The 1944 Bletchley Park Cryptographic Dictionary

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ANAGRAM. v :

1. To rearrange the letters of a transposition cipher (usually by trial and error) so as to restore the original plain language.

2. (misused for). To decipher any part of a Playfair cipher, either by utilizing bigram frequencies and a knowledge of the probable plain text, or by using a previously reconstructed Playfair square or squares.

3. (misused for). To break any part of a letter-subtractor, esp. machine-cipher, depth of two or more messages by differencing and stencil-search or virtual stencil-search.

ANAGRAM KEY :

The natural numbers (i.e. from 1 upwards) of the letters of a transposition cipher rearranged into the order which these letters have in the clear text, thus showing how the cipher letters are anagramed to restore the original plain language. cf. encipher key.

ANALYSIS :

1. Systematic examination of cipher messages with a view to discovering e.g. indicators, limitations, or other characteristics of the system employed which may provide a point of attack or suggest a method of solution.

2. Systematic examination of a portion of key, esp. of a machine cipher, aimed at resolving it into its basic components.

3. (in Met.). A message containing a general description of the weather situation over a large area, e.g. Western Europe, at a particular time.

ANTI-CRIB, a :

(applied to regulations or methods). Designed to avoid giving cryptographic cribs.

APERIODIC :

(esp. of machine ciphers and keys). Showing no evidence of periodic repetition within the length of one message (owing usually to great length of key period).

ARBITRARY :

(of code-groups, indicators, etc.). Having had a provisional subtractor taken off; reduced to provisional, not true, figures or letters. cf. base

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