Wednesday, January 2, 2013

31. Codes



“We have ended by turning the dancing men to good when they have so often been the agents of evil, and I think that I have fulfilled my promise of giving you something unusual for your note-book.”
“The Adventure of the Dancing Men”

“The Adventure of the Dancing Men” introduces the reader to yet another in the arsenal of investigative techniques employed by Sherlock Holmes—cryptanalysis. While the making and breaking of codes has a history dating back to the 9th century Manuscript on Deciphering Cryptographic Messages by Arabic philosopher Abu Al-Kindi, the description in “Dancing Men” of Holmes as code-breaker hearkens to sources already within Conan Doyle’s own set of historical and literary tools. The specific type of analysis Holmes uses is known as frequency analysis, albeit paired with Holmes’s characteristic equal measures of patience and persistence. As chemist Gautam Desiraju explains:

It is a basic rule of cryptology that even the most difficult of codes can be broken if a sufficient number of examples is available. Sherlock Holmes was able to decipher the sinister meaning of the messages in “The Adventure of the Dancing Men,” because he started with the correct assumption that the figures occurring the most often in the bizarre messages corresponded to the letters ‘S’and ‘E’,which occur the most frequently in the English language.

A type of frequency analysis was already familiar to the British public through the highly publicized decipherment of the Rosetta Stone hieroglyphs by Thomas Young and Jean-François Champollion in the 1820’s (by the time of the publication of “Dancing Men,” in 1903, the Stone had been one the British Museum’s most viewed exhibition pieces for over one hundred years). Another type of frequency analysis, conveying a polyphonic rather than polyalphabetic substitution cipher, was also recognizable to readers from Edgar Allen Poe’s 1843 short story “The Gold-Bug,” which popularized code-breaking amongst English and American literary audiences. Though much more complicated to the average citizen but likely familiar to Conan Doyle at the time of writing “Dancing Men,” was the use, by British forces, of the Playfair cipher. Using a third type of substitution, a polygraphic cipher, that resisted attempts at frequency analysis, the code, invented by Charles Wheatstone and promoted by its namesake, Lord Lyon Playfair, was initially rejected by the British, but later adopted during the Second Boer War, where it would may likely have come to Conan Doyle’s attention.

One could surmise that the temptation to elucidate the code-breaking method could come at the expense of the reader, burdening them with technical jargon and long explanations. However, as with many of the forensic advances in the canon, Conan Doyle deftly weaves cryptanalysis into “Dancing Men” without straying too far from the tried-and-true Holmes storytelling. The combination of a seemingly unsolvable cryptographic puzzle and the threat of violent menace that looms over the story combine to make “Dancing Men” easily one of the more suspenseful stories of the canon. 

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