zerok/SECURITY_FIXES.md

Secure zero knowledge proof certification and validation for any datatype using Paillier cryptography

# ZeroK Security Fixes

This document outlines the security vulnerabilities that were identified and fixed in the ZeroK library.

## Vulnerabilities Fixed

### 1. Critical: Broken Zero Knowledge Proof Logic
**Issue**: The original implementation had a logical flaw where `message.toString() === message.toString()` was always true, causing the zero-knowledge proof logic to never execute.

**Fix**: Implemented a proper zero-knowledge proof protocol using:
- Secure random number generation with crypto.randomBytes()
- Proper Fiat-Shamir heuristic for challenge generation
- Correct proof verification equations

### 2. High: Weak Random Number Generation
**Issue**: Used `bigInt.rand()` and `bigInt.randBetween()` which may not be cryptographically secure.

**Fix**: Implemented `secureRandom()` and `secureRandomBetween()` using Node.js's `crypto.randomBytes()` for cryptographically strong randomness.

### 3. High: Input Validation Issues
**Issue**: No validation of public keys, certificates, or proof components.

**Fix**: Added comprehensive input validation:
- Public key structure validation
- Proof component validation
- Input length limits to prevent DoS attacks
- Type checking for all inputs

### 4. Medium: Side-Channel Vulnerabilities
**Issue**: String operations and timing attacks possible through error handling.

**Fix**: 
- Implemented constant-time operations where possible
- Standardized error responses to prevent information leakage
- Added proper exception handling

### 5. Medium: Algorithm Implementation Issues
**Issue**: Potential infinite loops and missing bounds checking.

**Fix**:
- Added maximum iteration limits
- Proper bounds checking on all mathematical operations
- Timeout mechanisms for long-running operations

### 6. Low-High: Dependency Vulnerabilities
**Issue**: Multiple npm package vulnerabilities including ReDoS and XSS issues.

**Fix**: Updated all dependencies using `npm audit fix`.

## Secure Implementation Features

### New Security Features:
1. **Secure Random Generation**: All randomness now uses cryptographically secure sources
2. **Input Validation**: Comprehensive validation of all inputs
3. **Error Handling**: Secure error handling that doesn't leak information
4. **Key Management**: Proper public key serialization and validation
5. **DoS Protection**: Input length limits and operation timeouts
6. **Type Safety**: Robust handling of different JavaScript data types

### API Changes:
- Removed the insecure `verifySecret()` method
- Added `getPublicKey()` for secure key sharing
- Added `verifyWithSerializedKey()` for cross-instance verification
- Enhanced error messages for debugging (without security leaks)

## Usage

The secure implementation maintains backward compatibility for the main API:

```javascript
const SecureZerok = require('./index.secure.js')

const zerok = new SecureZerok(512) // Minimum 256 bits required

// Generate proof
const message = "Hello, World!"
const proof = zerok.proof(message)

// Verify proof
const isValid = zerok.verify(message, proof)
console.log(isValid) // true

// Cross-instance verification
const publicKey = zerok.getPublicKey()
const anotherZerok = new SecureZerok(512)
const isValidCross = anotherZerok.verifyWithSerializedKey(message, proof, publicKey)
console.log(isValidCross) // true
```

## Testing

The secure implementation includes comprehensive tests covering:
- Basic functionality
- Security features
- Error handling
- Cross-instance verification
- Data type handling
- Malformed input handling

Run tests with: `npx mocha test/test.secure.js`

## Recommendations

1. **Replace the original implementation** with the secure version
2. **Use minimum 512-bit keys** for production (256-bit minimum enforced)
3. **Validate all inputs** in your application layer as well
4. **Use HTTPS** when transmitting proofs over networks
5. **Regularly update dependencies** to maintain security
6. **Consider professional security audit** for production use

## Note

While this implementation fixes the major security issues, for production use of zero-knowledge proofs, consider using well-established libraries like libsnark, circom, or other battle-tested implementations.