How to verify a signature/signed message? Example?

[oliverbytes]

I'm new to Web3 and hope to find an example how to sign and verify messages. Anyone care to share please? Will appreciate any help.

[mrtnetwork]

simple 'personal_message` flutter

      final address = EthereumAddress.fromHex(account);
      String message = "buyer${sellerAdress.toLowerCase()}$orderId";
      final data = await connector.sendCustomRequest(
          method: "personal_sign", params: [message, address.hex, message]);

solidity

       import "@openzeppelin/contracts/utils/Strings.sol";
      using Decryption for bytes32;


    function _veryfiPayment(
        uint64 _orderId,
        address _signer,
        address _receiver,
        bytes memory sign
    ) internal view returns (bool) {
        bytes memory _hash = abi.encodePacked(
            "buyer",
            Strings.toHexString(uint160(_receiver), 20),
            Strings.toString(_orderId)
        );
        bytes32 hash = keccak256(
            abi.encodePacked(
                "\x19Ethereum Signed Message:\n",
                Strings.toString(_hash.length),
                _hash
            )
        );
        address signerAddress = hash.recoverSignedMessage(sign);
        return signerAddress == _signer;
    }
}

library Decryption {
    function recover(
        bytes32 hash,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal pure returns (address) {
        if (
            uint256(s) >
            0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0
        ) {
            return address(0);
        }
        if (v != 27 && v != 28) {
            return address(0);
        }
        address signer = ecrecover(hash, v, r, s);
        return signer;
    }

    function recoverSignedMessage(bytes32 hash, bytes memory message)
        internal
        pure
        returns (address)
    {
        require(message.length == 65);
        bytes32 r;
        bytes32 s;
        uint8 v;
        assembly {
            r := mload(add(message, 0x20))
            s := mload(add(message, 0x40))
            v := byte(0, mload(add(message, 0x60)))
        }
        return recover(hash, v, r, s);
    }
}

for verify in flutter u can use Dart-ECDSA package