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

156
chapter 11
in many books such as [11.1], [11.2] but, as a sample, sufficient for our
needs, we note that
A is 11000
B is 10011
...
P is 01101
Q is 11101
...
Z is 10001
41 31 29 26 23
61
37
43 47 51 53 59
Figure 11.1. Motion control in the SZ42. The 5 wheels at the top and the
61-wheel moved every time a letter was enciphered. The 61-wheel controlled
the 37-wheel which controlled all the 5 wheels at the bottom.
(there is no obvious relationship between representations of consecutive
letters of the alphabet).
Although the 61- and 37-wheels determined the motion of the wheels
in set C they played no direct part in the actual encipherment process,
which involved only the five binary components of the plaintext letter
and the current five pins of set A and the current five pins of set C.
A schematic diagram of the motion control in the SZ42 is shown in
Figure 11.1.
The encipherment of a letter on the SZ42 was carried out as follows:
(1) the plaintext letter, P, was converted to its five-bit binary equivalent in
the ITA code;
(2) the five bits of P were each enciphered separately;
(3) each bit of P was added (mod 2) to the value of the current pin on one of
the wheels of set A, the value being 0 for an inactive pin and 1 for an
active pin;