Overthewire.org Bandit Level 11 -> 12

Guide

Guide for solving Overthewire.org Bandit 11->12

Level Goal

The password for the next level is stored in the file data.txt, where all lowercase (a-z) and uppercase (A-Z) letters have been rotated by 13 positions

Walkthrough

Login to the server using the password obtained from the previous level Bandit level 10 -> 11.

username: bandit11

ssh bandit11@bandit.labs.overthewire.org -p 2220

The file data.txt is located in the home directory.

bandit11@bandit:~$ ls
data.txt

We cat the contents of the file and can see that it does not make any sense when we try to read.

bandit11@bandit:~$ cat data.txt
Gur cnffjbeq vf 5Gr8L4qetPEsPk8htqjhRK8XSP6x2RHh

Going back to the description it mentions characters being rotated, this immediately bring ROT13 to mind.
In a ROT13 cipher characters are rotated 13 places this means

a becomes n
a is 1st letter of the alphabet.
Rotate 13 places 1 + 13 = 14.
14th letter of alphabet is n.

t becomes g
t is the 20th letter of the alphabet.
Rotate 13 places 20 + 13 = 33.
Since 33 is greater then 26 (26 letters in alphabet) we take 26 from 33 to bring it back into the alphabet range.
33 - 26 = 7
7th letter of the alphabet is g.

Full ROT13 mappings

a  ->  n  ||  n  ->  a    
b  ->  o  ||  o  ->  b
c  ->  p  ||  p  ->  c
d  ->  q  ||  q  ->  d
e  ->  r  ||  r  ->  e
f  ->  w  ||  s  ->  f
g  ->  t  ||  t  ->  g
h  ->  u  ||  u  ->  h
i  ->  v  ||  v  ->  i
j  ->  w  ||  w  ->  j
k  ->  x  ||  x  ->  k
l  ->  y  ||  y  ->  l
m  ->  z  ||  z  ->  m

Now with an understanding of ROT13 we can move on and complete the level.

We can use a linux command line tool tr (translate) to translate the rotated characters back to their original position.

bandit11@bandit:~$ cat data.txt
Gur cnffjbeq vf 5Gr8L4qetPEsPk8htqjhRK8XSP6x2RHh

bandit11@bandit:~$ cat data.txt | tr a-zA-Z n-za-mN-ZA-M
The password is 5Te8Y4##########################

Or we can one of many online tools like CyberChef that have graphical interfaces to solve the ROT13 ciphertext.