Not working, entry point not found?

[weltmeyer]

I have an apk here where it is not going to decrypt. Its running until

preparing->ready.

from my observations, it just never finds the "bytesC.start" part. i have also seen that my apk has two classes (classes.dex and classes2.dex) files.

Could you help me with this?

[JadinAndrews]

Sorry can't help you, but my APK also had two classes.dex files, but ti_recover worked flawlessly on it so I don't think that is your problem

[creador]

Are you sure @weltmeyer that the APK was made with Appcelerator Titanium ? Do you know the versión ? It's being already 4 years since I made this app, so maybe it doesn't work with the newest versions de Titanium.

[hacker1024]

AssetCryptImpl.java has changed. Here are the new relevant bits:

public class AssetCryptImpl implements AssetCrypt {
    private static final String BIN_EXT = ".bin";
    private static final Collection<String> assets = new ArrayList(Arrays.asList(new String[]{"Resources/source1.js", "Resources/source2.js", "etc."}));
    private static byte[] salt = new byte[]{(byte) -39, (byte) -51, (byte) 24, (byte) 15, (byte) 102, (byte) 98, (byte) 103, (byte) 67, (byte) -4, (byte) 45, (byte) 24, (byte) -41, (byte) -88, (byte) -54, (byte) 116, (byte) 101};

    private static InputStream getAssetStream(String str) {
        if (!assets.contains(str)) {
            return null;
        }
        if (!str.endsWith(BIN_EXT)) {
            str = str + BIN_EXT;
        }
        try {
            Cipher instance = Cipher.getInstance("AES/CBC/PKCS5Padding");
            instance.init(2, new SecretKeySpec(Binding.getKey(salt), "AES"), new IvParameterSpec(salt));
            return new CipherInputStream(KrollAssetHelper.getAssetManager().open(str), instance);
        } catch (Exception e) {
            Log.e(TAG, "Could not decrypt '" + str + "'");
            Log.e(TAG, e.toString());
            return null;
        }
    }
}

Here are the things to note:

• Encrypted resources (including the JavaScript code) are declared in the assets collection. The encrypted filenames are calculated by appending the BIN_EXT value to the entries.
• Assets are encrypted with AES/CBC/PKCS5Padding, using a key provided by the native "cloak" library and an IV generated with a hardcoded salt.

To obtain the encryption key, I first attempted analysing the native library. Unfortunately, my assembly skills were not good enough to decode the key generation code.

Instead, the Java Binding.getKey can be intercepted. Using apktool, I decompiled the app, and found the following in AssetCryptImpl.smali:

sget-object v4, Lorg/kosher/app/AssetCryptImpl;->salt:[B
invoke-static {v4}, Lti/cloak/Binding;->getKey([B)[B
move-result-object v4

This is the part of bytecode that obtains the key from the native library and stores it in a register (v4). To obtain this key, I added the following code directly after it:

invoke-static {v4}, Ljava/util/Arrays;->toString([B)Ljava/lang/String; # Convert the key to a string
move-result-object v5 # Save the string in register v5
invoke-static {v5, v5}, Landroid/util/Log;->wtf(Ljava/lang/String;Ljava/lang/String;)I # Log the key in the logcat WTF channel

This prints the key to log cat's WTF channel. The key is used as the tag because no other registers are free at this time to store a tag in.

Once the key is obtained, decrypting the resources is a trivial matter:

for file in $(find . -name '*.bin')
do
  openssl enc -d -aes-128-cbc -K <KEY_HEX> -iv <SALT_HEX> -in "$file" -out "${file//.bin}"
done

I hope this helps!

[j4k0xb]

@hacker1024 I reverse engineered libti.cloak.so (android) and ti.cloak-linux-x64.node (pc bindings)

bindings.js (https://github.com/tidev/titanium_mobile/blob/master/support/ti.cloak.zip) contains this function

/**
 * Synchrounously set key in platform 'ti.cloak' libraries for functioning runtime decryption.
 *
 * @param {string} platform Platform of libraries to process.
 * @param {string[]} archs Array for architectures supported by the platform.
 * @param {string} destination Destination for processed libraries to be stored.
 */
setKeySync(platform, archs, destination) {
  if (platform === 'android') {
    for (const arch of archs) {
      // Load stub library into buffer and set key, throws exception upon failure.
      const buffer = _fsExtra.default.readFileSync(_path.default.join(__dirname, 'android', arch, 'libti.cloak.so'));

      Binding.setKey(buffer, this.key, this.salt); // Write buffer to target destination.

      const target = _path.default.join(destination, arch, 'libti.cloak.so');

      _fsExtra.default.ensureDirSync(_path.default.dirname(target));

      _fsExtra.default.writeFileSync(target, buffer);
    }
  }
}

which writes a fixed block of 64 bytes in all libti.cloak.so files on each compile:

the block contains a xor key (combine with the salt to get the AES key) and is split in 4 parts:

... putting it all together:

const salt = Buffer.from('ddce8e80f1cf129a63224e719496d4dd', 'hex'); // from your AssetCryptImpl
const lib = fs.readFileSync('./lib/arm64-v8a/libti.cloak.so'); // extracted from your apk

const baseOffset = 0x2008;
const randomOffset = lib.readUint8(baseOffset + 0x3e);
const xor = Buffer.concat([
  lib.subarray(baseOffset + 1, baseOffset + 5),
  lib.subarray(baseOffset + randomOffset, baseOffset + randomOffset + 4),
  lib.subarray(baseOffset + 0xf, baseOffset + 0xf + 4),
  lib.subarray(baseOffset + 0x1e, baseOffset + 0x1e + 4),
]);
const key = salt.map((byte, i) => byte ^ xor[i]).toString('hex');
console.log(key);