code: def deserialize_footer(stream, verifier=None):
      
      _LOGGER.debug("Starting footer deserialization")
      signature = b""
      if verifier is None:
          return MessageFooter(signature=signature)
      try:
          (sig_len,) = unpack_values(">H", stream)
          (signature,) = unpack_values(">{sig_len}s".format(sig_len=sig_len), stream)
      except SerializationError:
          raise SerializationError("No signature found in message")
      if verifier:
          verifier.verify(signature)
      return MessageFooter(signature=signature)
docs: Deserializes a footer.
  
      :param stream: Source data stream
      :type stream: io.BytesIO
      :param verifier: Signature verifier object (optional)
      :type verifier: aws_encryption_sdk.internal.crypto.Verifier
      :returns: Deserialized footer
      :rtype: aws_encryption_sdk.internal.structures.MessageFooter
      :raises SerializationError: if verifier supplied and no footer found