What is the Affine cipher?

The Affine cipher turns each letter into a number from 0 to 25, multiplies it by one key number, adds another, and turns the result back into a letter. The multiplier has to share no factors with 26, so there are only 12 choices for it and 26 for the shift. That makes 312 keys in all, few enough to try every one.

With "Try all" on, CacheCrack decodes with every key and shows the results that look most like English. A Caesar cipher is an Affine cipher with a multiplier of 1, and Atbash is one with a multiplier of 25 and a shift of 25.

Example

IHHWVCSWFRCP with a = 5 and b = 8 decodes to AFFINECIPHER.