OverTheWire - Krypton - Level 1 to Level 2

Description:

Level Info:

Krypton 2

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.

Solution:

1. [Comment] Connect to server and login with username, krypton2, and password, ROTTEN.
2. sp@simple-plan:~|=> ssh krypton2@krypton.labs.overthewire.org
   ...
   krypton2@krypton.labs.overthewire.org's password: ROTTEN
3. [Comment] Change directory to the one where we can access the files for krypton levels
4. krypton2@melinda:~$ cd /krypton
5. krypton2@melinda:/krypton$ ls
   

   krypton1  krypton2  krypton3  krypton4  krypton5  krypton6

6. krypton2@melinda:/krypton$ cd krypton2
7. krypton2@melinda:/krypton/krypton2$ ls
   

   README  encrypt  keyfile.dat  krypton3

8. [Comment] Check the readme file
9. krypton2@melinda:/krypton/krypton2$ cat README
   

   Krypton 2
   
   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.
   
   

10. [Comment] Show me the details
11. krypton2@melinda:/krypton/krypton2$ ll
    

    total 15
    drwxr-xr-x 2 root     root     1024 Jun  6  2013 ./
    drwxr-xr-x 8 root     root     1024 Jun 12  2013 ../
    -rw-r----- 1 krypton2 krypton2 1060 Jun  6  2013 README
    -rwsr-x--- 1 krypton3 krypton2 8828 Jun  6  2013 encrypt*
    -rw-r----- 1 krypton3 krypton3   27 Jun  6  2013 keyfile.dat
    -rw-r----- 1 krypton2 krypton2   13 Jun  6  2013 krypton3

12. krypton2@melinda:/krypton/krypton2$ cat keyfile.dat
    

    cat: keyfile.dat: Permission denied

13. krypton2@melinda:/krypton/krypton2$ cat krypton3
    

    OMQEMDUEQMEK

14. krypton2@melinda:/krypton/krypton2$ ./encrypt
    

     usage: encrypt foo  - where foo is the file containing the plaintext

15. [Comment] Basically, we should be able to use the executable 'encrypt' to find out the key.
16. [Comment] However, there are always error messages.
17. krypton2@melinda:/krypton/krypton2$ ./encrypt /tmp/sp_krypton2/plaintext
    

    failed to create cipher file 

18. [Comment] So, let's try to bruteforce the ciphertext.
    Reference: http://www.xarg.org/tools/caesar-cipher/
    OMQEMDUEQMEK > CAESARISEASY
19. [Comment] It's done! Let's go to the next level!