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3 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
A monoalphabetic substitution key is one arbitrary permutation of 26 letters: 26! of them, far too many to brute force and immune to Kasiski or the Index of Coincidence since there's no repeating key. Here's how frequency analysis and a hill-climbing search crack it anyway.
26 min read
