Cabinet Noir
>Cryptoanalysis / Autokey cipher
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Vigenère's actual cipher: the key starts with a short primer, then the plaintext itself feeds the keystream.
Type
polyalphabetic substitution cipher
Breaking it
hard to break by hand
Era
Renaissance — the real 1586 Vigenère
Name
Giovan Battista Bellaso, 1553
Modes
encrypt · decrypt · cryptoanalysis
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Tool
Cryptoanalysis
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History
Practice
Ciphertext to break
Hints
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Custom
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Show English-likeness score of each implied fragment
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Mark the most English-like offset
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Live plaintext preview
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1. Guess a word
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2. Drag it along
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3. Unroll the key
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4. Done
Guess a probable word
In autokey the key is the plaintext itself: one guessed word unravels the whole message. Pick a word that likely appears in the text.
THE
AND
Primer length
how long the secret primer was (2-12)
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Created by Denys Grybov in 2021
v.0.4.0 // released on 27.10.2026