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KEYBREAKER :
Person occupied in solving the keys or subtractors used in any type of
cipher, esp. reciphered codes.
KEY-BREAKING :
The action or process of discovering or "recovering" cipher keys or
subtractors.
KEY-DIFFERENCING :
Method of key-breaking (esp. with machine keys) consisting in sub-
tracting a length of key from itself at a particular interval with a
view to eliminating the component whose period is equal to that interval.
KEY-GETTER :
KEY-GROUP :
The series of key-figures used to recipher one particular group of a
message or one particular column of a depth, or the value provisionally
assigned to this; (spec.) the group of key-figures used to encipher an
indicator.
KEY-INDICATOR :
KEYING FIGURE :
A figure constituting or denoting the recipher key used, esp. a short key.
KEY-LENGTH :
The length of the key used, esp. in Transposition systems.
KEY-LETTER :
(in poly-alphabetic ciphers). The letter which determines which of
the available cipher alphabets is used to encipher a particular letter
of plain-language.
KEY-SQUARE :
1. (in Playfair systems). The arrangement of 25 letters in a square
which constitutes the key, or part of the key.
2. (in polyalphabetic ciphers). The table of substitution alphabets
used, normally forming a square, 26 by 26, with the key-letters
along the top, the plain letters down the side, and the cipher-
letters in the square itself; but see Beaufort system.
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