“Bismarck Omits Leafage Buck Bank.”
This seemingly random string of words appears in something called the Silk Dress cryptogram, 23 handwritten lines on two sheets of paper found in a hidden pocket of a Victorian-era dress bought in Maine in 2013.
The lines appeared to be a coded message from the late 1800s, referencing North American cities including Calgary and Winnipeg.
“There were many theories [about its meaning]From the American Civil War to just sewing instructions,” said Wayne Chan, a computer research analyst at the University of Manitoba.
For nearly a decade, it puzzled the global cryptanalytic community and was even listed in the “World's 50 Best Unsolved Encrypted Messages” by the Cryptology Blog. Digit brain.
Chan says he was drawn to the mystery. “Why did that woman have a bunch of secret codes in that pocket of her dress?”
He cracked it in February and his findings were published in the cryptology journal Cryptologia.
A dress with a secret
The mystery of the Silk Dress cryptogram began in 2013 in Searsport, Maine, when dress collector Sara Rivers-Cofield decided to buy a long silk dress from the 1880s that she spotted at an antique mall.
“I knew he was there for a while,” he told the CBC. “I brought it home with my mom and it was kind of the latest big acquisition for my collection.”
When they examined the dress to see how it was fastened, Rivers-Coffield and her mother found two pieces of crumpled paper hidden in a hidden pocket under the skirt.
“It's a bit of a private place – almost like it's been protected,” he explained. “It read ‘Bismark Omit foliage buck bank.' It was just stupid, we were like, what's going on?”
She posted it on the dress collecting blog she was running at the time.
“It's definitely the most popular blog post I've ever done because the code-breaking community picked it up pretty quickly,” he said. “Someone said, ‘It's a telegraph code.'
And yet, it would take almost a decade for anyone to solve it.
Crack the code
Telegraph codes are largely forgotten today, but in the late 1800s they were ubiquitous as the telegraph became the primary means of rapid long-distance communication.
Thousands of codes were developed that allowed a word, phrase, or sentence to be represented by a single code word.
Not only did it make sending messages short and cheap, it was also secure. If you didn't have the right code, the messages would just appear as a random string of words, even when they passed through many hands.
Chan said that when he started looking into the Silk Dress cryptogram, “I went through 170 code books and in the end I couldn't find anything that matched it.”
The main thing was that the message was written. The dress was a big clue.
Rivers-Coffield was certain from the machine stitching, buttons and general style of the dress that it dated from the 1880s. That helped Chan narrow his search to a specific time, but he still hit a dead end after scouring dozens of Canadian and American university archives.
“I thought, I need to delve more into the age of the telegraph, I need to understand how it was used,” he explained.
What struck Chan was how similar the style and structure of the Silk Dress cryptogram was to the weather messages he found in his research—usually strings of 5-7 words beginning with a non-code word as a locator.
This prompted him to call the archives of the National Oceanic and Atmospheric Administration (NOAA) in Washington, D.C., where a copy of the 1892 US Signal Service Weather Code confirmed his theory.
“I could tell it was obviously the right code — it wasn't an exact match, but it was about a 90 percent match,” Chan said.
A little more research led him to the 1887 version of the signal code, which matched.
A cold spring day
It turns out that “Bismark Omit foliage buck bank” was a weather observation for May 27, 1888 in present-day Bismarck, ND.
The way the US Signal Service Weather Code worked was that each word in each line corresponded to a location or set of observable conditions.
When a weather reading was received, it would match a predetermined word in the codebook and that word would be transmitted.
In the Silk Dress cryptogram, the first words of each line were not coded, so Bismarck was a weather station locator.
The second word, Omit, corresponded to an air temperature of 56 F and a barometric pressure of 0.08 Hg.
“Leaf” means the dew point was 32 F at 10 a.m. “Buck” described clear skies, no precipitation, and a northerly wind. A “bank” meant a wind speed of 12 mph.
Cross-referencing a map of telegraph routes, Chan believes these were daily observations transmitted from distant weather stations to Washington, where the US Army Signal Service produced national weather information.
“For the first time, the telegraph allowed weather news to travel faster than the weather itself,” Chan said.
At the time, the US and Canadian governments had an agreement to exchange weather information by telegraph.
That's how Canadian city names got into the Silk Dress cryptogram.
It includes observations from landing stations in Calgary, Minnesota, Mann, Winnipeg and Prince Arthur – modern Thunder Bay, Ont. – all shared a telegraph line connecting Milwaukee, Wis. and sent messages to Washington through New York.
This line describes a cool spring day at the Fort Garry weather station in Winnipeg:
“Gary Noun Tertal Legal Palm Novice Event.”
According to the code, Gary listed the weather station. The “noun” was the day of the month, the 27th. The “tertal” was 42 F, with a barometric pressure of 0.94 sg. “Legal” was 30 percent humidity at 10 p.m. “Novice” means stratus clouds with 8/10 cover. “Event” meant cloudy with wind speeds of 0-4 mph. The word “palm” does not appear in the code; Chan believes it ended up being a mistake in the message.
Meanwhile, Calgary was slightly cooler that day, 40 F (4 C) and clear, while Thunder Bay was 46 F (7 C) as northeast winds blew over Lake Superior.
So not exactly secret information.
The code is cracked, but the secret remains
Who did the dress belong to and why was the seemingly benign message hidden in a secret pocket for over a century?
At least this part of the secret seems to eat.
“My best guess is that this is a woman who worked in the Signal Service office in Washington,” he said.
The explanation could be as mundane as someone forgetting a note left in their pocket at the end of the day and accidentally packing a dress, the message long forgotten.
“Were they just pieces of scrap?” Chan was surprised.
The dress does offer a possible clue: a label that says “Bennett.” But Chan could find no record of Bennett, then employed by the Signals Service in Washington.
Rivers-Caufield, who is also an archaeologist, is equally fascinated and confused by the history here.
“I'm sure it would be a lot more fascinating and blow up in a much bigger way if it was a secret code to do with something like war or espionage or whatever,” he said.
At the very least, he notes, the mystery offers insight into time.
“Honestly, I feel it's much more fascinating to think about what knowing the weather meant to people… in the first place.”
Meanwhile, Chan is not giving up just yet. He says he still has a few leads that could help identify the dress' owner.