Cryptography Reference
In-Depth Information
native tongue. The native American languages are extremely complex, diQcult
to learn, and certainly for the Germans, nearly impossible to understand, so it
was an effective means of enciphering important data. In World War II, the
Americans similarly employed Navajos to transmit important messages in their
native language. They became known as the
Windtalkers
, the name of a Holly-
wood film, released in 2002, celebrating their achievements. The enemy never
broke the native codes.
On March 5, 1918, the famous German
ADFGVX
cipher went into service.
It was invented by Colonel Fritz Nebel, who was a communications oQcer in the
Kaiser's army. The cipher got its name from the fact that these were the only
six letters used in the cipher. These
specific
six letters were chosen since their
Morse code equivalents were suQciently dissimilar so as to minimize errors. To
convolute the cryptosystem, the Germans used a combination of substitution
and transposition techniques. This it how it worked.
THE GERMAN ADFGVX FIELD CIPHER
The Germans used a table (see Table 2.2) where the twenty-six letters of the
alphabet plus the ten digits (with 10 represented by
φ
) populate the six-by-six
square, where the coordinates of each letter and digit are uniquely determined
by the six letters. For instance, the coordinate of H is FX.
A D F G V X
A
B
3
M R L I
D
A
6
F
φ
8 2
F
C
7
S E U H
G
Z
9
D X K V
V
1
Q Y W
5
P
X
N J T
Table 2.2
4
G O
Thus, for instance,
The Germans are there
would be enciphered as:
XF FX FG XV FG AG AF DA XA
FF DA AG FG XF FX FG AG FG
However, this is only the
transitional
ciphertext, which was then placed in
another rectangle to be transposed into the
final
ciphertext using a numerical
key as follows. We think of the letters of the key
RADIOS
as having numerical
equivalents according to the alphabetic order of the letters, namely A corre-
sponds to 1 since it is the letter in RADIOS that appears first in the alphabet,
then D corresponds to 2, and so on. Then place the above transitional ciphertext
by rows into a matrix as follows in Table 2.3.
Search WWH ::
Custom Search