My middle school years were spent in an English-medium school in
India. Among our assigned literature readings was a short story by
Edgar Allan Poe named "The Gold-Bug." This story introduced me to
cryptography, the science of secret messages.
Every time you swipe your credit card to buy something, or log into
your bank account, you're using cryptography. Modern life is built on
top of certain major advances in this field since World War II, and
Edgar Allan Poe's story played a role in inspiring the people who made
them.
The Gold-Bug is not much of a story, as far as plot and character
go. While collecting a rare beetle on a beach, a white man and his
black manservant discover an old parchment paper with a message
written in strange symbols, some sort of secret code.
The story spends most of its pages explaining how the man cracks the
code to discover where a pirate's treasure is buried. Still, it's got
enough atmosphere of mystery with a hint of the macabre, with
disappearing ink, skulls nailed on trees, and a good body count, to
hook a young person.
At the time, I had no idea who Edgar Allan Poe was, and how old this
story was. But since coming to Boston, where he was born and where the
city has a statue of him on Boylston Street, I've learned more about
the tortured writer's life and his obsessions. His 215th birthday
would have been last week.
It was around 1840 that Poe's fascination with logic and reasoning led
him to study the encoding of information. In those days, most people
thought of the art of writing secret messages as a kind of occult
magic. Poe, however, ever the rationalist, dismissed such
fancies. Anyone could write and break secret messages via logical
reasoning.
He wrote "The Gold-Bug" as an introduction to the topic, then
submitted it to a Philadelphia newspaper's writing contest and won a
hundred dollars for it. The paper published it in 1843. It's probably
the oldest piece of fiction to incorporate cryptography, and certainly
the first to use the term.
The Puzzle
The secret message in the story is an example of a simple
substitution cipher, where each letter in a piece of text is
replaced by some number or symbol. To read the message, you need a
key, a table that shows which symbol stands for which letter.
These substitution ciphers can be decoded without a key by
systematically applying logical reasoning and exploring different
possibilities.
Assuming the message is in English, you start with a table of how
frequently various letters, sequences of letters, and words appear in
typical English-language text: *e* is the most frequent letter,
followed by taoinshrdl and so on. In the story, the protagonist
counts the frequencies of the symbols on the parchment and writes out
an entire table: 8 is the most frequent character,
semicolon is the next most frequent, then 4, and so on.
This analysis gives you a place to start. Perhaps 8 stands for *e*,
semicolon stands for *t*, etc. You try these substitutions to see if
the message spells out English words, and if you see mistakes, you can
change them until you have figured out the key.
This kind of analysis is similar to the mathematical models needed to
generate text, as I discussed in an earlier blog
post about generative text models
like ChatGPT. Claude Shannon, who laid the foundations of information
theory after World War II, once told an interviewer that he had read
The Gold-Bug as a child.
Addendum
When I first read this story in middle school, I used the cipher
devised by the protagonist to uncover the secret message. But the
resulting message was not correct: it produced the word "fosty"
instead of "forty."
The story as published in various outlets has different mistakes in
the typography of the parchment paper. I have seen at least three
different versions with different mistakes.
The version in the picture above is the scan in the Gutenberg website.
It has the same mistake as the one I read, producing the word "fosty"
in the resulting message. But it couldn't have been Poe's fault. By
the time he wrote The Gold-Bug, Poe had done a pretty thorough
analysis of hundreds of messages submitted by his readers in response
to his essays on cryptography in another magazine.
Fortunately, we now have the original version of the story
painstakingly scanned and proof-read by The Edgar Allan Poe Society of
Baltimore on their
website. They have
scanned The Gold-Bug from the original Dollar Newspaper, where it
appears without any mistakes:
5 3 ‡ ‡ † 3 0 5 ) ) 6 * ; 4 8 2 6 ) 4 ‡
. ) 4 ‡ ) ; 8 0 6 * ; 4 8 † 8 ¶ 6
0 ) ) 8 5 ; 1 ‡ ( ; : ‡ * 8 † 8
3 ( 8 8 ) 5 * † ; 4 6 ( ; 8 8 * 9 6 * ? ; 8 )
* ‡ ( ; 4 8 5 ) ; 5 * † 2 : * ‡
( ; 4 9 5 6 * 2 ( 5 * — 4 ) 8 ¶ 8 * ; 4 0
6 9 2 8 5 ) ; ) 6 † 8 ) 4 ‡ ‡ ;
1 ( ‡ 9 ; 4 8 0 8 1 ; 8 : 8 ‡ 1 ; 4 8
† 8 5 ; 4 ) 4 8 5 † 5 2 8 8 0 6 * 8 1 (
‡ 9 ; 4 8 ; ( 8 8 ; 4 ( ‡ ? 3 4 ; 4 8 )
4 ‡ ; 1 6 1 ; : 1 8 8 ; ‡ ? ;
Enjoy!