Fractionated Morse Cipher
Follow the entire path from plaintext to Morse, separators, trigrams, keyed letters, and back again.
What is the Fractionated Morse Cipher?
Fractionated Morse first converts plaintext letters to Morse. It inserts separators, concatenates the symbols, splits the stream into groups of three, and maps each trigram to a letter in a keyed alphabet.
The name “fractionated” comes from breaking and regrouping the Morse representation rather than encrypting the original letters directly.
The cipher mechanics on this page are self-contained. Science Olympiad event formats, allowed variants, and tournament constraints can change by season; the current official Rules Manual and official clarifications take precedence.
No outside reference is assumed. Work through Foundations → Complete Reference → Encryption → Decryption in order, then use the competition and cryptanalysis sections.
What you need to know
- Dots and dashes represent Morse code.
- The Daily Cipher engine uses x as a separator: one x between letters and two x between words before regrouping.
- There are 26 usable trigrams from {., -, x} when xxx is excluded—exactly enough to map to A–Z.
Beginner glossary
| Term | Meaning |
|---|---|
| Morse stream | The dots, dashes, and separator x symbols produced before fractionation. |
| Separator x | One x separates Morse letters; two x symbols separate words in this site’s convention. |
| Trigram | A group of exactly three symbols from {., -, x}. |
| Keyed alphabet | Keyword with duplicate letters removed, followed by unused alphabet letters. |
| Crib | Known plaintext fragment used to constrain trigram/key mappings during cryptanalysis. |
Keep this beside you while solving
International Morse letters
| Letter | Morse |
|---|---|
| A | .- |
| B | -... |
| C | -.-. |
| D | -.. |
| E | . |
| F | ..-. |
| G | --. |
| H | .... |
| I | .. |
| J | .--- |
| K | -.- |
| L | .-.. |
| M | -- |
| N | -. |
| O | --- |
| P | .--. |
| Q | --.- |
| R | .-. |
| S | ... |
| T | - |
| U | ..- |
| V | ...- |
| W | .-- |
| X | -..- |
| Y | -.-- |
| Z | --.. |
Trigram order used by The Daily Cipher
| Index | Trig. | Index | Trig. |
|---|---|---|---|
| 1 | ... | 14 | --- |
| 2 | ..- | 15 | --x |
| 3 | ..x | 16 | -x. |
| 4 | .-. | 17 | -x- |
| 5 | .-- | 18 | -xx |
| 6 | .-x | 19 | x.. |
| 7 | .x. | 20 | x.- |
| 8 | .x- | 21 | x.x |
| 9 | .xx | 22 | x-. |
| 10 | -.. | 23 | x-- |
| 11 | -.- | 24 | x-x |
| 12 | -.x | 25 | xx. |
| 13 | --. | 26 | xx- |
The keyed cipher alphabet is placed against these trigrams in order.
Order matters
Build the entire Morse stream first, including separators, then split it into groups of three. Do not group each Morse letter independently.
x
until the last trigram is complete. During decoding, trailing separator padding should not be mistaken for a new plaintext letter.
How encryption works
Convert plaintext to Morse
Write each letter as dots/dashes.
Insert separators
Use x between letters and xx between words.
Regroup into threes
Ignore original Morse letter boundaries after building the stream.
Map each trigram
Find the trigram index and output the corresponding letter from the keyed alphabet.
How decryption works
Convert ciphertext letters to trigrams
Use the keyed alphabet to find each ciphertext letter’s trigram.
Concatenate the trigrams
Rebuild one long stream of ., -, and x.
Recover separators
x marks letter boundaries and xx marks word boundaries.
Decode Morse
Translate each Morse sequence back to plaintext letters.
How to approach it in Codebusters practice
- A crib can give a powerful alignment clue in cryptanalysis modes.
- Do not confuse x separators with Morse dashes.
- Build the keyed alphabet carefully: remove repeated keyword letters, then append unused alphabet letters.
What the problem gives you vs. what you produce
| Part | What to expect |
|---|---|
| You may be given | Ciphertext plus a keyword/key, or a cryptanalysis problem with a crib. |
| You must find | The plaintext by reversing keyed letters → trigrams → Morse stream → Morse letters. |
| Fastest first move | Write the keyed alphabet and the 26-trigram order side by side before decoding. |
How to attack an unknown or partially known key
- Known plaintext lets you build the corresponding Morse stream and compare trigram alignments with ciphertext letters.
- Repeated ciphertext letters indicate repeated trigrams, not necessarily repeated plaintext letters.
- A crib can constrain both alignment and keyed-alphabet mappings.
Follow one example from start to finish
CIPHER
SOS
...x---x...
... x-- -x. ..x
CWNP
Before moving on, make sure you can answer these without another site:
- Can you translate one plaintext word to Morse with x separators?
- Can you explain why xxx is excluded from the 26 trigram list?
- Can you reverse one ciphertext letter to its trigram using the keyed alphabet?
Common mistakes
Using spaces instead of x inside the Morse stream.
Regrouping before inserting the letter/word separators.
Including xxx as a normal trigram.
Building the keyed alphabet with duplicated keyword letters.
Competition speed strategies
Keep the full Morse table and trigram order visible.
Write the stream in one uninterrupted line before drawing trigram separators.
In decryption, reconstruct the x separators before attempting any Morse-letter lookup.
What to remember under time pressure
See every transformation
Use the lab to change inputs and keys, keep the relevant reference material visible, inspect each intermediate transformation, and then read the “How to reverse it” panel so encryption and decryption connect.