Briscoe Center Works with Math Department to Decode Secret Confederate Message
A series of previously unintelligible Confederate telegrams in the Briscoe Center’s collections has been deciphered thanks to mathematicians at the University of Texas. The telegrams, which convey secret military intelligence to Confederate President Jefferson Davis, were written by Confederate General Kirby Smith in October 1864.
“The telegrams came to UT in the 1930s, and have — for all intents and purposes — been inaccessible to scholars and students,” said Don Carleton, executive director at the Briscoe Center. “Thanks to Andrew Blumberg at the UT Department of Mathematics, researchers at the Briscoe Center can now use the encrypted telegrams for research.”
Smith was commander of the Confederate Trans-Mississippi department, which included Texas. He telegrammed Davis’s Richmond headquarters using a “Vigenère cipher,” a common form of encryption used by the confederacy during the Civil War.
“There was something uncanny about watching these strings of gibberish resolve themselves into the words of a long dead general, knowing that no one had read these messages in a very long time — it was very exciting,” said Blumberg.
Previously, the eight telegrams were presumed to be individual communiqués between Davis and unknown subordinates. They are in fact, portions of a single message in which Smith notifies Davis that he has “failed after every effort” to move troops across the Mississippi River. Instead, Smith has moved forces to Arkansas in order to aid General Sterling Price’s Missouri Raid (an abortive Confederate attempt to recapture Midwestern territory and deal Abraham Lincoln a demoralizing blow during election season). Smith defends his actions, claiming they caused “the enemy” to dispatch troops from Mobile, Alabama, which subsequently “occupy a menacing attitude requiring all my force to oppose them.”
Preliminary analysis suggests that Smith’s overly-defensive tone was borne out of a justified anxiety that his military subordinates, particularly Richard Taylor, were undermining his position with Davis. Davis had made multiple requests of Smith to move forces east. However, bad weather, military caution (a criticism of Smith leveled by Taylor), and perhaps the desire to keep his fiefdom intact, had prevented Smith from complying.
The telegrams also detail Smith’s assertion that Union General Edward Canby had “assumed the offensive” along the Atchafalaya River in Louisiana, and that another Union force was “making demonstrations” close by. Smith ends with a belated commitment to send troops if “necessities east of the Miss. are so urgent” but he stresses that “no half measures be adopted, endangering the loss of this dept.”
“In short, the telegrams show a Confederate campaign in disarray, outnumbered by Union forces, and unable to maneuver troops without surrendering territory or endangering supply lines,” said Carleton.
Smith’s department was nicknamed “Kirby Smithdom” due to its isolation, bureaucracy and self-sufficiency. He was the last Confederate general to surrender—in Galveston, Texas (to Canby), at the end of May, 1865. Interestingly enough, he eventually became a professor of mathematics in Tennessee after a series of business failures in the telegraph business.
What is a Vigenere Cipher?
A Vigenere cipher is an enhanced version of a standard substitution cipher. Such ciphers “substitute” one letter for another according to a rule. (For example, “A=Z, B=X, C=Y” and so on.) If you know the rule, you can decode the message. If you don’t, you would need to deduce what the rule was by employing mathematical models.
Vigenere ciphers are more complex because the substitution at a given position in a message is controlled by a repeating key phrase rather than a simple rule. For example, if the coded message was “I-H-H-J” and the key phrase was ‘B-A-D’, the first character would be shifted by 2 letters (I to K), the second by 1 (H to I), the third by 3 (H to L), and the fourth by 2 again — revealing the message, “K-I-L-L.”
In other words, if you know the key phrase you can decode the message. Otherwise you would need to guess the key phrase using a combination of intensive calculations and patient guess work. (Union forces employed large teams of intelligence officers during the Civil War who worked to decode intercepted Confederate telegrams.)
With the aid of modern computers, sufficiently long messages encoded using a Vigenere cipher can be decrypted via statistical tests that guess the key phrase length. From there, one can use frequency analysis to break the code. Blumberg was able to decode the telegrams easily due to the fact that the Confederacy (in violation of cryptographic best practices) used only a small number of popular key phrases. Smith’s telegrams to Davis were encrypted using the phrase “Complete Victory.”