The Affine cipher is a monoalphabetic substitution cipher and it can be the exact same as a standard Caesarian shift when "a" is 1. Mathematically, it is represented as e(x) = (ax + b) mod m. Decryption is a slightly different formula, d(x) = a^-1(x - b) mod m.

To encode something, you need to pick the "a" and it must be coprime with the length of the alphabet. To make this easier, I have the (+) and (-) buttons to change the A to the next higher or lower coprime number.

This is your encoded or decoded text: