Note to fellow-HTBers: Only write-ups of retired HTB machines or challenges are allowed.

Challenge info

Inferno [by yuntao ]
Find the flag.

The challenge

We start of by downloading the file and verifying it’s sha256sum with the hash displayed on the challenge page.

$ echo "b178fc8605169bf0d9fd7ba74cd172a193db867d0057be74b5ad6f103d22dc80" | sha256sum -c - OK

We then proceed to unzip this file using the password provided on the challenge page. This will give us a txt file.

$ unzip 
[] inferno.txt password: 
  inflating: inferno.txt

Looking at the content of the file, we see what looks like base64 encoded text.

$ cat inferno.txt 

Decoding the text, we get what looks like random gibberish.

$ base64 -d inferno.txt 

I tried a few things like ROT13, base64 decoding the output again, hexdump, … to no avail.

Getting the flag

Then it struck me: this might be very similar to that Art challenge!

So I went back to the Esoteric programming languages Wikipedia page .
And look at what I found in this list. Do you see the reference with “Inferno”?

Malbolge (the 8th circle of Hell)

The an online interpreter .

Entering the “gibberish” into the interpreter resulted in the flag: