Hello World - Eschaton CTF Writeup

Challenge Info

Field	Details
CTF	Eschaton CTF
Challenge	Hello World
Category	Android / Reverse Engineering

Description

Hello World

Solution

For this challenge, we are given an encrypted Android Backup

To extract the file we would need a password, for that im using the tool - john The steps to use it :

1. androidbackup2john helloworld.dat > helloworld.txt -> this is to identIfy all the parameters required for decryption
2. john --wordlist=/usr/share/dict/rockyou.txt helloworld.txt -> brute forcing the encryption with rockyou.txt which has about 14 million common passwords

The password of the file is hello world, now we can use android backup extractor to extract it
android-backup-unpack -p "hello world" -t ~/Downloads ~/Downloads/helloworld.dat We can inspect the /apps/com.mcsc.helloworld/a/base.APK in Jadx

We see that it app imports sqlcipher and a particulartly interesting string 1s_th1s_th3_fl4g? and also a hidden database is mentioned .notinhere.db We can navigate to /apps/com.mcsc.helloworld/db and do ls -al

We can access .notinhere.db using sqlcipher and try the pragma key as 1s_th1s_th3_fl4g?

The flag is inside the table notes \

Flag

FLAG:esch{he1!0o0o0o0o0_w0r!d}