Parasol - Network Key - Private Tx Example

private_tx.sol

import "sunscreen/src/FHE.sol";

contract PrivateTxExample {
    // Encrypted balances
    mapping(address => bytes) balances;

    constructor() {
        // Instantiate our FHE subcontract
        fhe = new FHE();
    }

    // Register a new user
    function register() public {
        // Don't overwrite user's balance
        require(balances[msg.sender].length == 0);

        // Register the new user with a balance of zero
        // Here we encrypt under the network key!
        balances[msg.sender] = fhe.encryptUint256(fhe.networkPublicKey(), 0);
    } 

    // Execute a private transfer
    // Note: would typically require a ZKP proving amount <= sender's balance
    function transfer(
        address receiver,
        bytes memory amount,
    ) public {
        balances[msg.sender] = fhe.subtractUint256EncEnc(fhe.networkPublicKey(), balances[msg.sender], amount);
        balances[receiver] = fhe.addUint256EncEnc(fhe.networkPublicKey(), balances[receiver], amount);
    }

    // Retrieve user's balance, encrypted under their own key
    function balance(bytes memory publicKey) public view returns (bytes memory) {
        return fhe.reencryptUint256(publicKey, balances[msg.sender]);
    }
}