Cryptography Reference
In-Depth Information
letters until the cryptogram was completed.
The recipient would align the first 36 letters of ciphertext parallel to his
spindle as had the sender. Then at one of the other 25 rows would sit the
(obvious) plaintext. The process would be repeated for the remaining blocks of
36 letters each until the entire cryptogram was turned into the original plaintext.
Given the above delineation of how it worked, Jefferson's wheel cypher was
therefore a polyalphabetic cipher with the plaintext as the key, quite an amazing
invention for that time and, as we shall see, for some time to come.
His wheel cypher and his idea were filed away and completely forgotten until
1922 when it was rediscovered in the Library of Congress. It had been reinvented
many times and one of the forms was the U.S. Navy Strip Cipher, M-138-A,
used in World War II. In fact, many cryptanalysts in U.S. government agencies
in the early twentieth century could not cryptanalyze Jefferson's system! Thus,
Jefferson truly deserves the title
Father of American Cryptography
.
Wadsworth, Wheatstone, and Playfair
Yet another American invented a cipher disk, this one with gears. In 1812,
Colonel Decius Wadsworth was given a position as the first chief of ordnance
of the U.S. Army, a post he held until 1821. In 1817, while at this post, he
invented a device that was a brass cipher disk in a wooden container 6 and 1
/
2
inches in diameter and roughly 3 inches high. The outer alphabet had 26 letters
together with the integers 2 through 8 inclusive (33 symbols in all); and the
inner alphabet had just the original 26 letters. He included a brass plate with
two small openings that align to identify the plaintext and ciphertext equiv-
alents. The container itself enclosed two gears, (one with 33 and the other
with 26 teeth) to rotate the disks. To set up correspondence, the sender and
recipient merely agree on a sequence for the ciphertext and a starting point,
which would be a symbol in the brass plate opening for both plaintext and its
ciphertext chosen equivalent. For instance,
W
might be in the opening at the
outer disk, while
a
is at the opening of the inner disk. This introduced differ-
ing numbers of symbols for plaintext and ciphertext resulting in a progressive
cipher in which alphabets are used irregularly, depending on the plaintext used.
Thus, Wadsworth's device was a progressive system that was polyalphabetic.
The reader will recall that Trithemius also introduced a progressive key (see
page 52). However, Trithemius' progression was
regular
on 24 cipher alphabets,
whereas Wadsworth's progression was
irregular
on 33 cipher alphabets, much
more secure. Unfortunately for Wadsworth, his idea died with him, and credit
went to someone across the Atlantic.
Charles Wheatstone (1802-1875) worked on many areas from acoustics to
inventing the electric telegraph before Morse. His many achievements earned
him a knighthood in 1868. He also delved into the cryptographic arena. In
1867, at the Exposition Universelle in Paris, Wheatstone unveiled his
crypto-
graph
, which was essentially the same as Wadsworth's gear cipher, only a weaker
version. Wheatstone's device had an outer ring consisting of 27 plaintext sym-
bols (26 letters and a blank), and an inner ring with mixed ciphertext alphabet
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