# The 1944 Bletchley Park Cryptographic Dictionary

### Page 55

Tony Sale's
Codes and Ciphers

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MIXED UNIT :

(of codes or code books). Having groups of more than one length, e.g. some 4-figure and some 5-figure groups.

MOCK-UP :

Reconstructed model or copy (of a machine, etc.).

MODULUS :

Scale or basis of arithmetic; that number which, or any multiple of which, is represented by 0, in any arithmetical system, (the number corresponding to the multiple being "carried" in ordinary, and ignored in cryptographic or "non-carrying" arithmetic); operations with figures are normally done with 10 as modulus, and operations with letters with 26.

MOTOR :

(in Tunny). The combined motor-wheel patterns together with any additional function (e.g. chi-2 or KTF) which regulate the movement of the psi wheels.

MOTOR-WHEELS :

(in Tunny). Those wheels, esp. the two wheels in the simplest model of the machine, whose patterns are combined to form the series of active and inactive contacts which determine the movement of the five psi wheels, and which therefore enter into the composition of all five of the single-impulse enciphering keys. The larger of the two (period 61) advances one position for each letter that is enciphered; and communicate this motion to the smaller (period 37) or not, according to whether an active or an inactive contact is being made at the time. The smaller wheel, either directly or after Boolean addition of one or more other components (see chi-2 function and KTF), moves the Psi wheels on one position when it has an active contact (represented by 1 for addition purposes) in the operative position, and does not move them when it has an inactive contact (represented by 0 for addition purposes) in the operative position, with the result that the last signs of the psi wheels are used again and the psi patterns characteristically extended.

MRS. MILES :

An electric tape-reading and tape-punching machine designed to read and add together up to four teleprinter tapes and punch the result on a single tape.

MONO-ALPHABETIC :

Involving or using only one alphabet.

MULTIPLE ANAGRAMMING :

Process of anagramming simultaneously several transposition messages of the same length that have been enciphered on the same key.

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