Pollux cipher

The Pollux cipher is a clever twist on Morse code popularised in amateur cryptographic circles in the mid-20th century. Morse on its own is a public code: trivially decodable by anyone with the international table. Pollux adds a layer of homophonic substitution: each Morse symbol (dot, dash, separator) is replaced by several different digits spread across 0-9.

Principle

Pollux operates in two steps:

1. Convert to Morse: each cleartext letter becomes a sequence of dots (.), dashes (-) and separators (/ between letters, // between words).
2. Homophonic substitution: build a table assigning each digit 0-9 to one of the three Morse symbols:
   • 3 or 4 digits for dots,
   • 3 or 4 digits for dashes,
   • 2 or 3 digits for separators.

When enciphering, walk through the Morse stream symbol by symbol and pick a digit at random among those allowed for that symbol. The ciphertext is therefore a digit stream where the same Morse sequence can yield different ciphertexts — the homophonic property.

Example

Sample table:

. → 3, 8, 2
- → 9, 4, 1
/ → 7, 5, 0, 6

The cleartext CIPHER encodes to Morse -.-./../.--./...././.-./ (with / between letters).

One possible encoding: 9, 3, 9, 8, 7, 2, 8, 7, 8, 9, 4, 8, 7, 3, 8, 2, 8, 7, 8, 7, 9, 2, 4, 7 — but another run with the same table would yield a different stream.

Strengths and weaknesses

Strengths

• Statistical flattening — digits 0-9 surface at near-uniform frequency, hiding Morse’s classic 90%-dots-and-dashes signature.
• Variability — encrypting the same message twice produces two different ciphertexts, defeating known-plaintext attacks.
• Trivial to apply by hand with a simple table.

Weaknesses

• Morse remains structural — only three families of symbols exist. A paired-frequency analysis (count 33, 38, 82 against 94, 41) separates dots from dashes from separators quickly.
• Imperfect uniformity — if the table assigns 3 digits to dots and 3 to dashes, those classes balance out — but separators (rare in Morse) are under-represented. Frequency counting reveals the separator class within a few lines.
• No variable secret key — the table is fixed for the whole message.

Variants

• Morbit — pair-of-Morse-symbols variant. See the dedicated page.
• Extended Pollux — uses base-16 or base-32 instead of 0-9 to absorb more redundancy.
• Pollux + transposition — apply a transposition to the digit stream to break the groupings.

How to attack it by hand

1. Count the frequency of each digit. A natural three-class partition (dots, dashes, separators) should appear.
2. Hypothesis: the most frequent classes are dots and dashes; the rarest, separators.
3. Rebuild the Morse stream by replacing each digit with its candidate class.
4. Decode the standard Morse.

For messages of 50+ digits, the frequency partition resolves in minutes.

In CipherChronicle

Pollux is a homophony tutorial: it shows how to add redundancy in the table to flatten outgoing frequencies. Pollux puzzles bridge raw Morse practice and classical homophonic substitution (multi-symbol substitution).