Fractionated Morse Cipher

What is Fractionated Morse?

Fractionated Morse is a cipher that combines Morse code with a substitution cipher. It converts plaintext to Morse, groups the symbols into trigraphs (groups of 3), and substitutes each trigraph with a letter using a keyword-based alphabet.

How It Works

Encryption

1. Convert plaintext to Morse code
2. Use 'x' as a letter separator between Morse letters
3. Split into groups of 3 characters (trigraphs)
4. Replace each trigraph with the corresponding letter from the keyed alphabet

The Trigraphs

There are 27 possible trigraphs (3³) using dot, dash, and x. Only 26 are used, mapping to letters A-Z in the keyed alphabet.

Fractionated Morse in Geocaching

This cipher appears in puzzles because:

• Morse theme: Telegraph and radio-themed caches
• Double encoding: Combines Morse with substitution
• Keyword: Finding the keyword is part of the puzzle
• Historical: Used by hobbyists and amateur radio operators

Cryptanalysis

Attacking Fractionated Morse:

• Without keyword: Standard frequency analysis on the ciphertext
• Short messages: May not have enough data for analysis
• Known plaintext: Greatly simplifies finding the keyword
• Dictionary attack: Try common keywords