Cryptoquest

Posted by Mariia Mykhailova on July 9, 2012

As a child I was fascinated by detective or adventure stories in which people had to break ciphers and extract hidden messages from the most innocent-looking text or images. A decade later, a beautiful cipher and the crooked path to its decoding still make my heart pant. This was one of the reasons why I took Stanford online class "Introduction to Cryptography". The very first programming assignment (breaking a one-time pad used more than once) inspired me to create a small quest featuring several historically important ciphers - the ones which don't get used in real life any more but which are so much fun to break by hand.

Here is the actual quest. It is a so-called zip-quest, the principle is: on each level you are given a ciphertext, you have to break it, figure out the message encrypted, get a password from it and apply it to unzip the archive which contains the next level. Zero-level archive (cryptoquest.zip) has no password. In all cases the plain text message contains not only the password itself but also some English text - otherwise the cryptanalysis would be too complicated, if not impossible.

Enjoy breaking the ciphers!