The 1944 Bletchley Park Cryptographic DictionaryPage 89 |
Tony Sale's Codes and Ciphers |
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TUNING MESSAGE :
TUNNY :
Each of the five chi wheels and each of the five psi wheels bears
a pattern which can be considered as a succession of ones and
noughts (in practice written as crosses and dots), the numbers
of ones on any of these wheels being as a rule approximately
equal to the number of noughts. In the chi wheels the
distribution of ones and noughts is more or less random, i.e.
any sign is as likely to be followed by the same sign as by a
different sign; but in the psi wheels there are usually
many more changes of sign than continuations, apparently in
order that the psi-wheel patterns should have an approximately
random sequence when extended by the motor. (cf. Turing's
method and motor).
Encipherment is effected by the addition (non-carrying) in the scale of two of each of the impulses of a letter to the signs of the appropriate chi and psi wheels which are at the operative position for that letter, the resulting five signs being transmitted as a teleprinter letter. This, on reception, operates, and is operated on by, an identical machine having its twelve wheels set in the same positions as the enciphering machine; and this by the same cycle of operations deciphers the letter and prints the clear equivalent on a tape.
2. Any traffic enciphered on the above machine.
TURING's METHOD :
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