The 1944 Bletchley Park Cryptographic Dictionary
Codes and Ciphers
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1. (in reciphered codes). A series of figures usually in random order and, in the case of high-grade ciphers, of very great length, a portion of which (denoted by the indicator) is applied figure by figure, non-carrying, to the figures of the encoded message, either by addition or subtraction. Short keys and sometimes, in the case of long keys, single pages of key are treated cyclically when the end is reached; a subtractor. A vary short key is called a "recurring key".
b. The group of key-figures used to recipher any one code-group of the message; also, a provisional evaluation of this, properly termed "provisional column subtractor", or "provisional subtractor group".
c. (spec.) The key-group used to encipher an indicator.
2. (in Transposition). A series of natural numbers (i.e. from 1 onwards) arranged in non-numerical order (often obtained from a plain-language "key-phrase" ) which determine by their number the length of the cage used in transposition and by their order the sequence in which the columns are taken out of the cage in the process of encipherment and written in the process of decipher- ment.
3. (in Playfair systems). The order in which the letters of the alphabet are placed in the square or squares used.
4. (in Enigma). The wheel-order, ringstellung, stecker, and discriminants (if any) used by a particular group of stations on a particular day or other fixed period.
(n.) a keyboard indicator.
2. The novel or other book used as the running-key in Poly-alphabetic substitution ciphers.
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