SubstitutionDifficulty: Medium
Keyword cipher
Every letter is swapped for another using a scrambled alphabet built from a secret word. Easy to remember, hard to guess.
Try it
27 characters
Result · Keyword cipher
Paboaq jappzca slo qda bite
How it works
- 1Pick a secret word, say ZEBRAS, and cross out any repeated letters.
- 2Write it at the start of a new alphabet and fill in the remaining letters in normal order: ZEBRASCDFGHIJKLMNOPQTUVWXY.
- 3Put this new alphabet under the normal one: A becomes Z, B becomes E, C becomes B, D becomes R, and so on.
- 4Replace each letter of your message with the one below it. Decoding goes the other way, and without the word it is hard.
Example
Hello world
Daiil vloir
Did you know
Scrambled alphabets built from a keyword are among the oldest and most widespread ciphers. Their weakness is that letters still behave the same way: E is the most common letter in English, and in Czech too. As early as the 9th century the Arab scholar al-Kindi used this to invent frequency analysis.
Try to decode
This message is encrypted with Keyword cipher using the default settings:
KEES KE TS SDE AQFNCE
Hint
The key is TAJNE (Czech for secret). The new alphabet is TAJNEBCDFGHIKLMOPQRSUVWXYZ - A becomes T, B becomes A.
Show solution
MEET ME AT THE BRIDGE
More ciphers in this category
- Caesar cipherEvery letter moves a fixed number of places along the alphabet. The most famous cipher in the world and a perfect first step.
- Vigenère cipherA Caesar cipher with a password: each letter shifts by a different amount set by the keyword. Much tougher than plain shifting.
- Polybius squareLetters in a 5x5 grid, each written as a pair of numbers: row and column. You can tap it, flash it or clap it.
- AtbashThe alphabet flipped like a mirror: A becomes Z, B becomes Y. No key, no settings, and decoding is the same as encoding.