A Beginner's Guide to Cipher Solving

written by Vivian Murphy

Solving Ciphers: Caesar, Polybius, and Vigenere

The last cipher I will be teaching you is one that, similarly to the Polybius square, is notoriously difficult to crack without its key. It is the Vigenere cipher, invented in the 16th century and not broken until almost 200 years later, and its workings are simple enough that they will surprise you. The easiest way to explain it is in relation to the previously described Caesar cipher, as it shifts the letters of the plaintext forward to become ciphertext. However, unlike the Caesar cipher, it uses a key phrase similar to your last puzzle. It then cycles through the key phrase and takes the numerical position of the letter in the alphabet starting from zero and moves it forward that many positions, repeating the key phrase when it runs out. So, for example, if we are trying to encrypt the plaintext 'Lightning' using key phrase 'Rain,' we shift R forward 11 places, as L is the 12th letter in the alphabet, then we do not shift I forward, as A is the 1st letter in the alphabet and we count from 0, and continue onward, until we have 'Ciouknqax' as our ciphertext.

when it comes to decrypting the viGenere cipher, you will absolutely need the key to decRypt it propErly. the eAsiest way is To try and find some hint that works as the key, but alternatively you can try to find the length of the key by trying to find where it repeats.

So, like last time, Ive hidden a small little key for you--which should be pretty easy to find. Use the key phrase that it forms in order to solve it, for which a Vigenère square may be useful for you.