“A wise man is never surprised”: Decoding a 200 year old cipher

One of my responsibilities at Rauner is ingesting PDF scans of archival material into our digital repository for long-term preservation. If you request a scan of an entire folder from us, after it is delivered to you, it will almost certainly pass through my laptop. We scan and deliver thousands of pages of files a year, and I don’t read them all, but if something happens to spark my curiosity, I do like to take a look. This is how I came across this surprising find earlier this year. Hidden in Box 4 Folder 1 of the Dinsmoor family papers, I found a secret message.

This is what cryptographers call a grille cipher. In a grille cipher, the message is hidden in a grid of letters. Decoding the message requires using a stencil or grille with holes cut out, which, when aligned in the right spot on the grid, blocks the filler letters and leaves only the letters of the message visible.

It should go without saying that discovering a secret message hidden in a collection of 18th century papers is about as exciting a find as an archivist can make. It is basically the plot of National Treasure. I couldn’t help but wonder what piece of information was so sensitive that Silas Dinsmoor took the time to construct this cipher, writing out these letters in a neat grid and carefully cutting out all these windows. Buried treasure seemed unlikely, but maybe it was something else: a family secret, a confession, a message to allies in wartime? I was determined to decode it.

Unfortunately, the paper was fragile and creased, making it hard to flatten the grille and align the windows without tearing the page. Fortunately, we have access to a crack team of conservators here at Dartmouth Libraries, and they were able to repair the paper and make it usable again. Assistant Conservator Matt Zimmerman explains how he did it:

“I humidified it in a humidification chamber made from a photo developing tray for about 45 minutes; then I further humidified the more stubborn creases by brushing ethanol into them, then I put the whole piece under weight between spunbonded polyester and blotter; once dry and flattened, I mended any tears with a very thin (3gsm) remoistenable Japanese tissue.”

With the pages back from Preservation and carefully enclosed in protective mylar sleeves, I sat down to decode the message. Starting with corner A of the grille in the top left corner, I aligned the two leaves and started writing down the letters I saw. When I reached the end of the grid, I rotated the grille so that corner B was in the top left, then C, then D. Then I flipped the page and decoded the text on the back. It was exciting to see the message start to reveal itself:

It is a ma
xim com
monly rec
eived t
hat a wise
man is ne
ver surp
rised…

Readers, I am sorry to disappoint, but there was no secret confession or clues to buried treasure hidden in this cipher. It is just a Samuel Johnson quote. Why Dinsmoor decided to encode it we may never know. Perhaps he enjoyed the challenge. Perhaps he wanted to prank us from beyond the grave. 

To decode the rest of the cipher yourself, request MS-40 Box 4 Folder 1 and come to the reading room.

This post was written by Charlie Langenbucher, Processing Specialist at Rauner Library.