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

P1
41
43
Z1
(4) the five bits from stage (3) were added separately (mod 2) to the value of
the current pin on one of the wheels of set C, the value being 0 or 1 as at
stage (3);
(5) the resulting five-bit character, Z, was converted back, via the ITA
code, to give the cipher letter on a printing mechanism;
(6) each wheel moved in accordance with the motion control mechanism.
The encipherment of each stream depended on just 2 of the 10
wheels: 1 from set A and 1 from set C. For example, the first stream was
enciphered by the 41-wheel in set A and the 43-wheel in set C, whilst the
fifth stream was enciphered by the 23-wheel in set A and the 59-wheel in
set C.
A schematic diagram of the encipherment process on the SZ42 is
shown in Figure 11.2.
As only (mod 2) addition of the plaintext and keys was involved the
processes of decipherment and encipherment were identical since addition
and subtraction are the same (mod 2).
As an illustration of the encipherment process:
Example 11.1
If the pin values on the wheels of sets A and C are
Set A 0 1 0 1 1
Set C 1 0 0 1 0
P2
31
47
Z2
P3
29
51
Z3
Beyond the Enigma 157
Figure 11.2. Encipherment process in the SZ42. The five streams of the
plaintext letter, P, were separately added (mod 2) to the bits produced by the 2
corresponding wheels below to produce the five streams of the cipher letter Z.
and the plaintext letter is S (�10100 in ITA) what will be the cipher
letter? Verify that decipherment yields the original plaintext letter.
P4
26
53
Z4
P5
23
59
Z5