Flagdroid 147 solves 153 points Easy Category: Reverse Author: m0ney Text: “This app won’t let me in without a secret message. Can you do me a favor and find out what it is?” Download file: an APK Analysis of the app We decompile the application. The validation of the flag is done when you press the button check: 1 2 3 4 5 6 7 8 9 10 11 12 13 public void onClick(View arg10) { TextView tvWrong = (TextView)MainActivity.

I tried TU CTF. I only played 1 or 2 hours and flagged quite a lot: this is an easy CTF, good for beginners. See some very quick write-ups below. Unfortunately I can’t remember the titles of the challenges. Challenge 1 We have a binary to decompile. I use Ghidra and locate a strange function called thisone The printFlag function decodes the flag. I write a program to mimic the decoding:

Cobol OTP Category: Crypto Author: midao Level: easy Solves: 104 Thanks to R. who actually flagged it :) Description To save the future you have to look at the past. Someone from the inside sent you an access code to a bank account with a lot of money. Can you handle the past and decrypt the code to save the future? Attached file A zip is provided with: otp.cob: a program in Cobol out 1 2 Enter your message to encrypt: ���y;dhu��F�]UjhC��-�1T`h&��F�1*T{_���p02J Understanding the Cobol program We understand the Cobol program is performing XOR encryption using a key provided in a keyfille.