Allow the CDM version and fn to be passed via args

Helpers/Device.py

@@ -7,20 +7,18 @@ from Helpers.wv_proto2_pb2 import SignedLicenseRequest
 
 
 class Device:
-    def __init__(self):
+    def __init__(self, dynamic_function_name, cdm_version):
         self.logger = logging.getLogger(__name__)
         self.saved_keys = {}
-        self.frida_script = open(
-            './Helpers/script.js',
-            'r',
-            encoding="utf_8"
-        ).read()
-        self.widevine_libraries = [
-            'libwvhidl.so'
-        ]
+        self.widevine_libraries = ['libwvhidl.so']
         self.usb_device = frida.get_usb_device()
         self.name = self.usb_device.name
 
+        with open('./Helpers/script.js', 'r', encoding="utf_8") as script:
+            self.frida_script = script.read()
+        self.frida_script = self.frida_script.replace(r'${DYNAMIC_FUNCTION_NAME}', dynamic_function_name)
+        self.frida_script = self.frida_script.replace(r'${CDM_VERSION}', cdm_version)
+
     def export_key(self, key, client_id):
         save_dir = os.path.join(
             'key_dumps',
@@ -65,7 +63,9 @@ class Device:
         public_key = root.Msg.ClientId.Token._DeviceCertificate.PublicKey
         key = RSA.importKey(public_key)
         cur = self.saved_keys.get(key.n)
-        self.export_key(cur, root.Msg.ClientId)
+
+        if cur is not None:
+            self.export_key(cur, root.Msg.ClientId)
 
     def find_widevine_process(self, process_name):
         process = self.usb_device.attach(process_name)

Helpers/script.js

@@ -1,4 +1,16 @@
-const CDM_VERSION = ''
+const DYNAMIC_FUNCTION_NAME = '${DYNAMIC_FUNCTION_NAME}';
+const CDM_VERSION = '${CDM_VERSION}';
+
+// These strings are function names that have been succesfully dumped.
+const KNOWN_DYNAMIC_FUNCTION_NAMES = [
+    'rnmsglvj',
+    'polorucp',
+    'kqzqahjq',
+    'pldrclfq',
+    'kgaitijd',
+    'dnvffnze',
+    'cwkfcplc'
+];
 
 // The TextEncoder/Decoder API isn't supported so it has to be polyfilled.
 // Taken from https://gist.github.com/Yaffle/5458286#file-textencodertextdecoder-js
@@ -85,6 +97,8 @@ function prepareKeyRequest(address) {
                     this.ret = args[5];
                     break;
                 default:
+                    const message = 'Defaulting to args[4] for PrepareKeyRequest.'
+                    send('message_info', new TextEncoder().encode(message));
                     this.ret = args[4];
                     break;
             }
@@ -102,22 +116,29 @@ function prepareKeyRequest(address) {
 function hookLibFunctions(lib) {
     const name = lib['name'];
     const baseAddr = lib['base'];
-    const message = 'Hooking ' + name + ' at ' + baseAddr;
+    let message = 'Hooking ' + name + ' at ' + baseAddr;
+    let hookedProvidedModule = false;
+    let funcNames = [];
 
-    send('message_info', new TextEncoder().encode(message))
+    send('message_info', new TextEncoder().encode(message));
 
     Module.enumerateExportsSync(name).forEach(function (module) {
         try {
             let hookedModule;
             if (module.name.includes('UsePrivacyMode')) {
                 disablePrivacyMode(module.address);
-                hookedModule = module.name
+                hookedModule = module.name;
             } else if (module.name.includes('PrepareKeyRequest')) {
                 prepareKeyRequest(module.address);
-                hookedModule = module.name
-            } else if (module.name.match(/^[a-z]+$/)) {
+                hookedModule = module.name;
+            } else if (DYNAMIC_FUNCTION_NAME !== '' && module.name.includes(DYNAMIC_FUNCTION_NAME)) {
                 getPrivateKey(module.address);
-                hookedModule = module.name
+                hookedModule = module.name;
+                hookedProvidedModule = true;
+            } else if (DYNAMIC_FUNCTION_NAME === '' && module.name.match(/^[a-z]+$/)) {
+                getPrivateKey(module.address);
+                hookedModule = module.name;
+                funcNames.push(hookedModule);
             }
 
             if (hookedModule) {
@@ -128,6 +149,19 @@ function hookLibFunctions(lib) {
             console.log("Error: " + e + " at F: " + module.name);
         }
     });
+
+    if (DYNAMIC_FUNCTION_NAME !== '' && !hookedProvidedModule) {
+        const message = "Unable to find '" + DYNAMIC_FUNCTION_NAME + "'";
+        send('message_info', new TextEncoder().encode(message));
+    }
+
+    if (DYNAMIC_FUNCTION_NAME === '') {
+        const possibleFuncNames = KNOWN_DYNAMIC_FUNCTION_NAMES.filter(x => funcNames.includes(x));
+        if (possibleFuncNames.length) {
+            message = "Your function name is most likely: " + "'" + possibleFuncNames.join('\', \'') + "'";
+            send('message_info', new TextEncoder().encode(message));
+        }
+    }
 }
 
 function getModuleByName(lib) {

README.md

@@ -7,19 +7,42 @@ The function parameters can differ between CDM versions. The default is [4] but
 
 * `CDM_VERSION` can be retrieved using a DRM Info app.
 
-## Requirements
+## Requirements:
 Use pip to install the dependencies:
 
 `pip3 install -r requirements.txt`
 
-## Usage
+## Usage:
 
 * Enable USB debugging
 * Start frida-server on the device
 * Execute dump_keys.py
 * Start streaming some DRM-protected content
 
-## Known Working Versions
+The script will hook every function in your 'libwvhidl.so' module by default, effectively brute forcing the private key function name.
+```
+python3 .\dump_keys.py [OPTIONS]
+```
+
+You can pass the function name to hook using the `--function-name` argument.
+```
+python3 .\dump_keys.py --function-name 'polorucp'
+```
+
+The script defaults to `args[4]` if no `--cdm-version` is provided. This will only have an effect if your version is `16.1.0`.
+
+```
+python3 .\dump_keys.py --cdm-version '16.1.0'
+```
+
+## Options:
+```
+    -h, --help                      Print this help text and exit.
+    --cdm-version                   The CDM version of the device e.g. '16.1.0'.
+    --function-name                 The name of the function to hook to retrieve the private key.
+```
+
+## Known Working Versions:
 * Android 9
     * CDM 14.0.0
 * Android 10

dump_keys.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 
+import argparse
 import time
 import logging
 from Helpers.Device import Device
@@ -10,10 +11,17 @@ logging.basicConfig(
     level=logging.DEBUG,
 )
 
-
 def main():
+    parser = argparse.ArgumentParser(description='Android Widevine L3 dumper.')
+    parser.add_argument('--cdm-version', help='The CDM version of the device e.g. \'14.0.0\'', default='14.0.0')
+    parser.add_argument('--function-name', help='The name of the function to hook to retrieve the private key.', default='')
+    args = parser.parse_args()
+
+    dynamic_function_name = args.function_name
+    cdm_version = args.cdm_version
+
     logger = logging.getLogger("main")
-    device = Device()
+    device = Device(dynamic_function_name, cdm_version)
     logger.info('Connected to %s', device.name)
     logger.info('Scanning all processes')