So, the Caesar Cipher is nice but there are only 26 possible keys. Using just brute force a computer could decrypt a Caesar Cipher within milliseconds. We can increase the number of possible keys to make a ciphertext harder to decrypt. Our cipher alphabet in the Caesar Cipher just consisted of the letters of the alphabet shifted, but what if we did not just shift the letters but completely randomized the order of the letters in the cipher alphabet:

Ptext: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Ctext: NIZJSMTWPKFUDRAVHGXBCOEYLQ

This vastly increases the number of keys thereby making the cipher harder to decrypt.

Encryption:

Ptext: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Ctext: NIZJSMTWPKFUDRAVHGXBCOEYLQ

To encrypt the message: "I LIKE GOOGLE CHROME" we would find "I" in the plaintext alphabet and find the letter directly under it. In this case the letter is "P". So "I" would encrypt to "P". "L" would encrypt to "U", and so on until we have:

I LIKE GOOGLE CHROME
P UPFS TAATUS ZWGADS

Decryption:

Ctext: NIZJSMTWPKFUDRAVHGXBCOEYLQ
Ptext: ABCDEFGHIJKLMNOPQRSTUVWXYZ

To make decryption easier we can alphabetize the ciphertext alphabet:

Ctext: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Ptext: OTUMWKRQBDJYFAVIZNEGLPHSXC

We do the same thing for encrypting as decrypting. Find the letter of the Ciphertext in the cipher alphabet and find the letter under it.

P UPFS TAATUS ZWGADS
I LIKE GOOGLE CHROME