulfill vouchers on spoke chains

Spoke Chain Protection

• Relayer Authorization: Spoke contracts verify relayer is trusted before accepting voucher fulfillment

• Voucher Validation: Smart contract validates voucher structure and prevents replay attacks

• Already-Fulfilled Checks: Transaction manager validates voucher hasn't been fulfilled before sending transaction

Attack Prevention

Against Fake Vouchers

1. Creation Authority: Fake vouchers cannot be created - only VerifierRegistry can emit valid VoucherCreated events

2. Chain Validation: Relayer service only processes events from official hub contract

3. Cryptographic Binding: Voucher ID cryptographically binds to original verification proof

4. Immutable Audit Trail: All voucher creation and fulfillment is permanently recorded on-chain

Against Replay Attacks

1. One-Time Use: Each voucher can only be fulfilled once per chain

2. Deduplication: Multiple layers of duplicate detection prevent re-processing

3. State Tracking: Comprehensive state management prevents race conditions

4. Timeout Protection: Stale vouchers are automatically cleaned up

Against Unauthorized Processing

1. Trusted Relayers Only: Spoke contracts only accept fulfillment from authorized relayers

2. Multi-Layer Validation: Transaction manager validates permissions before sending transactions

3. Access Control: Smart contracts enforce strict access control for all operations

Monitoring and Auditing

Real-Time Protection

• Event Monitoring: All voucher creation and fulfillment events are logged and monitored

• Anomaly Detection: Unusual patterns in voucher processing trigger alerts

• Health Checks: Continuous monitoring of relayer service health and performance

• Balance Monitoring: Relayer wallet balances monitored to prevent service disruption

Audit Trail

• Immutable Records: All voucher operations recorded on-chain with full traceability

• Comprehensive Logging: Detailed off-chain logging for security analysis

• Metrics Tracking: Performance and security metrics tracked for analysis

• Event Correlation: Cross-chain event correlation ensures consistency

Security Guarantees

The voucher system provides these security guarantees:

1. Authenticity: All vouchers originate from verified proofs on the hub chain

2. Integrity: Voucher data cannot be tampered with once created

3. Non-Repudiation: All operations are cryptographically signed and recorded

4. Availability: Redundant relayer network ensures high availability

5. Consistency: Cross-chain state consistency maintained through careful synchronization

Risk Mitigation

Operational Risks

• Relayer Failure: Multiple trusted relayers provide redundancy

• Network Congestion: Intelligent retry logic handles network issues

• Smart Contract Bugs: Timelock upgrades and emergency pause functionality

Security Monitoring

• Failed Transactions: All failed voucher operations are logged and analyzed

• Unauthorized Attempts: Attempts to process invalid vouchers are blocked and reported

• Performance Anomalies: Unusual processing patterns trigger security alerts

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Multiple security layers ensure only legitimate vouchers are processed.