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5 articles with this tag.
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
The two-square cipher resists the ciphertext-only search that breaks Playfair and four-square, because it has no fixed reference squares. But a crib of known plaintext breaks it in seconds. Learn the known-plaintext attack, with runnable Python.
13 min read
Playfair defeated single-letter frequency analysis by encrypting pairs of letters through a 5×5 key square. But the same simulated-annealing idea that cracks the substitution cipher still works here too, once you swap in quadgram statistics and a richer set of moves.
20 min read
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
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
