# Full writeupA detailled writeup can be found [here](https://ihuomtia.onrender.com/umass-rev-free-delivery).
# Summarized Solution- Decompile the apk using `jadx`- Extract a base64 encoded string from `MainActivity.java`, the string is `AzE9Omd0eG8XHhEcHTx1Nz0dN2MjfzF2MDYdICE6fyMa`.- Decode the string and then xor it with the key `SPONGEBOBSPONGEBOBSPONGEBOBSPONGEBOBSPONGEBOB`, then you'll obtain `Part 1: UMASS{0ur_d3l1v3ry_squ1d_`- In the decompiled apk, look for a shared library named `libfreedelivery.so`, decompile it and extract some data that was xored with the byte `0x55`, the xored bytes are `\x30\x36\x3d\x3a\x75\x77\x05\x34\x27\x21\x75\x01\x22\x3a\x6f\x75\x22\x64\x39\x39\x0a\x37\x27\x64\x3b\x32\x0a\x64\x21\x0a\x27\x64\x32\x3d\x21\x0a\x65\x23\x66\x27\x0a\x74\x28\x77\x55`, xor them with `0x55` and you'll obtain `echo "Part Two: w1ll_br1ng_1t_r1ght_0v3r_!}"\x00'`- Put together with the first part, we get the full flag: `UMASS{0ur_d3l1v3ry_squ1d_w1ll_br1ng_1t_r1ght_0v3r_!}`