Morbit cipher

The Morbit cipher is the paired variant of the Pollux cipher. The idea is elegant: rather than substituting each Morse symbol individually (., -, /), group the symbols in pairs and assign a unique digit to each of the nine possible pairs.

Principle

Three Morse symbols (., -, /) grouped by pairs yield exactly 3² = 9 pairs:

.. .- ./ -. -- -/ /. /- //

Each pair maps to a digit 1–9 by a secret permutation:

Morse pair	Digit
..	5
.-	2
./	1
-.	7
--	4
-/	9
/.	6
/-	3
//	8

The key is that permutation — 9! = 362,880 possible keys, far beyond human brute force but trivial for a computer (under a second).

Example

The cleartext CIPHER encodes to Morse:

C → -.-./
I → ../
P → .--./
H → ..../
E → ./
R → .-./

Concatenated: -.-./../.--./...././.-./ — 24 symbols. Group by 2: -. -. /. ./ .- -. /. .. ./ ../ .. ./ .-. / — each pair becomes a digit per the table. A 6-letter cleartext yields a 12-digit ciphertext (half the length of Pollux).

Strengths and weaknesses

Strengths

• Half the ciphertext length of Pollux for the same input, thanks to pair grouping.
• 9 frequency classes instead of 3 — pair-frequency analysis is more delicate than Pollux’s.
• Keyspace of 9! — about 200× more than a 6-letter alphabet.

Weaknesses

• Non-uniform distribution — pairs .., .-, /. are structurally more common in Morse, and their digit images inherit that bias. Frequency analysis on 1000+ pairs reveals the permutation.
• Imperfect independence — the end of every Morse letter is always /, which constrains the position of digits encoding */ or /.. That regularity is an attack channel.
• No randomness — unlike Pollux, where multiple digits exist per symbol, here the permutation is bijective: the same cleartext always produces the same ciphertext. No protection against known-plaintext attacks.

Variants

• Pollux — single-symbol variant. See the dedicated page.
• Extended Morbit — adds Morse pairs + position-in-word, breaking the / regularity.
• Morbit + textual key — the permutation is derived from a keyword instead of being arbitrary, shrinking the keyspace but easing memorisation.

How to attack it by hand

1. Count digit frequencies. On a long enough text, the three digits encoding .., .-, /. (the most frequent Morse pairs) emerge.
2. Align those frequencies with a theoretical Morse distribution to identify the nine pairs.
3. Rebuild the full Morse.
4. Decode to the standard alphabet.

For 200+ digit messages, manual attack succeeds in 30 minutes to an hour.

In CipherChronicle

Morbit illustrates the effect of grouping: lifting the number of frequency classes (from 3 to 9) raises attack difficulty and adds an intermediate rung between Pollux and true polyalphabetic ciphers. Morbit puzzles will keep the public “9 pairs → 9 digits” table but hide the permutation — that’s where the difficulty lives.