The words “cryptography”
and “cryptology” are defined as the science or study of secret writing, especially code and cipher systems. Simple ciphers were used by the Spartans and the Romans for military communication
more than 2,000 years ago. After the fall of the Roman Empire, interest in cryptography
lessened and was not revived until the Renaissance. More advanced methods were
developed during the sixteenth and seventeenth centuries, one by a man named Porta.
Origins of the Vicksburg
Prior to Porta, most ciphers involved the simple substitution
of one letter for another. Porta created a cipher in which the use of a key word or phrase made the message difficult to read
because the replacement symbol for each letter kept changing constantly. His
method was published in 1563 and was then improved by Virgenère in 1587. Virgenère’s
table was adopted by the Confederates and became known as the Vicksburg Square. The
system is easy to use and requires the codeword (which determines how letters are replaced) and a cipher square by the cipher
The Confederates made the mistake of using only three
codewords (Manchester Bluff, Complete Victory and Come Retribution) during the entire war.
The Union had three young men in Washington named Bates, Tinker and Chandler who not only ciphered and deciphered the
Union’s messages, but also broke Confederate messages which had been wiretapped and captured from messengers. They successfully deciphered the Vicksburg Square system. President
Lincoln often watched them as they worked on a deciphering.
The Confederates also used multiple ciphering systems during the
war, leading to more confusion. General Johnston used a dictionary system while
General Beauregard used monoalphabetic substitution. In the dictionary system,
both the sender and the recipient held copies of the same dictionary with all the words numbered consecutively. Messages were sent by substituting the corresponding number for the desired word.
Telegraphs and Ciphers
The invention of the telegraph gave the military a rapid means
of communicating with their forces without having to worry about capture of couriers or having the enemy intercept an open
signal. The first Morse code, different from the one used today, was really a
cipher. In a code, a complete word or phrase is replaced by a single meaningless
word, while in a cipher, one symbol or letter replaces another, sometimes through several intermediate shifts. Code words may also be enciphered to make a message more difficult to read.
Since telegraph lines could be tapped, military information was not only ciphered, but encoded.
The Union’s Use of Route Ciphers
Route ciphers were the most commonly used method of secret writing
used by the Union Army. Invented by the general manager of Western Union, Anson
Stager, the route cipher ensured that unintended recipients could not read messages sent and received by the Ohioan governor,
William Dennison. In the route system, a message was written in a number of columns
of so many words each, which were read up or down in and in a random order, thus scrambling the message’s meaning. The key was given by a prearranged first word that informed the receiver how many
columns of how many words and in what sequence to restore the original message.
To further confuse the enemy, frequently used words such as Grant, Lincoln and Washington were replaced
with codewords. At the beginning of the war, all cipher information could be
contained on the back of a card. As the war progressed, the routes became more
complicated. By war’s end, there were 12 pages of route indicators and
36 pages for the 1,600 codewords used. The Southerners never deciphered the route
system. The coded messages were printed in various newspapers in the hope that
one of their readers might find a solution.
The Signal Corps and Cryptography
The Signal Corps also dealt with ciphers because the messages
were translated from letters into numbers then signaled. Col. Albert Myer was
the Union’s expert and he included a section on cryptography in is book, A Manual
of Signals. He described various methods for transferring letter into signals
that could be sent by flags, lights, sounds, etc. Information passed on by flags
and torches was usually of a tactical nature and the ability to transmit it quickly did play a part in some of the major battles.
In early April of 1863, Gen. Hooker’s men learned from a
captured Confederate officer that the Rebels knew the Federal signal code. The
messages themselves were unenci-phered, so once the alphabet was recognized, the messages could be translated.
Months before, the Federals had reconstructed the Confederate
alphabet, which also was not enciphered. Edwin Fishel, in The Secret War for the Union, assesses the situation as follows: “Even
the ability to read the Federal’s traffic, however, did not put the Rebels on the same capability level with their enemy,
for they virtually eliminated the value of their accomplishment by revealing it in their own messages ... The Federals knew
the enemy code but did not know [until then] either that the enemy was aware of that fact or that the enemy could read their
Col. Albert reacted by providing the signalmen with a cipher in
which letters were substituted for each other. The pairings were changed daily
and repeated weekly. Necessary paraphernalia for this could be carried in a pocket
and if lost or destroyed, it could still be reproduced from memory. The Union
signalmen went from one to seven alphabets and no evidence has turned up that the Confederates penetrated the new system.
Sources: Fishel, Edwin.
The Secret War for the Union. New
York: Houghton Mifflin Co., 1996.
Markle, Donald. Spies and Spymasters
of the Civil War. New York: Hippocrene Books, 1994.
Stern, Philip Van Doren. Secret
Missions of the Civil War. New York: Bonanza Books, 1959.