@bsv/sdk/docs/concepts/trust-model.md

BSV Blockchain Software Development Kit

# Trust Model

Understanding the security assumptions and trust relationships in BSV TypeScript SDK applications.

## Core Trust Principles

The SDK is designed around minimizing trust requirements:

### Trustless Verification

- **Cryptographic Proofs**: Verify transactions mathematically
- **SPV Security**: Validate without trusting third parties
- **Self-Sovereign**: Users control their own keys and data

### Minimized Dependencies

- **Zero External Dependencies**: Reduces attack surface
- **Self-Contained**: All cryptographic operations built-in
- **Auditable**: Open source and transparent implementation

## Trust Relationships

### User Trust

Users must trust:

- **The SDK Code**: Open source and auditable
- **Their Wallet**: Manages private keys securely
- **Their Device**: Secure execution environment

### Network Trust

Applications rely on:

- **Bitcoin Network**: Honest majority of miners
- **Chain Trackers**: Provide accurate blockchain data
- **SPV Assumptions**: Valid merkle proofs and headers

### Service Trust

Optional trust relationships:

- **Wallet Providers**: If using hosted wallets
- **ARC Services**: For transaction broadcasting
- **Overlay Services**: For additional functionality

## Security Assumptions

### Cryptographic Security

- **secp256k1**: Elliptic curve is secure
- **SHA-256**: Hash function is collision-resistant
- **ECDSA**: Digital signature scheme is unforgeable
- **Random Number Generation**: Entropy source is secure

### Network Security

- **Proof of Work**: Mining provides security
- **Longest Chain**: Honest chain has most work
- **Block Finality**: Deep confirmations prevent reorganization
- **Network Connectivity**: Access to honest nodes

## Risk Mitigation

### Key Management

```typescript
// Minimize private key exposure
const wallet = new WalletClient() // Keys stay in wallet

// Avoid direct key handling
// const privateKey = PrivateKey.fromString() // Higher risk
```

### Transaction Verification

```typescript
// Always verify important transactions
const isValid = await transaction.verify(chainTracker, {
  merkleProof: proof,
  blockHeader: header
})
```

### Multiple Sources

```typescript
// Use multiple chain trackers
const config = {
  chainTracker: {
    primary: 'WhatsOnChain',
    fallbacks: ['GorillaPool', 'TAAL']
  }
}
```

## Threat Model

### Attacks to Consider

- **Private Key Compromise**: Secure key storage
- **Man-in-the-Middle**: Use HTTPS and verify certificates
- **Service Downtime**: Implement fallback mechanisms
- **Double Spending**: Wait for confirmations
- **Replay Attacks**: Use unique transaction IDs

## Application Design

### Security-First Design

```typescript
// Validate all inputs
function processTransaction(txHex: string) {
  if (!isValidHex(txHex)) {
    throw new Error('Invalid transaction hex')
  }
  
  const tx = Transaction.fromHex(txHex)
  // Process verified transaction
}
```

### Error Handling

```typescript
// Handle trust failures gracefully
try {
  const result = await chainTracker.getTransaction(txid)
} catch (error) {
  // Fallback to alternative source
  const backup = await fallbackTracker.getTransaction(txid)
}
```

## Next Steps

- Review [Key Management](./key-management.md) security practices
- Understand [SPV Verification](./spv-verification.md) assumptions
- Learn about [Wallet Integration](./wallet-integration.md) trust models