Gardening (cryptanalysis)

In cryptanalysis, gardening was a term used at Bletchley Park, England, during World War II for schemes to entice the Germans to include known plaintext, which the British called "cribs," in their encrypted messages. This term presumably came from RAF minelaying missions, or “gardening” sorties, so called because sectors of the coastal waters around Europe were given code-names based on fruits and vegetables. The technique is claimed to have been most effective against messages produced by the German Navy's Enigma machines.

A well-known example involved mines. If the Germans had recently swept a particular area for mines, and Bletchley Park was in need of some cribs, they might (and apparently did on several occasions) direct that the area be mined again. This would hopefully evoke encrypted messages from the local command mentioning 'Minen' ('mines' in German) and/or the location, and perhaps messages also from the headquarters with minesweeping ships to assign to that location, mentioning the same. It worked often enough to try several times. In modern terms, this was a chosen plaintext attack, because plain text effectively chosen by the British was injected into the ciphertext.