The aristocrat
An Aristocrat is a monoalphabetic simple-substitution cipher that preserves word divisions and punctuation. The name comes from the American Cryptogram Association, founded in 1930…
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Featured Cipher Challenges
A Matter of Pairs
Playfair cipher. Standard Playfair transforms fixed pairs of letters rather than single letters. It uses a 5 × 5 square containing the alphabet with I and J sharing one position. R…
The Indecipherable Cipher
Vigenère cipher.
The Night Garden
This Challenge explores nocturnal pollinators, the plants that attract them, and the practical choices involved in creating a garden that supports them.
Secrets Before Paper
Adapted from Wikipedia's “History of cryptography” under CC BY-SA 4.0; changes were made.
The Rise of the Codebreakers
Adapted from Wikipedia's “History of cryptography” under CC BY-SA 4.0; changes were made.