"The Gold Bug", Poe on Encryption

Recognized today as the undisputed master of the American Gothic horror story, Edgar Allan Poe (1809–1949) revealed his genius in tales of death, terror, evil, and perversity. Highly skilled in achieving a calculated psychological effect, Poe created chilling fictional nightmares permeated by mysterious forces, grotesque creatures, and improbable hallucinations.

"The Gold-Bug" is a short story by Edgar Allan Poe. Set on Sullivan's Island, South Carolina, the plot follows William Legrand, who was recently bitten by a gold-colored bug. His servant, Jupiter, fears Legrand is going insane and goes to Legrand's friend, an unnamed narrator, who agrees to visit his old friend. Legrand pulls the other two into an adventure after deciphering a secret message that will lead to a buried treasure.

The story involves cryptography with a detailed description of a method for solving a simple substitution cipher using letter frequencies. The cryptogram is:

53‡‡†305))6*;4826)4‡.)4‡);806*;48†8

¶60))85;;]8*;:‡*8†83(88)5*†;46(;88*96

*?;8)*‡(;485);5*†2:*‡(;4956*2(5*—4)8

¶8*;4069285);)6†8)4‡‡;1(‡9;48081;8:8‡

1;48†85;4)485†528806*81(‡9;48;(88;4

(‡?34;48)4‡;161;:188;‡?;

The decoded message is:

A good glass in the bishop's hostel in the devil's seat

twenty-one degrees and thirteen minutes northeast and by north

main branch seventh limb east side shoot from the left eye of the death's-head

a bee line from the tree through the shot fifty feet out.

(The actual decoded message omits spaces and capitalization)

In cryptography, a substitution cipher is a method of encoding by which units of plaintext are replaced with ciphertext, according to a regular system; the "units" may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. The receiver deciphers the text by performing an inverse substitution.

Traditionally, the ciphertext is written out in blocks of fixed length, omitting punctuation and spaces; this is done to help avoid transmission errors and to disguise word boundaries from the plaintext. These blocks are called "groups", and sometimes a "group count" (i.e., the number of groups) is given as an additional check. Five letter groups are traditional, dating from when messages used to be transmitted by telegraph.

Poe played a major role in popularizing cryptograms in newspapers and magazines in his time period and beyond. "The Gold-Bug" also includes the first use of the term "cryptograph" (as opposed to "cryptogram"). To most people in the 19th century, cryptography was mysterious and those able to break the codes were considered gifted with nearly supernatural ability. Poe had drawn attention to it as a novelty over four months in the Philadelphia publication Alexander's Weekly Messenger in 1840. He had asked readers to submit their own substitution ciphers, boasting he could solve all of them with little effort. The challenge brought about, as Poe wrote, "a very lively interest among the numerous readers of the journal. Letters poured in upon the editor from all parts of the country." In July 1841, Poe published "A Few Words on Secret Writing" and, realizing the interest in the topic, wrote "The Gold-Bug" as one of the few pieces of literature to incorporate ciphers as part of the story. Poe's character Legrand's explanation of his ability to solve the cipher is very like Poe's explanation in "A Few Words on Secret Writing". 

William F. Friedman, America's foremost cryptologist, initially became interested in cryptography after reading "The Gold-Bug" as a child—interest he later put to use in deciphering Japan's PURPLE code during World War II.