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

It should be realised, of course, that the example gives only an indication
of how messages on the original Enigma, with no plugboard and only
three wheels in the set, could be decrypted. Many changes were made to
the Enigma itself and to its operational procedures, particularly during
the years 1938–45. For example:
(1) the repetition of the three-letter indicator was modified by the
insertion of a pair of dummy letters and the use of a digraph
substitution table;
(2) the use of a common ground setting was abandoned; operators chose
their own ground setting which they gave, unenciphered, at the start
of the cipher text;
(3) the three wheels were increased to five by all users and later to eight by
the German Navy, who also used a four-wheel Enigma from 1942,
which involved a new reflector.
These changes provided the cryptanalysts at Bletchley with a series of
formidable challenges, which were overcome, in some cases quickly but
for the four-wheel machine only with great effort.
For more information see [9.2] and [9.3].
Anyone interested in simulating the Enigma on a PC and following
the steps of the original Polish solution would find [9.4] interesting.
For those who would like to try setting a (mini-) Enigma wheel here is:
Problem 9.1
On a 10-point mini-Enigma which has been used to encipher messages
based on the digits 0–9 the results of enciphering the doublets 00, 11, ...,
99 at the same ground setting are obtained from the indicators (in
unknown order) and are
(0, 2), (1, 6), (2, 3), (3, 9), (4, 8), (5, 5), (6, 4), (7, 7), (8, 1) and (9, 0).
The first column of the encipherment table of the wheel which is believed
to be R1 is
(0, 8, 6, 4, 3, 7, 1, 5, 9, 2).
The Enigma cipher machine 131
Complete the encipherment table and, with a suitable alignment of the
chains, verify that R1 at setting 3 is consistent with the data. What are the
pairings in the composite reflector?