The 1944 Bletchley Park Cryptographic Dictionary

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BASIC BOOK :

The code-book underlying a cipher, the code-groups of which have been disguised by recipherment.

BASIC WHEEL ORDER :

(in Enigma). The wheel order prescribed in the month's keys for a particular day before the changes introduced by a Stichwort are made to it.

BEAUFORT :

Involving subtraction, not addition, in the process of enciphering or reciphering.

BEAUFORT SUBTRACTOR :

A subtractor which is applied to an encoded message by subtraction, not addition; (see the next).

BEAUFORT SYSTEM :

1. (codes). A system of reciphering code-groups with a subtractor or key in which, to produce the cipher, either (i) the code- group is subtracted from the key, or (2) the key is subtracted from the code-group; and hence, in deciphering to obtain the code-group (1) the cipher is subtracted from the key or (2) the cipher is added to the key.

2. (in the case of periodic or running key substitution on plain language by means of a Vigenere square). A system of enciphering in which either (i) the plain Language letter is found at the beginning of a line (or top of a column), the key-letter in the square, and the cipher letter at the top of the corresponding column (or end of corresponding line), or (2) the key-letter is found at the beginning of a line (or top of a column), the plain language letter in the square and the cipher letter at the top of the corresponding column (or end of corresponding line). The processes involved in the two systems can be stated in equations as follows;

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