= Affine =

Affine cipher is a type of [[substitution]] cipher.

The cipher is of model

f(x) = ax + b mod 26

Where x is some number corresponding to a letter, 0-25. a and b are variables.

To decipher, the formula is of form

f(y) = a^-1(y - b) mod 26

Where y is the ciphertext value, and a^-1 is the modular multiplicative inverse
of a