docs: def sign_raw_data(raw_data, privatekey_hex):
      """
      Sign a string of data.
      Returns signature as a base64 string
      """
      if not isinstance(raw_data, (str, unicode)):
          raise ValueError("Data is not a string")
  
      raw_data = str(raw_data)
  
      si = ECSigner(privatekey_hex)
      si.update(raw_data)
      return si.finalize()