frequencyanalysis.md

Frequency Analysis with Caesar Cipher

Remember the Caesar Cipher challenge?

The Caesar Cipher, also known as a shift cipher, is one of the oldest and simplest forms of encrypting a message. It is a type of substitution cipher where each letter in the original message (which in cryptography is called the plaintext) is replaced with a letter corresponding to a certain number of letters shifted up or down in the alphabet.

So for example, if our letter is A and our shift is 4, we get E.

Get the key:

With a given encrypted text, we can get the key by analyzing the letters frequency. For example, in English E is the most used letter.

Example

If you have pixxiv, we see that there are 2 i and 2 x. We'll start with i, and we'll suppose that it's an e.

i - e = 4 // We aren't substracting letters but their position in the alphabet

Let's try to decode pixxiv with 4.

And we get letter, which is an English word, so the key was 4.

What you need to do?

Try to get the key of the following phrase:

aol xbpjr iyvdu mve qbtwz vcly aol shgf kvn