Cryptography Reference
In-Depth Information
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Figure 2.3:
Ciphering cylinders.
cylinders. In general, however, both the order of the disks in ciphering cylinders
and their selection from a larger set (e.g., 30 out of 100, corresponding to
approximately 3*10
25
possibilities) were secret. In World War II, the Japanese
failed to break a device known as CSP-642 with 30 sliders (algorithmically
equivalent to a ciphering drum), although they were in possession of several
sliders. In contrast, the US 30-stick device O-2 was broken by the German
Rohrbach [BauerMM, 7.4.3]. On the other hand, the Germans thought their
Enigma to be absolutely secure, an opinion the Poles and British didn't share
at all — see below! The level of cryptanalysis differed very much from one
country to another, and that's still the case today.
Rotor Machines
Rotor machines
are based on a much cleverer idea than ciphering drums.
With rotor machines, electric power came into play for the first time; they are
electro-mechanic encryption devices. Some descriptions of rotor machines are
hard to understand, while their principle is very simple. Let's look at it in steps:
•
Imagine a thick, electrically insulating disk. Twenty-six contacts are
arranged in a circle on its opposite faces. Every contact on the left side
is connected to exactly one on the right side, and vice versa, in some
secret way. This corresponds to a substitution.
