def METHOD_NAME(self, secret_key, params64):
    params_dic = self._url_decode64(params64)
    if "Ds_Merchant_Order" in params_dic:
        order = str(params_dic["Ds_Merchant_Order"])
    else:
        order = str(urllib.parse.unquote(params_dic.get("Ds_Order", "Not found")))
    cipher = DES3.new(
        key=base64.b64decode(secret_key), mode=DES3.MODE_CBC, IV=b"\0\0\0\0\0\0\0\0"
    )
    diff_block = len(order) % 8
    zeros = diff_block and (b"\0" * (8 - diff_block)) or b""
    key = cipher.encrypt(str.encode(order + zeros.decode()))
    if isinstance(params64, str):
        params64 = params64.encode()
    dig = hmac.new(key=key, msg=params64, digestmod=hashlib.sha256).digest()
    return base64.b64encode(dig).decode()