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I'm reading a recently-published and very
interesting history of cryptography by Simon Singh entitled "The Code
Book" (Anchor Books, ISBN 0-385-49352-3, $14 paperback.) One of first
chapters covers a virtually impregnable polyalphabetic substitution cipher that
was invented in the 16th century by Blaise de Vigenere--has anyone considered
possibility that the VMS is enciphered using the Vigenere system?
Singh does a much better job of explaining this cipher, but
basically an alphabet is written on consecutive lines, one on top of the other,
for as many times as there are letters in the alphabet. Each copy of the
alphabet, however, is shifted by one place, so that the first letter that
appears at the beginning of each line is different, like this:
ABCDEFGHIJKLMNOPQRSTUVWXYZ
BCDEFGHIJKLMNOPQRSTUVWXYZA CDEFGHIJKLMNOPQRSTUVWXYZAB
DEFGHIJKLMNOPQRSTUVWXYZABC
EFGHIJKLMNOPQRSTUVWXYZABCD
etc.
A keyword, such as WHITE, is then copied repeatedly above the
top alphabet, like this:
WHITEWHITEWHITEWHITEWHITEWHI
ABCDEFGHIJKLMNOPQRSTUVWXYZ
BCDEFGHIJKLMNOPQRSTUVWXYZA CDEFGHIJKLMNOPQRSTUVWXYZAB
DEFGHIJKLMNOPQRSTUVWXYZABC
EFGHIJKLMNOPQRSTUVWXYZABCD To encipher a word, each of its letters is located in the top
alphabet and correlated with whichever letter of the keyword lies above
it. That letter of the keyword in turn prescribes the exact copy of the
alphabet below, so that if the word BIRD is being enciphered, the letter B of
BIRD is associated with the letter H of WHITE (B is the second letter of the top
alphabet--the "base" alphabet, as it were--and the letter H of the
word WHITE appears above it.) This in turn specifies the alphabet row
beginning with H for the substitution. The second letter of the H alphabet
is G, so the letter G is substituted for the letter B of BIRD.
The advantage of this cipher is that it renders letter
frequency analysis useless, because frequently-appearing letters in the original
text will be enciphered with different letters throughout the
encryption.
This system would allow the space character to be enciphered
as well, so the apparent word breaks in the VMS may not be spaces between words
at all.
Charles Babbage was the first to discover a method of cracking
a Vigenere cipher (I won't go into that here--read the Singh book for the
surprising method.)
Has anyone approached the VMS from this
standpoint?
--Tom
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