Important Notice
The encryption and encoding tools on this page are provided solely for fun, learning, and general educational exploration. They are not intended for use on amateur radio, and must not be used to obscure the meaning of any transmission.
Amateur radio regulations in many countries — including the UK and US — prohibit the use of encryption or any method designed to make a message unintelligible to other radio users. These tools are therefore offered for curiosity, experimentation, and personal study only, not for on‑air communication.
Use the links below to jump forward to puzzles
QWERTY Keyboard Substitution
How it works
This cipher replaces each letter using the physical order of the QWERTY keyboard rather than the normal alphabet. The keyboard row is treated as the substitution sequence, so each ciphertext letter corresponds to a different plaintext letter based on its position.
For example, in this system:
Because the mapping is fixed and consistent, every time the same ciphertext letter appears it represents the same real letter.
To solve the puzzle, study the encrypted word, look for familiar word shapes, and use frequency and pattern recognition to work backwards to the keyboard mapping.
In short:
👉 Based on QWERTY keyboard order
👉 Each letter always maps to the same partner
👉 Pattern spotting reveals the solution
Letter Substitution
This puzzle uses a fixed letter-for-letter substitution cipher. Each letter of the normal alphabet is replaced with a different letter according to a secret mapping. The same plaintext letter always encrypts to the same ciphertext letter.
To solve the puzzle, look for patterns in the encrypted word and use the provided cribs (known plaintext examples) to reconstruct the substitution alphabet. Once you have identified enough letter pairs, the remaining letters usually fall into place quickly.
In short:
👉 One letter always equals one other letter
👉 Cribs help you reverse-engineer the alphabet
👉 Pattern spotting is the key skill
Caesar Cipher
The Caesar cipher shifts every letter of the alphabet forward by a fixed number of positions. For example, with a shift of 3, A becomes D, B becomes E, and so on, wrapping around at Z.
All letters move by the same amount, so once you discover the shift value, the entire message can be decoded immediately.
To break it, try mentally shifting the text backwards or look for common word shapes and short words.
In short:
Every letter is moved forward by the same number The shift is constant across the whole message Find the shift → solve the puzzle
Rail Fence Cipher
How it works
The Rail Fence cipher is a transposition cipher — it doesn’t replace letters, it rearranges them. The message is written in a zig-zag pattern across a set number of “rails” (rows). Once written, the ciphertext is created by reading the rails row by row from top to bottom.
For example, with 3 rails the text moves:
down through the rails,
then back up,
repeating this zig-zag until the message is complete.
To decode, you reconstruct the same zig-zag pattern and reassemble the message by reading along the zig-zag route.
In short:
👉 Letters stay the same, but their order changes
👉 Written in a zig-zag across rails
👉 Read off row-by-row to form the ciphertext
Use the Try your own tool to choose the rail count and encode/decode your own messages — and the Diagram view shows exactly how the zig-zag layout works.
Letter Substitution #2
How it works
This cipher builds a scrambled alphabet using a secret keyword. The keyword is written first (with duplicate letters removed), and the remaining unused letters of the alphabet are added afterwards.
The normal alphabet is then mapped against this keyed alphabet to perform the encryption.
Because the alphabet is mixed rather than shifted, this cipher is stronger than a Caesar shift. Use the provided crib (known plaintext fragment) and word patterns to begin reconstructing the substitution.
In short:
👉 Alphabet is rearranged using a keyword
👉 Each letter still maps consistently
👉 Use the crib and word shapes to break it
Playfair Cipher
How it works
The Playfair cipher encrypts text in pairs of letters (digraphs) rather than single characters. A 5×5 letter grid is first constructed using a secret keyword, with the remaining letters of the alphabet filling the unused spaces. In this system the letters I and J share the same square.
To encrypt:
The message is split into letter pairs
If a pair contains the same letter twice, an X is inserted between them
If the message has an odd length, an X is added to the end
Each pair is then transformed using the Playfair grid rules
Because it works on pairs instead of individual letters, Playfair is significantly stronger than simple substitution ciphers.
In short:
👉 Text is encrypted two letters at a time
👉 A keyword builds the 5×5 grid
👉 I and J are combined
👉 X may appear as a filler letter
Use the Try your own tool to experiment with different keywords and see how the digraph encryption behaves.
Columnar Transposition
How it works
Columnar transposition is a rearrangement cipher. The letters of the message do not change, but their order is scrambled using a secret keyword.
First, the plaintext is written into rows under the keyword. The letters of the keyword are then alphabetised, and the columns are read in that new order to produce the ciphertext.
In these puzzles, the keyword is not given — part of the challenge is to work out the correct column structure from the ciphertext and the provided hints.
How to approach it
When the keyword is unknown, analysts typically:
Look for likely word breaks
Try different column counts
Search for recognisable fragments
Use the clue to guide the reconstruction
Because no letters are substituted, solving the correct column layout will immediately reveal readable text.
In short:
👉 Letters stay the same — only their positions change
👉 A hidden keyword controls the column order
👉 You must reconstruct the grid to read the message
Use Try your own to experiment with keywords and see exactly how the columnar rearrangement works.
Morse Challenge Mode
How it works
This puzzle uses Morse code — a signals alphabet made from dots (·) and dashes (–). Your job is to decode the transmission and type the plain text message.
On this page:
Letters are separated by spaces
Words are separated by a / (slash)
Challenge rules
A timer starts as soon as a new transmission loads.
You have 3 strikes — each wrong answer adds a strike.
On the third strike, the solution is automatically revealed.
Your best time is saved on your device (so you can try to beat it).
Audio mode
Use Play to hear the transmission as beeps. You can adjust:
WPM (speed)
Tone (pitch)
Use Try your own to encode text into Morse or decode your own Morse strings back into plain text.
Variable Shift Cipher
How it works
This cipher looks like a standard Caesar shift — but with a twist.
Instead of using one fixed shift, each word is shifted by its own length.
That means:
Count the number of letters in the word
Shift every letter in that word forward by that number
Wrap around the alphabet as usual (after Z comes A)
Examples
BUNKER → 6 letters → shift +6 → HATQKX
RADIO → 5 letters → shift +5
PINEAPPLE → 9 letters → shift +9
Each word in the message is treated separately, so multi-word messages will use different shifts within the same line.
In short:
👉 Each word uses its own Caesar shift
👉 Shift amount = word length
👉 Letters wrap around A–Z
👉 Spaces and punctuation stay the same
Use Try your own to experiment and see how the shifting changes with different word lengths.