Parasol - Single Key - Private Tx Example

private_tx.sol

import "sunscreen/src/FHE.sol";

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

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

    // Register a new user with their public key
    // Under single-key model, the user must submit an encryption of zero
    // for their initial balance. Typically this would be accompanied by a ZKP,
    // proving that the amount is indeed zero.
    function register(bytes memory publicKey, bytes memory encryptedZero) public {
        // Don't overwrite someone's balance
        require(balances[publicKey].length == 0);

        // Register the new user with a balance of zero
        balances[publicKey] = encryptedZero;
    } 

    // Execute a private transfer
    // Note: would typically require a ZKP proving amounts are equal and valid and amount <= sender's balance
    function transfer(
        bytes memory senderPk,
        bytes memory receiverPk,
        bytes memory amountSender,
        bytes memory amountReceiver
    ) public {
        balances[senderPk] = fhe.subtractUint256EncEnc(senderPk, balances[senderPk], amountSender);
        balances[receiverPk] = fhe.addUint256EncEnc(receiverPk, balances[receiverPk], amountReceiver);
    }

    /// Retrieve user's encrypted balance
    function balance(bytes memory publicKey) public view returns (bytes memory) {
        return balances[publicKey];
    }
}