c# keygen

private KeyState CheckKey(string key) { // key length: 32 chars
    byte[] buffer = new byte[key.Length / 2];
    int num = 0;
    for (int i = 0; i < key.Length; i += 2) {
        try {
            buffer[num] = Convert.ToByte(key.Substring(i, 2), 16);
        } catch {
            return KeyState.InvalidKey;
        }
        num++;
    }
    MemoryStream memoryStream = new MemoryStream();
    CryptoStream cryptoStream = null;
    try {
        cryptoStream = new CryptoStream(memoryStream,
            new TripleDESCryptoServiceProvider().CreateDecryptor(SecretKey, Iv), CryptoStreamMode.Write);
    } catch {
        cryptoStream = null;
        return KeyState.Unknown;
    }
    byte[] arr = null;
    if (cryptoStream != null) {
        try {
            cryptoStream.Write(buffer, 0, buffer.Length);
            cryptoStream.FlushFinalBlock(); // <---- System.Security.Cryptography.CryptographicException: Bad Data.
            memoryStream.Position = 0L;
            arr = memoryStream.ToArray();

            cryptoStream.Close();
            memoryStream.Close();
        } catch {
            return KeyState.InvalidKey;
        }
    }
    if (arr[0] != _licenseVersion[0] || arr[1] != _licenseVersion[1] || arr[2] != _licenseVersion[2] ||
        arr[3] != _licenseVersion[3]) {
        return KeyState.WrongProductKey;
    }

    if (arr[6] != byte_0[arr[4], arr[5]] && arr[9] != byte_0[arr[7], arr[8]]) {
        return KeyState.WrongKey;
    }
    return KeyState.OK;
}