Smart Contract Examples

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import "fhevm/lib/TFHE.sol";
import "fhevm/abstracts/EIP712WithModifier.sol";

/// @title Counter
/// @notice A simple counter contract with encrypted state
/// @dev From Zama FHEVM documentation examples
contract Counter is EIP712WithModifier {
    euint32 private _count;
    address public owner;

    event CounterUpdated(address indexed user);

    constructor() EIP712WithModifier("Counter", "1") {
        owner = msg.sender;
        _count = TFHE.asEuint32(0);
    }

    /// @notice Increment the counter by an encrypted amount
    /// @param encryptedAmount The encrypted amount to add
    function increment(bytes calldata encryptedAmount) 
        external 
        onlySignedPublicKey 
    {
        euint32 amount = TFHE.asEuint32(encryptedAmount);
        _count = TFHE.add(_count, amount);
        emit CounterUpdated(msg.sender);
    }

    /// @notice Get the encrypted counter value
    /// @return The encrypted counter value
    function getCounter() external view returns (bytes memory) {
        return TFHE.reencrypt(_count, msg.sender);
    }

    /// @notice Get decrypted counter value (only owner)
    /// @return The decrypted counter value
    function getCounterDecrypted() external view returns (uint32) {
        require(msg.sender == owner, "Only owner can decrypt");
        return TFHE.decrypt(_count);
    }

    /// @notice Subtract from the counter
    /// @param encryptedAmount The encrypted amount to subtract
    function decrement(bytes calldata encryptedAmount) 
        external 
        onlySignedPublicKey 
    {
        euint32 amount = TFHE.asEuint32(encryptedAmount);
        _count = TFHE.sub(_count, amount);
        emit CounterUpdated(msg.sender);
    }

    /// @notice Reset counter to zero (only owner)
    function reset() external {
        require(msg.sender == owner, "Only owner can reset");
        _count = TFHE.asEuint32(0);
        emit CounterUpdated(msg.sender);
    }
}