I’ll probably never get tired of writing blog posts about cryptography. It’s a puzzly skill with plenty of real-world applications. Heck, England hosts a yearly codebreaking challenge in order to identify people with topnotch cryptographic abilities in the hopes of recruiting them for government work!

We’ve explored how modern codebreaking has cracked secret messages from the Civil War as well as how cryptographic skill caught a murderer and helped decipher the lost language Linear B. We’ve even talked about the time that enterprising codebreakers saved Christmas!

And, as it turns out, a nineteenth-century codebreaker may have solved the mystery of the Man in the Iron Mask.

For centuries, French communiques were unreadable because the French employed Le Grand Chiffre, or the Great Cipher, a substitution code devised by Antoine and Bonaventure Rossignol that employed numbers standing in for letters. (There were several variations of the Great Cipher, ranging between 580 and 720 code numbers.)

But the Great Cipher was cracked by Etienne Bazeries, a French military cryptoanalyst who deduced that each number stood not for a single letter, but for pairings of letters. More specifically, syllables. Over the course of three years (from 1891 to 1893), by working his way through the patterns and identifying common letter patterns based on frequency of use, he deciphered first a few words, and eventually, the entire cipher. (Supposedly the key was the numeric combination “124-22-125-46-345,” which stood for “the enemies.”)

One of the encoded messages from King Louis XIV concerned a disgraced general named Vivien de Bulonde, who endangered an entire French campaign against the Austrians by fleeing an Italian town instead of attacking it.

His Majesty knows better than any other person the consequences of this act, and he is also aware of how deeply our failure to take the place will prejudice our cause, a failure which must be repaired during the winter. His Majesty desires that you immediately arrest General Bulonde and cause him to be conducted to the fortress of Pignerole, where he will be locked in a cell under guard at night, and permitted to walk the battlement during the day with a 330 309.

Bazeries believes that “330” and “309” stood for the syllables “mas” and “que,” meaning that General Bulonde was masked for his daily walks, but since those Great Cipher codes were apparently only used once, it’s impossible to confirm Bazeries’ suspicions.

It took Bazeries three years to crack an “uncrackable” code, and quite possibly solve a centuries-old mystery. Another testament to where puzzly skills can take you.

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