Crib (probable word)
A crib is a guessed plaintext fragment used to test positions, keys, or structure in a ciphertext.
Definition
A crib is a word, phrase, header, or pattern suspected to occur in the plaintext. The analyst aligns it with ciphertext positions and checks whether the implied key or transformation remains consistent elsewhere.
Choosing a crib
Greetings, dates, protocol markers, file signatures, repeated formats, and topic-specific vocabulary provide candidates. A crib is not confirmed known plaintext; it becomes useful only when independent evidence supports the alignment.
Applications and limits
Cribs helped attack classical machines and reused one-time-pad keystreams. A wrong guess creates false leads, and secure modern encryption prevents local plaintext guesses from revealing corresponding key material.
No. It is probable plaintext until verified.
It slides a guessed fragment across related ciphertexts, testing where the resulting text looks plausible.
It can be tried, but context-specific and structurally constrained guesses are much stronger.