Returns signed data if present in the message

def data(self):
        """
        Returns signed data if present in the message
        """
        # Check if signatire is detached
        if self.detached:
            return None
        bio = Membio()
        if not libcrypto.CMS_verify(self.ptr, None, None, None, bio.bio,
                                    Flags.NO_VERIFY):
            raise CMSError("extract data")
        return str(bio)