This category is a mix of javascript, crypto and zip file recovery. To repair the corrupted zip file, you will need a hex editor (if repairing manually). Otherwise, it's not very time-consuming and you can easily score extra points.
Information
Category Name: DFA2020: MISC
Files:
– just_some_js : 46.2 KB
– this_is_not_js: 321 bytes
– file.zip_broken: 215 bytes
My Recommendations
If you already created the dfa20 working directory:
mkdir Documents/dfa20/misc
If not, create it:
mkdir Documents/dfa20 && mkdir Documents/dfa20/misc
In your VM, open Firefox and download all three files in the “MISC” category to the Working Directory.
node --version
Walkthrough
1. Just some JS (100)
Check out what I can do!
file: just_some_js
The file is a java script file, to run it in your Terminal, you need to use node:
node just_some_js
Answer: flag<what_a_cheeky_language!1!>
2. This is not JS (150)
I’m tired of Javascript. Luckily, I found the grand-daddy of that lame last language!
file: this_is_not_js
I use cat to see the full contents of the file:
cat this_is_not_js
Googling for “programming language punctuation only” takes me to this Wikipedia page. This file appears to be in “Brainf*ck” language. I’m going to one of my favorite websites to decode this. The output is:
Answer: flag<Now_THIS_is_programming>
3. Unzip Me (375)
I zipped flag.txt and encrypted it with the password “password” but I think the header got messed up… You can have the flag if you fix the file.
file: file.zip_broken
From the question we know the following:
The zip contains the file “flag.txt”
The zip is encrypted
The header is corrupted
To recover the zip file, I use this site which explains the structure of PKZip archives very well.
I open the file: zip.broken in Okteta (you can use Cyberchef or any Hex Editor)
I copy all its hex content to a new file, and modify the following values:
0x1400 = PKVersion Needed to Extract
0x0000 = General Bit Purpose Flag (00 means encrypted).
0x0800 = Filename length (flag.txt = 8 bytes).
I save the new file as “test.zip”, and unzip it:
unzip test.zip
##password prompt
password
##read flag
cat flag.txt
Answer: flag<R3ad_th3_spec>
TLDR
– Short section dealing with JavaScript & file recovery.
