Code and ciphers: Julius Caesar, the Enigma and the internet

first day of usage and so the assessment of the security of the original
Enigma must be based upon the figure not of
but of
10 87
105 456
cases to be considered which, in 1923, before the invention of the computer,
might have been considered adequate for a machine intended for
purely commercial use. The German military, however, did not think so
and insisted upon certain changes which improved the security considerably,
the most significant of which was the introduction of
The Enigma plugboard
The military version of the Enigma included a plugboard at the front,
below the typewriter keyboard. This plugboard had 26 sockets that could
be connected in pairs by means of 13 short cables. The effect of this was to
interchange pairs of letters at both the input and the output stages. So, for
example, if A was connected to W by a cable then whenever the cipher
operator typed an A it would go into the Enigma as W, and vice versa.
Similarly a cipher letter which emerged from the final wheel, R1, as A
would light up the W lamp and so be recorded as W. The number of ways of
pairing the 26 letters of the plugboard is the same as the number of possible
Reflector wheels, i.e.
more than 10 12
and since the pairings on the plugboard were changed frequently (daily at
first and thrice daily from 1944) this increased the problem for the cryptanalysts,
who were now faced with having to consider more than 10 17
possibilities instead of 105 456.
The Achilles heel of the Enigma
The Enigma cipher machine 121
The internal wirings of the three wheels and reflector on the military
version of the Enigma were, at the understandable insistence of the military,
different from those on the original civil version of 1923, so that possession
of a 1923-version civil Enigma would not help the cryptanalysts. In
addition the plugboard had been introduced. Even if a cryptanalyst had