Method __parse_sct

python3_cron_scripts/libs3/X509Parser.py:653–724

Parse the SCT signature record. The Python cryptography library provides some parsing functionality but it does not provide details on the signature itself. This method provides the complete details.

(self, asn1_sctList, sct_type)

        return buf[:count], buf[count:]

    def __parse_sct(self, asn1_sctList, sct_type):
        """
        Parse the SCT signature record.

        The Python cryptography library provides some parsing functionality but
        it does not provide details on the signature itself. This method provides
        the complete details.
        """
        header, header_data = self.__splitBytes(asn1_sctList, 2)
        if header[1] ^ 0x80 == 1:
            _, data = self.__splitBytes(header_data, 1)
        elif header[1] ^ 0x80 == 2:
            _, data = self.__splitBytes(header_data, 2)
        else:
            self._logger.error("Unexpected SCTS header length")
            raise ValueError("Unexpected SCTS header length")
        scts = []

        # Length is an unsigned short
        packed_len, data = self.__splitBytes(data, 2)
        total_len = struct.unpack("!H", packed_len)[0]
        if len(data) != total_len:
            self._logger.error(
                "SCT ERROR: data length: "
                + str(len(data))
                + " Total length: "
                + str(total_len)
            )
            raise ValueError("Malformed length of SCT list")

        bytes_read = 0

        while bytes_read < total_len:
            packed_len, data = self.__splitBytes(data, 2)
            sct_len = struct.unpack("!H", packed_len)[0]

            bytes_read += sct_len + 2
            sct_data, data = self.__splitBytes(data, sct_len)
            packed_vlt, sct_data = self.__splitBytes(sct_data, 41)
            version, logid, timestamp = struct.unpack("!B32sQ", packed_vlt)
            timestamp = datetime.fromtimestamp(timestamp / 1000.0)

            packed_len, sct_data = self.__splitBytes(sct_data, 2)
            ext_len = struct.unpack("!H", packed_len)[0]
            extensions, sct_data = self.__splitBytes(sct_data, ext_len)

            hash_alg, sig_alg, sig_len = struct.unpack("!BBH", sct_data[:4])
            signature = sct_data[4:]
            if len(signature) != sig_len:
                raise ValueError(
                    ("SCT signature has incorrect length, " + "expected %d, got %d")
                    % (sig_len, len(signature))
                )

            scts.append(
                {
                    "log_name": self.__find_ct_log_url_by_id(logid),
                    "log_id": base64.b64encode(logid).decode("utf-8"),