Cipher catalogue
Every cipher can encode and decode. Each comes with a guide, a story and a challenge to try.
24 ciphers
- Encoding
Morse code
Letters as short and long signals - dots and dashes. Send it with sound, light or taps.
Open - Substitution
Caesar cipher
Every letter moves a fixed number of places along the alphabet. The most famous cipher in the world and a perfect first step.
Open - Transposition
Reverse text
The simplest transposition: the letters stay, you just read them backwards - the whole text, word by word, or as a pyramid.
Open - Encoding
Letter numbers (A1Z26)
Swap every letter for its place in the alphabet: A is 1, B is 2, and so on. Roman numerals work too.
Open - Substitution
Vigenère cipher
A Caesar cipher with a password: each letter shifts by a different amount set by the keyword. Much tougher than plain shifting.
Open - Substitution
Polybius square
Letters in a 5x5 grid, each written as a pair of numbers: row and column. You can tap it, flash it or clap it.
Open - Graphic
Pigpen cipher
Every letter is a piece of a grid or a cross, sometimes with a dot. Learn four shapes and you can write secret notes.
Open - Encoding
Phone keypad cipher (multi-tap)
Write like on an old button phone: press the key's number as many times as the letter's place on the key. C is 222.
Open - Substitution
Atbash
The alphabet flipped like a mirror: A becomes Z, B becomes Y. No key, no settings, and decoding is the same as encoding.
Open - Graphic
Polish cross
Each letter is a frame from a # grid with one dot. The frame picks the group, the dot picks the letter inside it.
Open - Transposition
Rail fence cipher
Write the message in a zigzag across several fence rails, then read it off rail by rail. Tidy text turns into apparent chaos.
Open - Encoding
Binary code
Text written with only zeros and ones, the way a computer sees it. Choose 8, 7 or 5 bits.
Open - Transposition
Skip cipher (every N-th letter)
Letters are stored at every N-th position, and after reaching the end you start again from the second slot. A scrambled text that hides your message.
Open - Substitution
ROT13
A Caesar cipher with a shift of 13: the same steps encode and decode. No settings, just one click.
Open - Substitution
Keyword cipher
Every letter is swapped for another using a scrambled alphabet built from a secret word. Easy to remember, hard to guess.
Open - Transposition
Grid cipher
Write the text into a square grid along diagonals, a spiral or a zigzag, then read it row by row. The letters only change places.
Open - Graphic
Chinese cipher
Vertical lines count the column and horizontal lines count the row of a 5x5 table. The lines cross like a Chinese character.
Open - Encoding
ASCII code (decimal)
Replace every character with its number in the computer table: A is 65, B is 66, a is 97.
Open - Transposition
Columnar transposition
Write the message in rows under a keyword and read it off by columns in the alphabetical order of the key letters.
Open - Encoding
Hexadecimal code (hex)
Every character becomes a pair of digits 0-9 and letters A-F. A compact notation programmers love.
Open - Graphic
Flag semaphore
Two flags, eight arm positions. Each pair of positions is one letter - the signaller shows it, you read it.
Open - Graphic
Braille
Six dots in a 2x3 cell, one pattern per letter. A writing system read by fingertips - which you can also draw in colours.
Open - Graphic
Bitmap cipher
Letters as pictures made of squares - hidden as a barcode, an inverse, colours or compressed numbers.
Open - Graphic
Vector cipher
Letters drawn from lines in a 3x3 dot grid - rotated, inverted, or two letters stacked in colour.
Open