Mandatory settings

Input: Acceptable characters for input are: A-Z, a-z, 0-9, space (" "), and period ("."). Spaces are treated as underscores when encrypting. If you include other characters you must sanitize the input or the encryption process will fail.

Sanitize: Sanitizing the text remove all other characters, symbols, and punctuation. Exclamation marks ("!") and question marks ("?") will be converted to periods. Only sanitize the text when encrypting.

Character count: The number will turn blue when the input length evenly matches the selected group size(s). If the lengths do not match then random characters will be padded to the end of the input when encrypting. This is irrelevant when decrypting.

The keyed alphabet takes your key, removes duplicates, and appends all remaining characters (A-Z, a-z, 0-9, underscore, and period) to the end. A longer key creates a more unique alphabet. This 64-character alphabet is used to fill the cipher table below.

The cipher table arranges the keyed alphabet onto an extended (8x8) Polybius square which is used to encrypt or decrypt the message.

Input characters are identified by their location along three pairs of rows and columns (identified by 0 and 1). The location data is mixed together and new output characters are derived. This method combines transposition and fractionation to achieve diffusion.

You can click a letter in the table to see the location data for that letter.

Named Osm after the Czech word for "eight" - the central component of this cipher is an 8x8 Polybius square. This cipher was inspired by Felix Delastelle's bifid cipher. Like bifid, it was designed to be possible entirely with pen and paper, aside from a few additions such as the stream and hash features.

This cipher is untested and was created for fun. If you require strong encryption use a modern cryptographic solution.