Security

How x402 keeps your funds and data safe.

Key Security Properties

Private Key Never Sent

Your private key never leaves your device. The x402 protocol uses signatures, not key transmission:

Client                              Server
  |                                    |
  |  Private key stays here            |
  |  Only signature is sent ---------> |
  |                                    |

Payment Authorization, Not Transfer

You don't send USDC directly. Instead, you sign an authorization that allows a specific recipient to claim a specific amount within a time window.

{
  "from": "your-wallet",
  "to": "service-wallet",
  "value": "1000",
  "validAfter": "1234567890",
  "validBefore": "1234568190"
}

Benefits:

Revocable - Expires if not claimed
Specific - Only the named recipient can claim
Limited - Only the specified amount

EIP-3009 Standard

x402 uses EIP-3009 TransferWithAuthorization, a standard for gasless token transfers:

Widely audited and used
Supported by major stablecoins (USDC, EURC)
Battle-tested in production

EIP-712 Typed Data

Signatures use EIP-712 typed structured data:

Human-readable in wallet signing prompts
Domain-separated to prevent replay attacks
Includes chain ID to prevent cross-chain replay

Threat Model

What x402 Protects Against

Threat	Protection
Key theft during transmission	Private key never sent
Overpayment	Exact amount specified in signature
Replay attacks	Unique nonce per transaction
Cross-chain replay	Chain ID in signature domain
Stale authorizations	Time-bounded validity window
Man-in-the-middle	Cryptographic signature verification

What You Must Protect

Responsibility	How
Private key security	Use secure storage (env vars, secret managers)
Wallet balance	Only fund wallets with needed amounts
Network security	Use HTTPS endpoints

Best Practices

Private Key Storage

Development:

# .env file (git-ignored)
BLOCKRUN_WALLET_KEY=0x...

Production:

# Use secret managers
# AWS Secrets Manager, GCP Secret Manager, etc.

Wallet Hygiene

Use a dedicated wallet - Don't use your main wallet
Fund incrementally - Add USDC as needed
Monitor balance - Set up alerts for low balance

Request Validation

The SDKs validate responses:

# SDK validates:
# - Response came from expected endpoint
# - Payment amount matches quoted price
# - Response is properly formatted

Facilitator Security

The CDP Facilitator (Coinbase Developer Platform) provides:

Feature	Benefit
Signature verification	Ensures only valid payments accepted
Rate limiting	Prevents abuse
Audit logging	Transaction traceability
Multi-sig operations	Enterprise-grade security

FAQ

Can BlockRun steal my funds?

No. BlockRun can only claim the exact amount you authorized for a specific request. Your wallet remains under your control.

What if I sign but the request fails?

If the AI request fails, the payment is not settled. You only pay for successful requests.

Can someone replay my payment?

No. Each payment has a unique nonce that can only be used once.

What if BlockRun's servers are compromised?

Attackers could only claim payments for requests they process. They cannot access your wallet or claim more than authorized amounts.

Audits

EIP-3009 (USDC): Audited by Trail of Bits
x402 Protocol: Open source, community reviewed
CDP Facilitator: Operated by Coinbase with SOC 2 compliance

Reporting Issues

Found a security issue? Please report responsibly:

Do not disclose publicly
Email security concerns to the BlockRun team
Allow time for fixes before disclosure