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

great deal of data and many pages of analysis, but that was the problem
faced daily by the cryptanalysts. The method can, however, be illustrated
using the data from the 12-point mini-Enigma example above. We
assume that the plugboard is known and that we have to see if any of the
known wheels at one of 12 possible starting positions could be R1. Since
there are many incorrect possibilities only two cases will be examined:
one incorrect and the other correct.
Example 9.3
The doublets in the 12-point mini-Enigma above are believed to have
been enciphered at consecutive wheel positions on a common groundsetting
with R1 having the encipherment table shown in Table 9.2.
Table 9.2
Setting
Input letter 1 2 3 4 5 6 7 8 9 10 11 12
A K A G L H F I C F D L E
B F L B H A I G J D G E A
C B G A C I B J H K E H F
D G C H B D J C K I L F I
E J H D I C E K D L J A G
F H K I E J D F L E A K B
G C I L J F K E G A F B L
H A D J A K G L F H B G C
I D B E K B L H A G I C H
J I E C F L C A I B H J D
K E J F D G A D B J C I K
L L F K G E H B E C K D J
Show that aligning the chains as
D AICJK
H BLFGE
The Enigma cipher machine 129
(1) leads to contradictions if we assume that R1 is originally at Setting 1,
but
(2) produces a solution if we take R1 to be originally at Setting 2.
Solution
(1) We begin by enciphering vertical pairs from the chain at Setting 1 and
diagonal (NW–SE) pairs at Setting 2. The 12 pairs that we obtain should
be consistent and provide the 6 pairs of the composite reflector: Table
9.3.