Bifid is a cipher which combines the Polybius square with transposition, and uses fractionation to achieve diffusion. Keys for the Bifid cipher consist of a 25 letter 'key square'. The keysquare can be generated using a keyword and the rest of the spots will be filled with the remaining letters of the alphabet in order. You may also randomly generate the keysquare if you wish. Note that usually the letter 'j' is merged with 'i' (but you can customize that below to your liking in the Alphabet Options).

You can choose a period grouping to further group the blocks into a certain size (which forms part of the key) or leave blank to have it set to the length of the text.