Crib
In cryptanalysis, crib was the term used at Bletchley Park for known plaintext which could be used in the cryptanalysis of German and other messages. The term entered cryptography from this usage.Bletchley Park cryptographers obviously had something of a sense of humor, for their usage was adapted ('cribbed' even) from the student term (both verb and noun) meaning a bit of a cheat. Thus, 'I cribbed my answer from your test paper', or 'That copy of Foo's old Greek grammar has answered exercises in each chapter that Master Smythe has been using in his tests. We can use it as a crib'. The application to cryptanalysis of German messages is clear.
Examples include stereotyped salutations, endings, titles, routing codes, etc. In the case of WWII German traffic, one site, well beloved by BP, was quite bored. It reported this to headquarters each morning using precisely the same phrase, albeit encyphered using the current Engima key.
In an effort to grow a crib now and then, Bletchley Park sometimes arranged to have some gardening done.
See also: gardening, cryptanalysis
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