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#Four-Square Cipher

3 articles with this tag.

A visual representation of the four-square cipher breaker recovering two key squares
Basic Classic Symmetric Breakers Advanced

Breaking the Four-Square Cipher with Two Key Squares

The four-square cipher hides letter frequencies behind two keyed grids, but it is still a pencil-and-paper cipher. Learn how simulated annealing with quadgram statistics recovers both secret squares from the ciphertext alone, with runnable Python.

14 min read

A visual representation of the Four-Square Cipher
Basic Classic Symmetric Intermediate

The Four-Square Cipher

Learn about the four-square cipher, a digraph substitution cipher that uses four 5x5 grids to encrypt letter pairs without Playfair's awkward same-row and same-column special cases.

12 min read

A visual representation of the Two-Square Cipher
Basic Classic Symmetric Intermediate

The Two-Square Cipher

Learn about the two-square cipher, a digraph substitution cipher that sits between Playfair's single grid and four-square's four grids: two independently keyed squares, one uniform encryption rule.

13 min read

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