Blockchain Infrastructure

Why Blockchain?

Sardis uses stablecoins (USDC) as a settlement rail, not as a product feature. Blockchain gives us three things that traditional payment rails cannot:

• Non-custodial by design: funds live in smart contract wallets, not our bank account. No trust assumption needed.
• Programmable money: spending policies are enforced on-chain. Rules cannot be bypassed, even by us.
• Real-time settlement: no T+2 delays. Payments settle in seconds, not days.

Note: End users never interact with blockchain directly. Sardis abstracts all complexity. Your agents pay in dollars, and we handle the infrastructure.

Supported Chains

Sardis executes all transactions on Base -- the lowest-cost, highest-throughput L2 with native USDC support. Agents can fund wallets from any supported chain via CCTP v2 cross-chain transfers, which automatically consolidate USDC to Base.

Execution vs Funding: All payment execution and smart contract interactions happen on Base. Multi-chain support refers to funding -- agents can receive USDC from Ethereum, Polygon, Arbitrum, or Optimism, and it arrives on Base automatically via Circle's CCTP v2.

Execution Chain

Funding Chains (via CCTP v2)

Send USDC from any of these chains to fund your Sardis agent wallet. Funds are automatically bridged to Base.

MPC Custody (Turnkey)

Sardis uses Multi-Party Computation (MPC) via Turnkey for key management. This means:

• No single point of failure: private keys are split across multiple parties. No single entity (including Sardis) can sign transactions alone.
• Non-custodial: you retain full ownership. Sardis never has access to your funds.
• Agent-compatible: MPC signing does not require 2FA, seed phrases, or hardware wallets. Agents can sign transactions programmatically while maintaining security.

Smart Contract Wallets

Each agent wallet is backed by a Safe Smart Account (v1.4.1) deployed on Base. The wallet enforces on-chain spending policies:

// SardisAgentWallet.sol: Key features
contract SardisAgentWallet {
    address public owner;
    address public agent;
    uint256 public dailyLimit;
    uint256 public perTransactionLimit;

    function executePayment(
        address token,
        address recipient,
        uint256 amount,
        bytes calldata purpose
    ) external onlyAgent withinLimits(amount) { ... }

    function updateLimits(uint256 daily, uint256 perTx)
        external onlyOwner { ... }

    function freeze() external onlyOwner { ... }
}

ERC-4337 Account Abstraction

Sardis uses ERC-4337 (Account Abstraction) to enable gasless transactions for agents:

• No gas tokens needed: agents do not need ETH to pay for transaction fees. Sardis sponsors gas via Circle Paymaster.
• Bundled transactions: multiple operations can be batched into a single transaction for efficiency.
• Social recovery: wallet recovery without seed phrases, using guardian-based recovery mechanisms.

ERC-4337 account abstraction is live on Base via Circle Paymaster for gasless USDC transactions.

Stablecoins as Payment Rails

Sardis uses stablecoins (primarily USDC by Circle) as the settlement layer. Stablecoins are dollar-pegged digital currencies that combine the programmability of blockchain with the stability of fiat currency.

Why USDC?

• Fully backed by US dollar reserves
• Regulated by Circle (US-based)
• $30B+ in circulation
• Native on all supported chains
• Instant settlement (no T+2)

Fiat On/Off Ramp

• Fund wallets from bank accounts (ACH/wire) via Coinbase Onramp
• Automatic USD to USDC conversion
• Withdraw to bank anytime
• Users only see dollar amounts
• No crypto knowledge required

Escrow and Settlement

The escrow system provides trustless escrow for agent-to-merchant payments using Circle RefundProtocol:

• Lock funds: when an agent initiates a payment, funds are locked in escrow
• Verify delivery: the merchant confirms delivery or the service is rendered
• Release or refund: funds are released to the merchant or refunded to the agent
• Dispute resolution: time-locked disputes with owner arbitration