Legu Unpacker

Scripts to unpack Android applications protected by Tencent Legu. It only works with versions 4.1.0.15 and 4.1.0.18 of Legu.

Blog post: https://www.romainthomas.fr/post/a-glimpse-into-tencents-legu-packer/

Overview

The original DEX files are located in assets/0OO00l111l1l with the following layout:

One can find the details of this structure in the Kaitai file: legu_packed_file.ks

The hashmap embedded in the second part is described in the legu_hashmap.ks file:

pylegu

pylegu contains the Python bindings to decrypt and uncompress the data embedded in assets/0OO00l111l1l.

To compile and install pylegu:

$ cd pylegu
$ python3.7 ./setup.py build -j4 install --user
$ python -c "import pylegu"

One could also use jap/pyucl to decompress the data and aguinet/dragonffi to bind the custom implementation of XTEA.

Get Started

The sample com.intotherain.voicechange.apk is a suspicious application that can be unpacked as follows:

$ python ./unpack.py ./samples/com.intotherain.voicechange.apk

[+] Legu version: 4.1.0.15
[+] Password is 'IPk2Hw7AKTuIQBlc'
[+] Number of dex files: 1
[+] Unpacking #1 DEX files ...
[+] dex 0 compressed size:   0x1619a3
[+] dex 0 uncompressed size: 0x5671f8

[+] Unpacking #1 hashmap ...
[+] hashmap 0 compressed size:   0x4399c
[+] hashmap 0 uncompressed size: 0x95558

[+] Unpacking #1 packed methods ...
[+] packed methods 0 compressed_size:   0xf4636
[+] packed methods 0 uncompressed_size: 0x1e3072

[+] Stage 2: Patching DEX files
[+] Unpacked APK: unpacked.apk

The unpacked DEX files are located in the unpacked.apk file.

Requirements

• Python >= 3.7
• Kaitai Struct
• LIEF
• pylegu