Level Info
ROT13 is a simple substitution cipher.
Substitution ciphers are a simple replacement algorithm. In this example of a substitution cipher, we will explore a ‘monoalphebetic’ cipher. Monoalphebetic means, literally, “one alphabet” and you will see why.
This level contains an old form of cipher called a ‘Caesar Cipher’. A Caesar cipher shifts the alphabet by a set number. For example:
plain: a b c d e f g h i j k ...
cipher: G H I J K L M N O P Q ...
In this example, the letter ‘a’ in plaintext is replaced by a ‘G’ in the ciphertext so, for example, the plaintext ‘bad’ becomes ‘HGJ’ in ciphertext.
The password for level 3 is in the file krypton3. It is in 5 letter group ciphertext. It is encrypted with a Caesar Cipher. Without any further information, this cipher text may be difficult to break. You do not have direct access to the key, however you do have access to a program that will encrypt anything you wish to give it using the key. If you think logically, this is completely easy.
One shot can solve it!
Have fun.
Additional Information:
The encrypt binary will look for the keyfile in your current working
directory. Therefore, it might be best to create a working direcory in /tmp
and in there a link to the keyfile. As the encrypt binary runs setuid
krypton3, you also need to give krypton3 access to your working directory.
Here is an example:
krypton2@melinda:~$ mktemp -d
/tmp/tmp.Wf2OnCpCDQ
krypton2@melinda:~$ cd /tmp/tmp.Wf2OnCpCDQ
krypton2@melinda:/tmp/tmp.Wf2OnCpCDQ$ ln -s /krypton/krypton2/keyfile.dat
krypton2@melinda:/tmp/tmp.Wf2OnCpCDQ$ ls
keyfile.dat
krypton2@melinda:/tmp/tmp.Wf2OnCpCDQ$ chmod 777 .
krypton2@melinda:/tmp/tmp.Wf2OnCpCDQ$ /krypton/krypton2/encrypt /etc/issue
krypton2@melinda:/tmp/tmp.Wf2OnCpCDQ$ ls
ciphertext keyfile.dat