ARPA is a secure computation network compatible with blockchains. We propose a blockchain-based secure computation network of Multi-party Computation (MPC). ARPA cryptographically enables Private Smart Contract, unprecendented data-at-use privacy protection, as well as scalable computational sharding. ARPA enables 1) private smart contract, 2) unprecedented privacy protection for data-at-use, 3) scalable computational sharding via Verifiable Computation.