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…
Cipher Hub
Classical cipher challenges with a Workbench for analysis, transformation, and hypothesis testing.
Featured Cipher Challenges
S.D.L.'s First Challenge
A correspondent signing as S.D.L. submitted this three-paragraph cryptogram from Stonington, Connecticut, and Edgar Allan Poe printed it in the July 1841 issue of *Graham's Magazin…
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.
My first Columnar transposition
This is a columnar transposition: the characters are unchanged, but whole vertical slices have been rearranged. Ignore the displayed groups of five. Make a structural guess by test…