verify.sol

pragma solidity >=0.7.0 <0.9.0;

import "github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v3.3/contracts/cryptography/ECDSA.sol";
import "github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v3.3/contracts/utils/ReentrancyGuard.sol";

contract UniDirectionalPaymentChannel is ReentrancyGuard {
    
    // ...

    function _verify(uint _amount, bytes memory _sig) private view returns (bool) {
        return _getEthSignedHash(_amount).recover(_sig) == sender;
    }

    function verify(uint _amount, bytes memory _sig) external view returns (bool) {
        return _verify(_amount, _sig);
    }
    
    // ...

}