Morbit cipher

The Morbit cipher is a classical fractionated Morse scheme used in cryptogram clubs, Science Olympiad Codebusters, and geocaching puzzles. You first write the plaintext in International Morse code, separate letters with a slash and words with a double slash, then read the stream two symbols at a time. Each of the nine possible digrams of dots, dashes, and separators is replaced by a unique digit from one through nine according to a secret key. The result is a compact string of digits that looks nothing like Morse yet still carries the full message once the same key is applied in reverse. This capability accepts either a nine-digit permutation of one through nine or a nine-letter keyword whose alphabetical ranks build that permutation, then encrypts or decrypts deterministically in a pure parse worker with no network and no randomness.

How Morbit pairs Morse symbols into digits

Morbit sits between plain Morse and heavier fractionated systems such as Fractionated Morse. After the plaintext is converted to Morse, every letter is followed by a single slash separator and every word boundary becomes a double slash. The continuous stream therefore contains only three symbols: the dit written as a period, the dah written as a hyphen, and the separator slash.

Grouping those symbols two at a time yields exactly nine digrams: two dits, dit-dah, dit-slash, dah-dit, two dahs, dah-slash, slash-dit, slash-dah, and two slashes. The secret key is a permutation that assigns each digram a unique digit from one to nine. Encryption replaces every digram with its digit; decryption expands every digit back to its digram, then Morse-decodes the recovered stream.

If the Morse stream has odd length, a final pad slash is appended so pairing never leaves a singleton symbol. That pad is harmless on decrypt because empty letter tokens are ignored. Either form is accepted here so puzzle sheets that print keywords and tooling that stores digit tables both work without a separate conversion step.

Input contract, modes, and error behaviour

On encrypt, Latin letters A through Z and digits zero through nine are Morse-coded case-insensitively; runs of whitespace become word separators; other punctuation is skipped so pasted slogans still work. On decrypt, only digits one through nine are allowed after spaces are stripped—digit zero never appears in classical Morbit and is rejected. The key must be either exactly nine characters that are a permutation of digits one through nine with no repeats and no zero, or exactly nine Latin letters whose ranks become that permutation.

Decrypt that expands to unknown Morse tokens under the supplied key also fails rather than returning garbage letters. Successful responses echo mode, the normalised numeric key, optional keyword when a letter key was used, the result string, lengths, letter and word counts, the intermediate Morse stream for teaching, the fixed digram list, and a short formula string.

Example: text MORE BITS with key five six eight nine three one seven two four (or keyword MORSECODE) encrypts to the digit string three two three seven nine seven four nine five seven eight one five eight, and decrypting that ciphertext with the same key recovers MORE BITS.

Where the Morbit cipher comes in handy

Classroom Codebusters coaches and cryptogram editors need a deterministic Morbit oracle that never invents a tenth digram and never silently accepts a zero in the ciphertext. Puzzle generators for geocaches and escape rooms want to mint digit ciphertext from a known keyword and verify that reverse decoding restores the same phrase before packaging a cache page. Failed validation does not consume balance.

Keep requests under the character limit, store the numeric key form in tests even when users type keywords, and you get reproducible Morbit encrypt and decrypt for teaching, LMS plugins, and edge workers without maintaining your own Morse tables.