Keeping Secrets, Part 2: Route Ciphers

 

By Daniel Stowell, Director and Editor of the Papers of Abraham Lincoln at the Abraham Lincoln Presidential Library and Museum.

Maintaining the secrecy of high-level political and military communications during the American Civil War was a necessity for both the Union and the Confederacy.  In the previous post, we learned that the Union had the advantage of a simple but ingenious system developed by Anson Stager, the civilian superintendent of the Western Union Company in Ohio.  Early in the war, Stager developed a cipher system for use by the governor of Ohio and Union generals in the area.  When he became the head of the United States Military Telegraph in October 1861, Stager brought his cipher system with him and used it throughout the Union high command.

Stager’s system depended on absolute secrecy, and not even top civilian or military officials were allowed to see the cipher codes.  The cipher Stager developed relied on two key principles.  First, a cipher telegrapher replaced key nouns and verbs for persons, places, and military terms with arbitraries, or code words, known only to his counterpart at the other end of the telegraph line.  Although this technique was effective, so long as the cipher remained absolutely secret, over time, dedicated Confederate agents who intercepted such messages might be able to guess at the true meaning of many or most arbitraries.

However, Stager’s system had another key component.  It was also a sophisticated “route cipher.”  At its simplest, a route cipher simply reorders the words in a message from their ordinary reading order.  For example, a backwards route would simply reverse the order of all words in the message, and the recipient could read the message from the end to the beginning to understand it.  The system employed by the Union during the American Civil War was substantially more complicated.

The key to decoding a route cipher is to place the words in the proper number of rows and columns, similar to a modern-day spreadsheet.  The key unit in Stager’s system was the word, not the letter.  So, a cipher telegrapher would take a message and write it out in a series of rows and columns.  If the message did not end on the last column of the last row, he would add additional “null words” to fill out the grid.  These null words could be nonsense or they could even send a short message to his counterpart on the other end of the line, such as “Nab those Rebs” and “Rained nicely tonight.”

After the message was arranged in a grid, the cipher telegrapher chose a route through the grid to reorder the words.  For example, if the message was 10 columns wide by 11 rows long, then the cipher telegrapher could use the commencement word “Morton” (among others) to indicate that the message had 10 columns and the commencement words “Next” or “News” to indicate that it had 11 rows (2 rows + 9 rows).  The receiving cipher telegrapher consulted his cipher 1 code book and knew that the incoming message of 110 words should be arranged in 10 columns and 11 rows.  Then, he placed the words in their proper order by reading the route indicated in cipher 1: down the sixth column, down the tenth column, up the first column, down the eighth column, up the second column, down the fourth column, up the seventh column, down the third column, up the fifth column, and down the ninth column.

Reading the words in this manner placed them in their proper order, but the receiving cipher telegrapher still needed to replace the arbitraries in the message with their clear counterparts, either words or punctuation.  The telegrapher also stripped out the commencement words and the null words to leave only the words of the message.

The scrambling of words through the route cipher method made Stager’s system far more difficult to decipher than using arbitraries alone.  In fact, the Confederates never broke any of the Union ciphers, and the ability for political and military leaders to communicate important information securely was important to the overall success of the Union war effort.

Fortunately for researchers, none of the telegrams in the Thomas T. Eckert Papers are scrambled in the route in which they were originally sent.  Even those with arbitraries for words and punctuation are in their proper order, making decoding them a much simpler task than Confederate agents faced in the 1860s.

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