Just a few hours before “cd year-2023” or “sudo apt install year-2023” if you’d prefer, I participated in an awesome CTF competition organized by UDOM CYBER CLUB.
I solved a few challenges ranging from: OSINT, Forensics, Cryptography, Steganography to Web. Let’s take a look.
1. Cryptography
Challenge: R54
We are given a ct.txt file and a challenge.py file that is supposed to help us get the flag.
This is what was in the files.
ct.txt
challenge.py
As you know RSA algorithm is an asymmetric cryptography algorithm.
Asymmetric simply means it works on two different keys i.e. Public Key and Private Key.
One key is used for encryption while the other is used for decryption. If one key is used to encrypt data, the other key decrypts, and vice versa. This ensures data confidentiality and integrity(depending with which key you start with). RSA is usually based on exactly two prime numbers.
Okay, So I went ahead to use the python challenge file and landed on some “modulus invertibility error” which I did not want to debug(It’s end of year, Gotta be somewhere making resolutions)
I tried an online rsa deciphering tool(here).
From the ct file we have n, e, and ct.
In RSA: n is usually the modulus, e is the encryption exponent: ct was our cypher message.
Feeding this details on the site gave the flag: flag{usa_e_piu_grandi}
2. OSINT
Challenge: Place
We are given an image file “maporomoko.jpg”
Headed over to https://tineye.com/ and did an image reverse search.
Got the name of the waterfall. Googled first result out “Kasanga_Rukwa Region”
And Google did the rest: UDOM{Rukwa}
3. Forensics
Challenge: file
We have flag.zip file that extracts to myfile.pdf
While expecting something, opening the file as pdf was not possible.
I decided to confirm the file type which turned to be an audio file.
Opened it with Audacity only to find myself dancing to morse code.
Quickly uploaded the file to an online morse code decoder. Link here
I replayed a few times just to be sure. UDOM{M0RS3S0UND5B3TT3R1NMIL1TAR13S}
4. Steganography
Challenge 1: Starting point
We are given a pdf file which when opened, we see:
We say ‘buda’ in Kenya, hehe
Tried using steghide to extract hidden files but was prompted with a passphrase. Trying a simple brute force with pdfcrack suggested no encryption.
After running around, I found this site(here), uploaded the file and checked the parsed files.
Challenge 2: Simple stego
This CTF also featured WindowsXP as a png file. Viewing the image shows some blurred markings on the top left corner.
Zooming in brings it better.
UDOM{BR1LL14NT_5T4RT5_H3R3}
5. Web
Challenge 1: Turaco
We have a site which shows nothing when visited. I checked the “page source” and found this.
Decrypted the decimal values in pass variable only to be told: “Uo ni uwongo bhanaa uwongo” — That’s not true man!
I just learnt password in Swahili is called msimbo or is it sambo?(It’s msimbo; Thanks to Stuxkyle) There are ‘sambo’ values in hex down here.
Pasting the hex from the function to Cyberchef we get decimals that when added a decimal recipe give us the flag.
UDOM{1ts_an_0m3n}
Challenge 2: Two-step-snake
We have a site which when visited shows nothing.
Viewing the source code reveals a url encoded string within a unescape function.
Did a double url decode with cyberchef and decrypted the resulting decimal values to get the password.
The CTF was really awesome though didn’t get enough time for it.
Came back later on to find the CTF had ended!
Oh! and again, there are many ways of killing a rat!
Happy Hacking.