Cryptography Reference
In-Depth Information
By the way, this section also ends with the sad comment that even the simple
bitwise Vigenere method is still in use: up to Version 5, the popular text proces-
sor WordPerfect used a slight modification of it (more about this in Chapter 3).
And WINCRYPT joined the list of highly insecure methods: it used a 512-byte
Vigenere key. According to [SchnCr, 1.3], the Vigenere method is still thought
to be heavily used in commercial software.
2.5 Domain of the Militaries: Ciphering Cylinders,
Rotor Machines, and the Enigma
Rotor machines have played an important role in the last century, both for
militaries and in cryptanalysis. We will first have a brief look at their precur-
sors — ciphering cylinders — and then have a closer look at the Enigma, the
most famous rotor machine.
Ciphering Cylinders
Computers have become so matter-of-fact for all of us that we consider some
things to be simple while they actually became simple only with the help of
computers. One of these things is polyalphabetic substitution. Back when every-
thing was done by hand it was deemed too difficult and error-prone. The first
mechanization came in the form of ciphering cylinders. A
ciphering cylinder
is an apparatus consisting of a set of disks with a different alphabet on the
edge of each disk, i.e., permuted alphabets in arbitrary sequence. Each disk is
responsible for a different permutation. For example, if you have 30 such disks
at your disposal, you turn them against each other such that 30 characters of the
plaintext appear in one line. The ciphertext is read from the line above or below
it, or from an arbitrary line. The code breaker sets 30 ciphertext characters on
the cylinder and finds the plaintext in another line. The order of the disks is the
key (with 30 disks, that results in 30! or approximately 2.6*10
32
possibilities).
Of course, the method is not secure by current standards, particularly if an
attacker has somehow come into possession of such a device, which always
happens sooner or later. Frequency considerations (and using other methods;
see Chapter 3) would then allow him to easily determine what disk is in which
place.
As always, such devices were used for longer than the level of cryptanalysis
would suggest. A well-known ciphering machine was the M-94 of the US
Army, which was in use at least from 1922 to 1943. It consisted of 25 aluminum
