def _process_ssh_dss(self, data):
        """Parses ssh-dsa public keys."""
        data_fields = {}
        current_position = 0
        for item in ("p", "q", "g", "y"):
            current_position, value = self._unpack_by_int(data, current_position)
            data_fields[item] = self._parse_long(value)

        q_bits = self._bits_in_number(data_fields["q"])
        p_bits = self._bits_in_number(data_fields["p"])
        if q_bits != self.DSA_N_LENGTH:
            raise InvalidKeyError("Incorrect DSA key parameters: bits(p)=%s, q=%s" % (self.bits, q_bits))
        if self.strict_mode:
            min_length = self.DSA_MIN_LENGTH_STRICT
            max_length = self.DSA_MAX_LENGTH_STRICT
        else:
            min_length = self.DSA_MIN_LENGTH_LOOSE
            max_length = self.DSA_MAX_LENGTH_LOOSE
        if p_bits < min_length:
            raise TooShortKeyError("%s key can not be shorter than %s bits (was %s)" % (self.key_type, min_length, p_bits))
        if p_bits > max_length:
            raise TooLongKeyError(
                "%s key data can not be longer than %s bits (was %s)" % (self.key_type, max_length, p_bits)
            )

        dsa_parameters = DSAParameterNumbers(data_fields["p"], data_fields["q"], data_fields["g"])
        self.dsa = DSAPublicNumbers(data_fields["y"], dsa_parameters).public_key(default_backend())
        self.bits = self.dsa.key_size

        return current_position
Parses ssh-dsa public keys.