How Does the Affine Cipher Work

By Arthur Finegan

Who doesn't like the thrill of cracking a code or solving a puzzle? Affinecionados presents regular messages (either words or phrases) for people to decode. It's a fun way that both children or adults can build confidence with their math skills (and possibly improve their vocabulary). This book discusses how the Caesar cipher and the Affine ciphers work.

• Language: English
• Publisher: Affinecionados
• Release date: Jan 20, 2022
• ISBN: 9798201952167

Arthur Finegan

We provide you with regular messages to decode based on the Affine Cipher. Can you solve the mystery in the message?

Book preview

The Caesar Cipher

The Caesar cipher is a code where each letter is replaced with the letter that is a chosen number of letters later in the alphabet.

Here we will encode ‘this is the caesar cipher’ by replacing each letter with the letter 10 places later in the alphabet.

The first letter of this message is ‘t’. We need to find the letter 10 places later in the alphabet. The next letter is ‘u’, then ‘v’, then ‘w’, then ‘x’, then ‘y’, then ‘z’. So far, we have gone six places and we have reached the end of the alphabet. We then wrap around to the beginning of the alphabet, so next would be ‘a’, then ‘b’, then ‘c’, and then ‘d’. So, if we use a Caesar cipher with a shift of 10, then ‘t’ is encoded to ‘d’.

An easy way to code something in Caesar cipher is to first replace each letter with the number that represents its position in the alphabet.

t-h-i-s/i-s/t-h-e/c-a-e-s-a-r/c-i-p-h-e-r

becomes

20-8-9-19/9-19/20-8-5/3-1-5-19-1-18/3-9-16-8-5-18

Then increase each number by 10 to obtain

30-18-19-29/19-29/30-18-15/13-11-15-29-11-28/13-19-26-18-15-28

At this point, we notice that some of the numbers have exceeded 26, the number of letters in the alphabet. From these numbers, we will subtract 26, so that all of them will be between 1 and 26 and therefore correspond