Most people know Lewis Carroll (the pen name of Charles Lutwidge Dodgson) as the author of Alice 's Adventures in Wonderland. Dodgson became good friends with the family of one of his academic colleagues, the Liddells, and would often take their children along with him when he went rowing on the nearby rivers. During these expeditions he would make up fanciful tales to entertain the children, and one of the girls, Alice, was so enchanted that she begged Dodgson to write it all down. The enthusiastic reception for the manuscript by fantasy author George MacDonald and his children convinced Dodgson to pursue publication. Dodgson's private life has been the subject of intense speculation, especially regarding his relationship with the Liddells. (Dodgson's family apparently destroyed several pages of his diary, presumably to protect his reputation.) We know that he was tormented by feelings of guilt and shame, which apparently restrained him from following his father into the priesthood. It's all very mysterious. One thing that's beyond any doubt though is that Dodgson demonstrated brilliance in many different fields. Notably, he held a lectureship in mathematics, and wrote books on logic. It's those abilities that he puts to good use in our next adventure.
It was in the fall of 1891 that I received a telegram from the Reverend Charles Dodgson, inviting me to his residence in Guildford, Surrey. It was not for a medical consultation, but of vital importance to the present trial of the Moriarty gang: the mystery of Professor Moriarty's cipher.
Reverend Dodgson was both an author of children's books and a mathematician. My wife was fond of the Alice books under his nom-de-plume, Lewis Carroll, while Holmes once recommended me to read his Game of Logic to hone my analytical reasoning. It surprised me that Dodgson knew of the coded notebooks, as their existence had been suppressed. It was not five months ago that my friend Sherlock Holmes perished at Reichenbach Falls in his final confrontation with James Moriarty. Even in death, Holmes struck a fatal blow against Moriarty's criminal confederates, leaving documents that thoroughly incriminated them. Inspector Patterson invited me to examine the materials recovered from one of Moriarty's secret lairs: vials of opiates among blueprints and handwritten musical scores; purloined paintings beside burned account books; and most intriguing, notebooks written in Moriarty's hand, the oldest of which had a page torn out.
Moriarty's notebooks contained mathematical formulae interspersed with code. Mycroft Holmes speculated it was a Vigenère cipher, but even he couldn't solve it. "Alas, both the Kasiski and Kerckhoffs methods failed," said Mycroft. "If only we knew what the coded messages were about. Are they musings on mathematics, or something more sinister? Find the key, Watson, and we'll glimpse Moriarty's mind."
I was intrigued by Dodgson's message. Did he know the key, when even Mycroft Holmes failed? I immediately dispatched a telegram accepting his invitation.
Thus I found myself in Guildford, sipping tea with Charles Dodgson in his parlour. The Reverend, a thin man with uneven blue eyes and sloped shoulders, tilted his left ear towards me as we talked.
"My condolences, Doctor Watson, on the untimely passing of Mr. Holmes," said he. "I fear I must bear some of the burden for his demise."
"Oh? Did you know him?" I asked.
"I knew of Holmes at Oxford, though we never met. It was James Moriarty I knew, through our years at Christ Church debating mathematics and logic. Is there a volume from Moriarty's effects, with a single coded page torn out?"
"Indeed!" I exclaimed. "How did you know?"
"Because I have that page." Dodgson retrieved a copy of Through the Looking Glass from his collection. Tucked within was the coded page he spoke of, folded and yellowed with age. "Tenniel's Jabberwock illustration always reminds me of Moriarty, hypnotic and serpentine."
"How did you get this?"
"That, Doctor, is a twisted tale," said he. "It began with the Order of Copernicus, and ended with the tragic murder of a young prodigy named Arthur Doyle."
The Order of Copernicus is a fellowship of scholars, physicians, mathematicians and philosophers. The Copernicans often invite new members to enrich their symposia with fresh ideas and voices. Moriarty first introduced me to the Order years ago, after he completed his dissertation on the Binomial Theorem. I found their debates enthralling, and participated whenever I could.
In early summer, 1879, Moriarty and I were invited to Aston by a fellow Copernican, Doctor Reginald Hoare. Reginald introduced us to his young lodger, Arthur Doyle, a medical student who was working as a dispensing assistant taking house calls on Reginald's behalf. I found him an engaging conversationalist and a sharp observer.
"What do you plan to do with your future, Arthur?" I asked.
"Surgery, sir," said Arthur. "I'm very much inspired by Doctor Bell at the Edinburgh University. But I'd also like to become a writer like you, actually, and have written some stories for Reginald's children. Edgar Allan Poe's another inspiration, and I'm attempting a mystery now."
"Poe! Now there was a true Copernican. I heard he was a great cryptographer," I said.
Moriarty disagreed. "He indulged in substitution codes, barely worth the effort to solve, unlike Vigenère ciphers."
Arthur asked what a Vigenère cipher was.
"It's based on the Caesar cipher, which shifted letters by a chosen number of positions, looping back to the beginning of the alphabet if necessary," I explained. "Shift the word JABBERWOCKY four positions to the right, you'd have NEFFIVSGOC. To solve the coded message, apply the shift in reverse.
"The Vigenère cipher uses a keyword where each letter in the alphabet represented a different shift. For example, if ALICE were my keyword, that would mean shifts of 0, 11, 8, 2, and 5. The keyword is repeated as needed, and so JABBERWOCKY becomes JLJDIRHWEOY."
Moriarty nodded. "There are mathematical ways to solve a Vigenère code. Kasiski's method determines the length of the keyword by measuring distances between repeating combinations, then uses frequency analysis to break the code. Kerckhoffs' method focuses on solving the keyword itself."
"Moriarty, didn't you have a notebook at Christ Church where you jotted down your formulae?" I asked. "You used a cipher on the annotations. Was that Vigenère?"
Moriarty smiled. "It was, to ensure that the musings and errors of my youth were for my eyes alone. But I'm confident that my code cannot be broken by either the Kerckhoffs or Kasiski solutions. They assume the keyword would be short, and repeated. But if the keyword's significantly long, like a piece of text, then a coded message would be virtually unbreakable."
"Respectfully, Professor, the keyword may be impervious to analysis, but the codemaker is not," said Arthur. "At medical school, Professor Bell taught us to observe the person as well as the disease in our diagnoses. By analyzing the man's habits, experiences and indulgences, one can deduce the choice of text he uses for his code."
"You presume to unriddle my cipher by mere observation?" asked Moriarty.
"If I had the chance to get to know you better, Professor, I daresay I could figure out your code," said Arthur.