KeyDive/extractor/cdm.py

import json
import logging
import re
import subprocess
from pathlib import Path

import xmltodict
import frida
from frida.core import Device, Session, Script
from Cryptodome.PublicKey import RSA

from extractor.license_protocol_pb2 import SignedMessage, LicenseRequest, ClientIdentification, DrmCertificate, SignedDrmCertificate
from extractor.vendor import Vendor

SCRIPT_PATH = Path(__file__).parent / 'script.js'


class Cdm:
    """
    Manages the capture and processing of DRM keys from a specified device using Frida to inject custom hooks.
    """
    OEM_CRYPTO_API = {
        # Mapping of function names across different API levels (obfuscated names may vary).
        'rnmsglvj', 'polorucp', 'kqzqahjq', 'pldrclfq', 'kgaitijd',
        'cwkfcplc', 'crhqcdet', 'ulns', 'dnvffnze', 'ygjiljer',
        'qbjxtubz', 'qkfrcjtw', 'rbhjspoh', 'zgtjmxko'
        # Add more as needed for different versions.
    }

    def __init__(self, device: str = None, functions: Path = None, force: bool = False):
        self.logger = logging.getLogger('Cdm')
        self.functions = functions
        self.running = True
        self.keys = {}
        # Select device based on provided ID or default to the first USB device.
        self.device: Device = frida.get_device(id=device, timeout=5) if device else frida.get_usb_device(timeout=5)
        self.logger.info('Device: %s (%s)', self.device.name, self.device.id)

        # Obtain device properties
        self.properties = self._fetch_device_properties()

        self.sdk_api = self.properties['ro.build.version.sdk']
        self.logger.info('SDK API: %s', self.sdk_api)
        self.logger.info('ABI CPU: %s', self.properties['ro.product.cpu.abi'])

        # Load the hook scrip
        self.script = self._prepare_hook_script()
        self.logger.info('Script loaded successfully')

        # Determine vendor based on device SDK API
        vendor_api = self._prepare_vendor_api(force=force)
        self.vendor = Vendor.from_sdk_api(vendor_api)

        # Update script for specific vendor API, if necessary
        if vendor_api != self.sdk_api:
            self.sdk_api = vendor_api
            self.script = self._prepare_hook_script()
            self.logger.info('Script updated for vendor API')

    def _fetch_device_properties(self) -> dict:
        """
        Retrieves system properties from the connected device using ADB shell commands.
        """
        # https://source.android.com/docs/core/architecture/configuration/add-system-properties?#shell-commands
        properties = {}
        for line in subprocess.getoutput(f'adb -s "{self.device.id}" shell getprop').splitlines():
            match = re.match(r'\[(.*?)\]: \[(.*?)\]', line)
            if match:
                key, value = match.groups()
                # Attempt to cast numeric and boolean values to appropriate types
                try:
                    value = int(value)
                except ValueError:
                    if value.lower() in ('true', 'false'):
                        value = value.lower() == 'true'
                properties[key] = value
        return properties

    def _prepare_hook_script(self) -> str:
        """
        Prepares the Frida hook script, injecting dynamic content like SDK API and selected functions.
        """
        content = SCRIPT_PATH.read_text(encoding='utf-8')
        selected = self._select_functions() if self.functions else {}

        # Replace placeholders in script template
        replacements = {
            '${SDK_API}': str(self.sdk_api),
            '${OEM_CRYPTO_API}': json.dumps(list(self.OEM_CRYPTO_API)),
            '${SYMBOLS}': json.dumps(list(selected.values())),
        }

        for placeholder, real_value in replacements.items():
            content = content.replace(placeholder, real_value)

        return content

    def _select_functions(self) -> dict:
        """
        Parses the provided XML functions file to select relevant functions.
        """
        if not self.functions.is_file():
            raise FileNotFoundError('Functions file not found')

        try:
            program = xmltodict.parse(self.functions.read_bytes())['PROGRAM']
            addr_base = int(program['@IMAGE_BASE'], 16)
            functions = program['FUNCTIONS']['FUNCTION']

            # Find a target function from a predefined list
            target = next((f['@NAME'] for f in functions if f['@NAME'] in self.OEM_CRYPTO_API), None)

            # Extract relevant functions
            selected = {}
            for func in functions:
                name = func['@NAME']
                args = len(func.get('REGISTER_VAR', []))

                # Add function if it matches specific criteria
                if name not in selected and (
                        name == target
                        or any(keyword in name for keyword in ['UsePrivacyMode', 'PrepareKeyRequest'])
                        or (not target and re.match(r'^[a-z]+$', name) and args >= 6)
                ):
                    selected[name] = {'name': name, 'address': hex(int(func['@ENTRY_POINT'], 16) - addr_base)}
            return selected
        except Exception:
            pass
        raise ValueError('Failed to extract functions from Ghidra')

    def enumerate_processes(self) -> dict:
        """
        Lists processes running on the device, returning a mapping of process names to PIDs.
        """
        # https://github.com/frida/frida/issues/2593
        # Iterate through lines starting from the second line (skipping header)
        processes = {}
        for line in subprocess.getoutput(f'adb -s "{self.device.id}" shell ps').splitlines()[1:]:
            try:
                line = line.split()  # USER,PID,PPID,VSZ,RSS,WCHAN,ADDR,S,NAME
                name = ' '.join(line[8:]).strip()
                name = name if name.startswith('[') else Path(name).name
                processes[name] = int(line[1])
            except Exception:
                pass

        return processes

    def _prepare_vendor_api(self, force: bool = False) -> int:
        """
        Determines the most compatible vendor API version based on device processes.
        """
        if force:
            self.logger.warning('Using default vendor due to force flag')
            return self.sdk_api

        # Check if forcing is not enabled and enumerate processes
        details: [int] = []
        processes = self.enumerate_processes()
        for k, v in Vendor.SDK_VERSIONS.items():
            pid = processes.get(v[2])
            if pid:
                self.logger.debug('Analysing... (%s)', v[2])
                session: Session = self.device.attach(pid)
                script: Script = session.create_script(self.script)
                script.load()
                if script.exports_sync.getlibrary(v[3]):
                    details.append(k)
                session.detach()

        # If no compatible versions found
        if details:
            # Find the closest SDK version to the current one, preferring lower matches in case of a tie.
            sdk_api = min(details, key=lambda x: abs(x - self.sdk_api))

            # Adjust SDK version if it exceeds the maximum supported version
            if sdk_api == Vendor.SDK_MAX and self.sdk_api > Vendor.SDK_MAX:
                sdk_api = self.sdk_api
            elif sdk_api != self.sdk_api:
                self.logger.warning('Using non-default Widevine version for SDK %s', sdk_api)

            return sdk_api

        raise EnvironmentError('Unable to detect Widevine, see: https://github.com/hyugogirubato/KeyDive/blob/main/docs/PACKAGE.md#drm-info')

    def _process_message(self, message: dict, data: bytes) -> None:
        """
        Handles messages received from the Frida script.
        """
        logger = logging.getLogger('Script')
        level = message.get('payload')

        if isinstance(level, int):
            # Process logging messages from Frida script
            logger.log(level=level, msg=data.decode('utf-8'))
            if level in (logging.FATAL, logging.CRITICAL):
                self.running = False
        elif level == 'device_info':
            if data:
                self._extract_device_info(data)
            else:
                logger.critical('No data for device info, invalid argument position')
                self.running = False
        elif level == 'private_key':
            self._extract_private_key(data)

    def _extract_private_key(self, data: bytes) -> None:
        """
        Extracts and stores the private key from the provided data.
        """
        key = RSA.import_key(data)
        key_id = key.n
        if key_id not in self.keys:
            self.keys[key_id] = key
            self.logger.debug('Retrieved key: \n\n%s\n', key.exportKey('PEM').decode('utf-8'))

    def _extract_device_info(self, data: bytes) -> None:
        """
        Extracts device information and associated private keys, storing them to disk.
        """
        # https://github.com/devine-dl/pywidevine
        signed_message = SignedMessage()
        signed_message.ParseFromString(data)

        license_request = LicenseRequest()
        license_request.ParseFromString(signed_message.msg)

        client_id: ClientIdentification = license_request.client_id

        signed_drm_certificate = SignedDrmCertificate()
        drm_certificate = DrmCertificate()

        signed_drm_certificate.ParseFromString(client_id.token)
        drm_certificate.ParseFromString(signed_drm_certificate.drm_certificate)

        public_key = drm_certificate.public_key
        key = RSA.importKey(public_key)
        key_id = key.n

        private_key = self.keys.get(key_id)
        if private_key:
            path = Path() / 'device' / self.device.name / 'private_keys' / str(drm_certificate.system_id) / str(key_id)[:10]
            path.mkdir(parents=True, exist_ok=True)
            path_client_id = path / 'client_id.bin'
            path_private_key = path / 'private_key.pem'

            path_client_id.write_bytes(data=client_id.SerializeToString())
            path_private_key.write_bytes(data=private_key.exportKey('PEM'))

            self.logger.info('Dumped client ID: %s', path_client_id)
            self.logger.info('Dumped private key: %s', path_private_key)
            self.running = False
        else:
            self.logger.warning('Failed to intercept the private key')

    def hook_process(self, pid: int) -> bool:
        """
        Hooks into the specified process to intercept DRM keys.
        """
        session: Session = self.device.attach(pid)
        script: Script = session.create_script(self.script)
        script.on('message', self._process_message)
        script.load()

        library_info = script.exports_sync.getlibrary(self.vendor.library)
        if library_info:
            self.logger.info('Library: %s (%s)', library_info['name'], library_info['path'])

            # Check if Ghidra XML functions loaded
            if self.sdk_api > 33:
                if not self.functions:
                    raise AttributeError('For SDK API > 33, specifying "functions" is required, see: https://github.com/hyugogirubato/KeyDive/blob/main/docs/FUNCTIONS.md')
            elif self.functions:
                self.logger.warning('The "functions" attribute is deprecated for SDK API < 34')

            return script.exports_sync.hooklibrary(library_info['name'])
        return False