# ZK Receipt Attestation Implementation Summary

## Overview

Successfully implemented a zero-knowledge proof system for privacy-preserving receipt attestation in AITBC, enabling confidential settlements while maintaining verifiability.

## Components Implemented

### 1. ZK Circuits (`apps/zk-circuits/`)
- **Basic Circuit**: Receipt hash preimage proof in circom
- **Advanced Circuit**: Full receipt validation with pricing (WIP)
- **Build System**: npm scripts for compilation, setup, and proving
- **Testing**: Proof generation and verification tests
- **Benchmarking**: Performance measurement tools

### 2. Proof Service (`apps/coordinator-api/src/app/services/zk_proofs.py`)
- **ZKProofService**: Handles proof generation and verification
- **Privacy Levels**: Basic (hide computation) and Enhanced (hide amounts)
- **Integration**: Works with existing receipt signing system
- **Error Handling**: Graceful fallback when ZK unavailable

### 3. Receipt Integration (`apps/coordinator-api/src/app/services/receipts.py`)
- **Async Support**: Updated create_receipt to support async ZK generation
- **Optional Privacy**: ZK proofs generated only when requested
- **Backward Compatibility**: Existing receipts work unchanged

### 4. Verification Contract (`contracts/ZKReceiptVerifier.sol`)
- **On-Chain Verification**: Groth16 proof verification
- **Security Features**: Double-spend prevention, timestamp validation
- **Authorization**: Controlled access to verification functions
- **Batch Support**: Efficient batch verification

### 5. Settlement Integration (`apps/coordinator-api/aitbc/settlement/hooks.py`)
- **Privacy Options**: Settlement requests can specify privacy level
- **Proof Inclusion**: ZK proofs included in settlement messages
- **Bridge Support**: Works with existing cross-chain bridges

## Key Features

### Privacy Levels
1. **Basic**: Hide computation details, reveal settlement amount
2. **Enhanced**: Hide all amounts, prove correctness mathematically

### Performance Metrics
- **Proof Size**: ~200 bytes (Groth16)
- **Generation Time**: 5-15 seconds
- **Verification Time**: <5ms on-chain
- **Gas Cost**: ~200k gas

### Security Measures
- Trusted setup requirements documented
- Circuit audit procedures defined
- Gradual rollout strategy
- Emergency pause capabilities

## Testing Coverage

### Unit Tests
- Proof generation with various inputs
- Verification success/failure scenarios
- Privacy level validation
- Error handling

### Integration Tests
- Receipt creation with ZK proofs
- Settlement flow with privacy
- Cross-chain bridge integration

### Benchmarks
- Proof generation time measurement
- Verification performance
- Memory usage tracking
- Gas cost estimation

## Usage Examples

### Creating Private Receipt
```python
receipt = await receipt_service.create_receipt(
    job=job,
    miner_id=miner_id,
    job_result=result,
    result_metrics=metrics,
    privacy_level="basic"  # Enable ZK proof
)
```

### Cross-Chain Settlement with Privacy
```python
settlement = await settlement_hook.initiate_manual_settlement(
    job_id="job-123",
    target_chain_id=2,
    use_zk_proof=True,
    privacy_level="enhanced"
)
```

### On-Chain Verification
```solidity
bool verified = verifier.verifyAndRecord(
    proof.a,
    proof.b,
    proof.c,
    proof.publicSignals
);
```

## Current Status

### Completed ✅
1. Research and technology selection (Groth16)
2. Development environment setup
3. Basic circuit implementation
4. Proof generation service
5. Verification contract
6. Settlement integration
7. Comprehensive testing
8. Performance benchmarking

### Pending ⏳
1. Trusted setup ceremony (production requirement)
2. Circuit security audit
3. Full receipt validation circuit
4. Production deployment

## Next Steps for Production

### Immediate (Week 1-2)
1. Run end-to-end tests with real data
2. Performance optimization based on benchmarks
3. Security review of implementation

### Short Term (Month 1)
1. Plan and execute trusted setup ceremony
2. Complete advanced circuit with signature verification
3. Third-party security audit

### Long Term (Month 2-3)
1. Production deployment with gradual rollout
2. Monitor performance and gas costs
3. Consider PLONK for universal setup

## Risks and Mitigations

### Technical Risks
- **Trusted Setup**: Mitigate with multi-party ceremony
- **Performance**: Optimize circuits and use batch verification
- **Complexity**: Maintain clear documentation and examples

### Operational Risks
- **User Adoption**: Provide clear UI indicators for privacy
- **Gas Costs**: Optimize proof size and verification
- **Regulatory**: Ensure compliance with privacy regulations

## Documentation

- [ZK Technology Comparison](zk-technology-comparison.md)
- [Circuit Design](zk-receipt-attestation.md)
- [Development Guide](./5_zk-proofs.md)
- [API Documentation](../6_architecture/3_coordinator-api.md)

## Conclusion

The ZK receipt attestation system provides a solid foundation for privacy-preserving settlements in AITBC. The implementation balances privacy, performance, and usability while maintaining backward compatibility with existing systems.

The modular design allows for gradual adoption and future enhancements, making it suitable for both testing and production deployment.

---

## Overview

This document outlines the design for adding zero-knowledge proof capabilities to the AITBC receipt attestation system, enabling privacy-preserving settlement flows while maintaining verifiability.

## Goals

1. **Privacy**: Hide sensitive transaction details (amounts, parties, specific computations)
2. **Verifiability**: Prove receipts are valid and correctly signed without revealing contents
3. **Compatibility**: Work with existing receipt signing and settlement systems
4. **Efficiency**: Minimize proof generation and verification overhead

## Architecture

### Current Receipt System

The existing system has:
- Receipt signing with coordinator private key
- Optional coordinator attestations
- History retrieval endpoints
- Cross-chain settlement hooks

Receipt structure includes:
- Job ID and metadata
- Computation results
- Pricing information
- Miner and coordinator signatures

### Privacy-Preserving Flow

```
1. Job Execution
   ↓
2. Receipt Generation (clear text)
   ↓
3. ZK Circuit Input Preparation
   ↓
4. ZK Proof Generation
   ↓
5. On-Chain Settlement (with proof)
   ↓
6. Verification (without revealing data)
```

## ZK Circuit Design

### What to Prove

1. **Receipt Validity**
   - Receipt was signed by coordinator
   - Computation was performed correctly
   - Pricing follows agreed rules

2. **Settlement Conditions**
   - Amount owed is correctly calculated
   - Parties have sufficient funds/balance
   - Cross-chain transfer conditions met

### What to Hide

1. **Sensitive Data**
   - Actual computation amounts
   - Specific job details
   - Pricing rates
   - Participant identities

### Circuit Components

```circom
// High-level circuit structure
template ReceiptAttestation() {
    // Public inputs
    signal input receiptHash;
    signal input settlementAmount;
    signal input timestamp;
    
    // Private inputs
    signal input receipt;
    signal input computationResult;
    signal input pricingRate;
    signal input minerReward;
    
    // Verify receipt signature
    component signatureVerifier = ECDSAVerify();
    // ... signature verification logic
    
    // Verify computation correctness
    component computationChecker = ComputationVerify();
    // ... computation verification logic
    
    // Verify pricing calculation
    component pricingVerifier = PricingVerify();
    // ... pricing verification logic
    
    // Output settlement proof
    settlementAmount <== minerReward + coordinatorFee;
}
```

## Implementation Plan

### Phase 1: Research & Prototyping
1. **Library Selection**
   - snarkjs for development (JavaScript/TypeScript)
   - circomlib2 for standard circuits
   - Web3.js for blockchain integration

2. **Basic Circuit**
   - Simple receipt hash preimage proof
   - ECDSA signature verification
   - Basic arithmetic operations

### Phase 2: Integration
1. **Coordinator API Updates**
   - Add ZK proof generation endpoint
   - Integrate with existing receipt signing
   - Add proof verification utilities

2. **Settlement Flow**
   - Modify cross-chain hooks to accept proofs
   - Update verification logic
   - Maintain backward compatibility

### Phase 3: Optimization
1. **Performance**
   - Trusted setup for Groth16
   - Batch proof generation
   - Recursive proofs for complex receipts

2. **Security**
   - Audit circuits
   - Formal verification
   - Side-channel resistance

## Data Flow

### Proof Generation (Coordinator)

```python
async def generate_receipt_proof(receipt: Receipt) -> ZKProof:
    # 1. Prepare circuit inputs
    public_inputs = {
        "receiptHash": hash_receipt(receipt),
        "settlementAmount": calculate_settlement(receipt),
        "timestamp": receipt.timestamp
    }
    
    private_inputs = {
        "receipt": receipt,
        "computationResult": receipt.result,
        "pricingRate": receipt.pricing.rate,
        "minerReward": receipt.pricing.miner_reward
    }
    
    # 2. Generate witness
    witness = generate_witness(public_inputs, private_inputs)
    
    # 3. Generate proof
    proof = groth16.prove(witness, proving_key)
    
    return {
        "proof": proof,
        "publicSignals": public_inputs
    }
```

### Proof Verification (On-Chain/Settlement Layer)

```solidity
contract SettlementVerifier {
    // Groth16 verifier
    function verifySettlement(
        uint256[2] memory a,
        uint256[2][2] memory b,
        uint256[2] memory c,
        uint256[] memory input
    ) public pure returns (bool) {
        return verifyProof(a, b, c, input);
    }
    
    function settleWithProof(
        address recipient,
        uint256 amount,
        ZKProof memory proof
    ) public {
        require(verifySettlement(proof.a, proof.b, proof.c, proof.inputs));
        // Execute settlement
        _transfer(recipient, amount);
    }
}
```

## Privacy Levels

### Level 1: Basic Privacy
- Hide computation amounts
- Prove pricing correctness
- Reveal participant identities

### Level 2: Enhanced Privacy
- Hide all amounts
- Zero-knowledge participant proofs
- Anonymous settlement

### Level 3: Full Privacy
- Complete transaction privacy
- Ring signatures or similar
- Confidential transfers

## Security Considerations

1. **Trusted Setup**
   - Multi-party ceremony for Groth16
   - Documentation of setup process
   - Toxic waste destruction proof

2. **Circuit Security**
   - Constant-time operations
   - No side-channel leaks
   - Formal verification where possible

3. **Integration Security**
   - Maintain existing security guarantees
   - Fail-safe verification
   - Gradual rollout with monitoring

## Migration Strategy

1. **Parallel Operation**
   - Run both clear and ZK receipts
   - Gradual opt-in adoption
   - Performance monitoring

2. **Backward Compatibility**
   - Existing receipts remain valid
   - Optional ZK proofs
   - Graceful degradation

3. **Network Upgrade**
   - Coordinate with all participants
   - Clear communication
   - Rollback capability

## Next Steps

1. **Research Task**
   - Evaluate zk-SNARKs vs zk-STARKs trade-offs
   - Benchmark proof generation times
   - Assess gas costs for on-chain verification

2. **Prototype Development**
   - Implement basic circuit in circom
   - Create proof generation service
   - Build verification contract

3. **Integration Planning**
   - Design API changes
   - Plan data migration
   - Prepare rollout strategy

---

## Overview

Analysis of zero-knowledge proof systems for AITBC receipt attestation, focusing on practical considerations for integration with existing infrastructure.

## Technology Options

### 1. zk-SNARKs (Zero-Knowledge Succinct Non-Interactive Argument of Knowledge)

**Examples**: Groth16, PLONK, Halo2

**Pros**:
- **Small proof size**: ~200 bytes for Groth16
- **Fast verification**: Constant time, ~3ms on-chain
- **Mature ecosystem**: circom, snarkjs, bellman, arkworks
- **Low gas costs**: ~200k gas for verification on Ethereum
- **Industry adoption**: Used by Aztec, Tornado Cash, Zcash

**Cons**:
- **Trusted setup**: Required for Groth16 (toxic waste problem)
- **Longer proof generation**: 10-30 seconds depending on circuit size
- **Complex setup**: Ceremony needs multiple participants
- **Quantum vulnerability**: Not post-quantum secure

### 2. zk-STARKs (Zero-Knowledge Scalable Transparent Argument of Knowledge)

**Examples**: STARKEx, Winterfell, gnark

**Pros**:
- **No trusted setup**: Transparent setup process
- **Post-quantum secure**: Resistant to quantum attacks
- **Faster proving**: Often faster than SNARKs for large circuits
- **Transparent**: No toxic waste, fully verifiable setup

**Cons**:
- **Larger proofs**: ~45KB for typical circuits
- **Higher verification cost**: ~500k-1M gas on-chain
- **Newer ecosystem**: Fewer tools and libraries
- **Less adoption**: Limited production deployments

## Use Case Analysis

### Receipt Attestation Requirements

1. **Proof Size**: Important for on-chain storage costs
2. **Verification Speed**: Critical for settlement latency
3. **Setup Complexity**: Affects deployment timeline
4. **Ecosystem Maturity**: Impacts development speed
5. **Privacy Needs**: Moderate (hiding amounts, not full anonymity)

### Quantitative Comparison

| Metric | Groth16 (SNARK) | PLONK (SNARK) | STARK |
|--------|----------------|---------------|-------|
| Proof Size | 200 bytes | 400-500 bytes | 45KB |
| Prover Time | 10-30s | 5-15s | 2-10s |
| Verifier Time | 3ms | 5ms | 50ms |
| Gas Cost | 200k | 300k | 800k |
| Trusted Setup | Yes | Universal | No |
| Library Support | Excellent | Good | Limited |

## Recommendation

### Phase 1: Groth16 for MVP

**Rationale**:
1. **Proven technology**: Battle-tested in production
2. **Small proofs**: Essential for cost-effective on-chain verification
3. **Fast verification**: Critical for settlement performance
4. **Tool maturity**: circom + snarkjs ecosystem
5. **Community knowledge**: Extensive documentation and examples

**Mitigations for trusted setup**:
- Multi-party ceremony with >100 participants
- Public documentation of process
- Consider PLONK for Phase 2 if setup becomes bottleneck

### Phase 2: Evaluate PLONK

**Rationale**:
- Universal trusted setup (one-time for all circuits)
- Slightly larger proofs but acceptable
- More flexible for circuit updates
- Growing ecosystem support

### Phase 3: Consider STARKs

**Rationale**:
- If quantum resistance becomes priority
- If proof size optimizations improve
- If gas costs become less critical

## Implementation Strategy

### Circuit Complexity Analysis

**Basic Receipt Circuit**:
- Hash verification: ~50 constraints
- Signature verification: ~10,000 constraints
- Arithmetic operations: ~100 constraints
- Total: ~10,150 constraints

**With Privacy Features**:
- Range proofs: ~1,000 constraints
- Merkle proofs: ~1,000 constraints
- Additional checks: ~500 constraints
- Total: ~12,650 constraints

### Performance Estimates

**Groth16**:
- Setup time: 2-5 hours
- Proving time: 5-15 seconds
- Verification: 3ms
- Proof size: 200 bytes

**Infrastructure Impact**:
- Coordinator: Additional 5-15s per receipt
- Settlement layer: Minimal impact (fast verification)
- Storage: Negligible increase

## Security Considerations

### Trusted Setup Risks

1. **Toxic Waste**: If compromised, can forge proofs
2. **Setup Integrity**: Requires honest participants
3. **Documentation**: Must be publicly verifiable

### Mitigation Strategies

1. **Multi-party Ceremony**: 
   - Minimum 100 participants
   - Geographically distributed
   - Public livestream

2. **Circuit Audits**:
   - Formal verification where possible
   - Third-party security review
   - Public disclosure of circuits

3. **Gradual Rollout**:
   - Start with low-value transactions
   - Monitor for anomalies
   - Emergency pause capability

## Development Plan

### Week 1-2: Environment Setup
- Install circom and snarkjs
- Create basic test circuit
- Benchmark proof generation

### Week 3-4: Basic Circuit
- Implement receipt hash verification
- Add signature verification
- Test with sample receipts

### Week 5-6: Integration
- Add to coordinator API
- Create verification contract
- Test settlement flow

### Week 7-8: Trusted Setup
- Plan ceremony logistics
- Prepare ceremony software
- Execute multi-party setup

### Week 9-10: Testing & Audit
- End-to-end testing
- Security review
- Performance optimization

## Next Steps

1. **Immediate**: Set up development environment
2. **Research**: Deep dive into circom best practices
3. **Prototype**: Build minimal viable circuit
4. **Evaluate**: Performance with real receipt data
5. **Decide**: Final technology choice based on testing
