Swap ERC7984 to ERC7984

Fully private atomic swap between two confidential ERC7984 tokens. Both input and output amounts remain encrypted throughout—no decryption is needed, ensuring complete privacy from start to finish.

To run this example correctly, make sure the files are placed in the following directories:

• .sol file → <your-project-root-dir>/contracts/

• .ts file → <your-project-root-dir>/test/

This ensures Hardhat can compile and test your contracts as expected.

🔐 FHE API Reference (4 items)

Types: euint64 · externalEuint64

Functions:

• FHE.allowTransient() - Grants TEMPORARY permission (expires at tx end)

• FHE.fromExternal() - Validates and converts external encrypted input using inputProof

SwapERC7984ToERC7984Example.sol

// SPDX-License-Identifier: BSD-3-Clause-Clear
pragma solidity ^0.8.27;

import {FHE, externalEuint64, euint64} from "@fhevm/solidity/lib/FHE.sol";
import {
    IERC7984
} from "@openzeppelin/confidential-contracts/interfaces/IERC7984.sol";
import {ZamaEthereumConfig} from "@fhevm/solidity/config/ZamaConfig.sol";

/**
 * @notice Fully private atomic swap between two confidential ERC7984 tokens.
 *         Both input and output amounts remain encrypted throughout—no decryption
 *         is needed, ensuring complete privacy from start to finish.
 *
 * @dev Encrypted token exchange without intermediate decryption.
 */
contract SwapERC7984ToERC7984Example is ZamaEthereumConfig {
    /// @notice Swap confidential token for another confidential token
    /// @dev fromToken: The token to swap from
    ///      toToken: The token to receive
    ///      amountInput: Encrypted amount to swap
    ///      inputProof: Proof for the encrypted input
    function swapConfidentialForConfidential(
        IERC7984 fromToken,
        IERC7984 toToken,
        externalEuint64 amountInput,
        bytes calldata inputProof
    ) public virtual {
        // 🔍 Check caller is operator for this contract
        require(
            fromToken.isOperator(msg.sender, address(this)),
            "Not authorized operator"
        );

        euint64 amount = FHE.fromExternal(amountInput, inputProof);

        // 📥 Transfer fromToken: user → this contract
        FHE.allowTransient(amount, address(fromToken));
        euint64 amountTransferred = fromToken.confidentialTransferFrom(
            msg.sender,
            address(this),
            amount
        );

        // 📤 Transfer toToken: this contract → user
        // Amount stays encrypted throughout!
        FHE.allowTransient(amountTransferred, address(toToken));
        toToken.confidentialTransfer(msg.sender, amountTransferred);
    }
}

SwapERC7984ToERC7984.ts