Codes Contained in 1880s Dress Are Finally Cracked

Sara Rivers Cofield thought she was buying a pretty but unexceptional dress. In fact, she would soon discover the 1880s-era silk bustle dress, bought at a Maine antiques mall in 2013, had a secret pocket, inside of which was paper containing 23 handwritten lines of code. In a few cases, the first word of each line seemed to indicate a location, such as Bismarck and Helena. The rest "was just nonsense," says Rivers Cofield, a dress collector, who shared the codes on her blog in 2014, per the CBC. Over the next decade, online sleuths would try and fail to explain the meaning, speculating that the dress owner was a spy or illegal gambler, per the New York Times. Now, the "silk dress cryptogram," named among the world's top unsolved encrypted messages, has finally been solved.

Early on, cryptographers realized the messages were telegraph codes. In order to convey complex information via telegraph, thousands of code words were created to represent phrases and sentences. But cracking these particular codes proved difficult. "I went through 170 code books and I ended up not finding anything that matched this," Wayne Chan, a computer research analyst at the University of Manitoba, tells the CBC. Eventually Chan realized these were weather reports, beginning with what the CBC describes as "a non-encoded word as a locator." "Garry," for example, meant the Fort Garry weather station in Winnipeg. After much searching, Chan found explainers for the remainder of the text in a US Signal Service Weather Code book from 1887.

After the location came code words for temperature/pressure, dew point, precipitation/wind direction, cloud observations, and wind velocity/sunset observations. In the line "Bismark Omit leafage buck bank," traced to May 27, 1888, "omit" translated to air temperature of 56 degrees and a barometric pressure of 0.08 inches of mercury; "leafage" to a dew point of 32 degrees at 10pm; "buck" to clear weather with no precipitation and a north wind; and "bank" to 12mph wind velocity and a clear sunset. The last owner of the dress remains a mystery, though "my best guess is it is a woman who worked for the [Signal] Service office in Washington," where daily national weather reports were produced, says Chan, whose findings are published in the journal Cryptologia, per the CBC. (More code breakers stories.)