Civil War Cryptography

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A Brief Review of Cryptography During the Civil War

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 Square


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 clerk. 


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 code.”


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.