Introduction

Had some free time in between lessons and thought I’d do some CTF. Only managed to solve some simple challenges.


Forensics

You Can’t See Me

We are given a pdf file. Opening it gives us 80 pages of nothing or so it may seem… Being a student, one of the secret ways to increase word count of your essays (that I definitely don’t use) is by appending random text below and making them white. This way, the word counter would count more words, but the teacher can’t read those extra words. However, since the text is there, we can find them by CTRL + F and searching for the flag format.

CTRL+FSkillage

Sure enough we are able to find the flag.

P.S Don’t cheat on your assignments…

Cunning Black Cow

We are given a zip file. Unzipping file gives us 2 images. Viewing the Exif of the images gives us what seems to be base64 encoded strings.

One of them decodes to: y0uw@ntk3y?AESe_K@iS3_D3_DuUuU!! The other is unable to be decoded

At this point, I noticed the challenge title, Initials are CBC. The base64 encoded string that we just decoded also has AES capitalise. Further inspection of the string, I realise y0uw@ntk3y?AESe_K@iS3_D3_DuUuU!! happens to be 32 bit in length which is the key size for 256 bit AES. Using an online decoder, we can decrypt the undecodable string.

Result is: bjB0eTB1cjRsQDZPT1BTIQ==

Base64 decoding that gives us: n0ty0ur4l@6OOPS! Wrapping in rooters{}ctf gives us our flag: rooters{n0ty0ur4l@6OOPS!}ctf