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 pywidevine.device import Device, DeviceTypes
from pywidevine.license_protocol_pb2 import SignedMessage, LicenseRequest, ClientIdentification, DrmCertificate, SignedDrmCertificate

from extractor.vendor import Vendor

PARENT = Path(__file__).parent


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', 'igrqajte',
        'ofskesua', 'qllcoacg'
        # Add more as needed for different versions.
    }

    def __init__(self, device: str = None, functions: Path = None, force: bool = False, wvd: 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)

        # Select if create WVD or not
        self.wvd = wvd

        # 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 = {}
        sp = subprocess.run(['adb', '-s', self.device.id, 'shell', 'getprop'], capture_output=True)
        for line in sp.stdout.decode('utf-8').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 = (PARENT / 'keydive.js').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/1225#issuecomment-604181822
        # Iterate through lines starting from the second line (skipping header)
        processes = {}
        sp = subprocess.run(['adb', '-s', self.device.id, 'shell', 'ps'], capture_output=True)
        for line in sp.stdout.decode('utf-8').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' / str(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)

            if self.wvd:
                path_wvd = path / 'device.wvd'
                Device(
                    client_id=client_id.SerializeToString(),
                    private_key=private_key.exportKey('PEM'),
                    type_=DeviceTypes.ANDROID,
                    security_level=3,
                    flags=None
                ).dump(path_wvd)
                self.logger.info('Created WVD: %s', path_wvd)

            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