Dress code: How a Winnipeg codebreaker cracked one of the ‘world’s top unsolved messages’

"Bismark Omit leafage buck bank."

That seemingly random string of words appears in something called the Silk Dress cryptogram, 23 handwritten lines on two sheets of crinkled paper that were discovered in a hidden pocket of a Victorian-era dress bought in Maine in 2013.

The lines seemed like an encoded message from the late 1800s, with references to North American cities, including Calgary and Winnipeg.

"There were lots of theories [about its meaning], from the American Civil War to simply instructions for dress-making," said Wayne Chan, a University of Manitoba computer research analyst.

For about a decade, it stumped the global cryptanalytic community and was even listed as one of the "World's top 50 unsolved encrypted messages" on the cryptology blog Cipherbrain.

Chan says he was drawn to the mystery. "Why did this woman have a bunch of secret codes in this pocket in her dress?"

He cracked it in February, and his conclusions were published in the cryptology journal Cryptologia.

A dress with a secret

The mystery of the Silk Dress cryptogram starts in 2013 in Searsport, Maine, when dress collector Sara Rivers-Cofield decided to buy a long, flowing 1880s-era silk bustle dress she had been eyeing at an antique mall.

"I knew it had been there for a while," she told CBC. "I brought it home with my mom and it was sort of the newest big-deal acquisition for my collection."

When they examined the dress to figure out how it was put together, Rivers-Cofield and her mother found two pieces of crumpled paper concealed in a secret pocket under the overskirt.

"It's a bit of a private spot — it almost seems like it was protected," she explained. "It said 'Bismark Omit leafage buck bank.' It was just nonsense. So we were like, what's going on?"

She put it on a dress collecting blog she ran at the time.

"It's certainly the most popular blog post I ever did, because the code-cracking community picked up on it pretty quickly," she said. "Somebody said, 'That's a telegraph code.'"

Still, it would take nearly a decade for someone to solve it.

Cracking the code

Telegraph codes are all but forgotten today, but in the late 1800s, they were ubiquitous as the telegraph became the predominant means of rapid long-distance communication.

Thousands of codes were developed that allowed a word, a phrase or a sentence to be represented by a single code word.

It didn't just make messages shorter and cheaper to send, it was also secure. Unless you had the right code, the messages would simply appear as a random string of words, even as they passed through many hands.

Chan said that when he started looking into the Silk Dress cryptogram, "I went through 170 code books and I ended up not finding anything that matched this."

The key was to nail down when the message was written. The dress was a big clue.

Rivers-Cofield was confident from the machine stitching, buttons and overall style of the dress that it dated to the 1880s. That helped Chan narrow his search to a specific time, but he still ended up hitting dead ends after looking through dozens of Canadian and American university archives.

"I thought, I need to immerse myself in the era of the telegraph more, I need to understand how it was used," he explained.

What struck Chan was how the style and structure of the Silk Dress cryptogram resembled weather messages he found in his research — typically lines of five to seven words that began with a non-encoded word as a locator.

That led him to call the archives of the National Oceanic and Atmospheric Administration (NOAA) in Washington, D.C., where a copy of the 1892 U.S. Signals Service Weather Code confirmed his theory.

"I could tell it was clearly the right code — it didn't match exactly but about 90 per cent of it fit," Chan said.

A little more research led him to an 1887 version of the signals code that matched.

A cold spring day

Turns out "Bismark Omit leafage buck bank" was a weather observation for May 27, 1888, in what is today Bismarck, N.D.

The way the U.S. Signal Service Weather Code worked was each word in each line corresponded to either a location or a set of observable conditions.

When a weather reading was taken, it would be matched to a predetermined word in the codebook, and that word would be transmitted.

In the Silk Dress cryptogram, the first words of each line weren't encoded, so Bismark was the locator for the weather station.

The second word, Omit, corresponded to an air temperature of 56 F and a barometric pressure of 0.08 hg.

"Leafage" meant the dew point was 32 F at 10 p.m. "Buck" described clear skies, no precipitation and a north wind. "Bank" meant wind velocity of 12 mph.

Cross-referencing a map of telegraph routes, Chan believes these were daily observations relayed from far-flung weather stations down the line to Washington, where the U.S. Army Signals Service produced daily national weather reports.

"For the first time, the telegraph allowed news about the weather to travel faster than the weather itself," Chan said.

At the time, the U.S. and Canadian governments had an agreement to exchange weather information by telegraph.

That's how names of Canadian cities got into the Silk Dress cryptogram.

It includes observations from stations in Calgary, Minnedosa, Man., Winnipeg and Prince Arthur's Landing — modern-day Thunder Bay, Ont. — which all shared a telegraph line that connected to Milwaukee, Wis., and routed messages to Washington through New York.

This line described a cool spring day at the Fort Garry weather station in Winnipeg:

"Garry Noun Tertal lawful palm novice event."

According to the code, Garry listed the weather station. "Noun" was the day of the month, the 27th. "Tertal" was 42 F, with barometric pressure 0.94 hg. "Lawful" was humidity of 30 per cent at 10 p.m. "Novice" meant stratus clouds with 8/10ths cover. "Event" meant cloudy with wind velocity of 0-4 mph. The word "Palm" doesn't appear in the code; Chan believes it wound up in the message by mistake.

Calgary, meanwhile, was a little cooler that day, 40 F (4 C) and clear, while Thunder Bay was 46 F (7 C), as a northeast wind blew on Lake Superior.

So not exactly classified information.

Code cracked but mystery remains

Who owned the dress, and why was a seemingly benign message concealed for more than a century in a secret pocket?

That part of the mystery still eats away at Chan.

"My best guess is it is a woman who worked for the Signals Service office in Washington," he said.

The explanation could be as mundane as someone forgetting about a piece of paper left in their pocket at the end of the day, and by chance the dress was packed away, the message long forgotten.

"Were they just pieces of scrap paper?" Chan wondered.

The dress does offer a possible hint: a label that reads "Bennett." But Chan found no record of a Bennett employed at the Signals Service in Washington at that time.

Rivers-Cofield, who is also an archeologist, is equally fascinated and perplexed by the history here.

"I'm sure it would be much more fascinating, and blow up in a much bigger way, if it was a secret code to do with some war or spy or whatever," she said.

She points out that at the very least, the mystery offers insight into the time.

"Honestly, I feel like it's much more eye-opening to think about what knowing the weather meant to people … for the first time."

Chan, meanwhile, isn't giving up yet. He says he still has a few avenues to pursue that may help crack the dress owner's identity.