In 1840, Edgar
Allan Poe wrote an article in the Alexander's Weekly
Messenger, a Philadelphia newspaper where he challenged
the readers to submit their own substitution ciphers
which he would decrypt. Initially, he received
cryptograms from around Philadelphia, but soon after,
they came in from all over the United States. He
published many of the cryptograms and their solutions in
fifteen numbers of the Alexander's Weekly Messenger.
The next year, Poe published his essay
called "A Few Words on Secret Writing" in
Graham's Magazine, in which he commented on the response
to his cipher challenge (see download below). The essay
also gave birth to the famous quote that "human
ingenuity cannot concoct a cipher which human ingenuity
cannot resolve".
In the 19th century, most people
considered secret writing and cryptography as a
mysterious esoteric art, and Poe had sparked a great
interest in cryptography among the general public. Thanks
to Poe's publications, cryptogram puzzles became popular
in newspapers and magazines. Inspired by the success of
the cryptograms and the interest in his essay, he decided
to write a short story that involved cryptography.
After writing The Gold-Bug, he
submitted the story to a writing contest, winning the
grand prize and $100. The story was published on June 21,
1843, in Philadelphia's Dollar Newspaper. It is regarded
as the first important publication in popular
non-technical literature that incorporated cryptography
in its story line. The Gold-Bug contains a detailed
description of how to solve a cryptogram using letter
frequency analysis. The story was an instant success and
helped popularize cryptography in the 19th century.
Edgar Allan Poe's The Gold-Bug is as
iconic to cryptography in literature as David Kahn’s
book The Codebreakers is to historical publications on
the subject. It became one of his most read and
best-known stories. Many readers have set their first
steps in cryptology after reading Poe’s story and
some even became important codebreakers, such as the
renowned cryptologist William Friedman. Many writers have
been inspired by Poe to include ciphers and coded
messages in their own books. Poe is also considered one
of the pioneers of detective and mystery stories.
The Story 
The main character in the story is
William Legrand, a man who lives at Sullivan's Island,
near Charleston, South Carolina, to escape from his
misfortunes. Legrand discovers a brilliant gold-colored
bug but lends it out to someone else. When his friend,
the narrator of the story, visits Legrand, he is told
about the rare bug with a death's-head on its back, and
Legrand draws him a picture of the bug on a piece of
paper. A short while later, Legrand asks his friend to
come visit him immediately.
Upon the friend's arrival, the
strangely behaving Legrand asks his friend to follow him
on an expedition into the woods near some rocks, to
search for a treasure. Afraid that Legrand has lost his
mind, the friend decides to accompany him out of concern
for Legrand's health. As it turns out, Legrand
accidentally had discovered a secret message in invisible
writing on the paper he used to draw the bug. Legrand
later explains his friend how he found the message and
how he was able to decrypt the message that started his
quest for a hidden treasure.
The cryptogram, as discovered by
Legrand:
You can download a printable
version in txt format.
The Gold-Bug is not only an exciting
story about the discovery of an old treasure, but also a
great introduction to cryptography and codebreaking. It
tickles the reader's curiosity and Poe gives a detailed
description of how to decipher the cryptogram. While
doing so, he also provides the solution. However,
deciphering the message yourself is even more exciting
than reading how Legrand did it in the story. Can I
challenge you, just as Poe did, to decrypt Legrand’s
message, composed more than 160 years ago?
Decrypting the Message
Rather than just reading Poe’s
story, I will show you the technique and give you the
chance to do it all by yourself. It might be useful to
read The Gold-Bug first, as
the story might provide information that will help to
solve the cryptogram but read only to where the
cryptogram appears. Don't cheat by reading or
peeking any further! Don't search the Internet for Poe or
The Gold-Bug, as this will also spoil the fun.
The message is encrypted by
mono-alphabetic substitution, a cipher where each letter
of the alphabet is replaced by other symbol or letter. We
can calculate all possible combinations for the 26
letters of the alphabet. The first letter is substituted
by one of 26 symbols or letters, including itself. The
second by one of the 25 remaining symbols or letters, and
so on. The calculation 26 x 25 x 24…x3 x2 x 1 or 26!
gives us a total of 403,291,461,126,605,635,584,000,000
different ways to replace 26 letters by another symbol or
letter. How on earth could we possibly decipher such a
cryptogram? For centuries, substitution ciphers were
regarded as unbreakable...but it is easier than it looks.
Although there are trillions of ways to
allocate a set of symbols to letters, there are only a
few ways to combine vowels and consonants in a natural
language. Strict linguistic rules determine which letter
combinations are possible and which are not. The syntax
prescribes how words, and their order, are combined into
a sentence, and conjugation rules determine how verbs are
written. When we substitute letters with symbols, those
symbols still follow all these rules and therefore create
patterns that we can detect. Just as certain letter
combinations are impossible (ZLG, XOJ, KFN,...), so will
certain symbols avoid one another. Just as one vowel can
only fit in a given set of consonants (THR?ST, L?GHT,
?NSW?R,...) so will certain symbols attract each other.
But where do we start?
The mystery weapon to solve our message
is letter frequency analysis, the basis of all
codebreaking. Each language has its own typical
distribution of letters in a text. In English, the letter
e is by far the dominant letter, with an average of 12.7
percent. If we locate some of the most frequent vowels or
consonants in the ciphertext, or find recurring symbol
combinations, then the rules of the language will give us
strong leads to the words they are used in, or the letter
they represent. Below, you'll find the letters of the
alphabet, ordered from most frequent at the left to least
frequent at the right (Poe used an older and slightly
different frequency table).
E T A O I N S R H L D C U M F P
G W Y B V K X J Q Z
For Legrand’s message, start by
taking a sheet with squares and write down the secret
message with a pen. Leave some blank rows between each
row of the message, to write your solution underneath the
symbols with a pencil (easily corrected with a gum).
Count how many times each of the symbols appears in the
cryptogram and write down the results in a table, ordered
from most to least frequent. You will see that one of the
symbols clearly stands out. This is the first major clue.
That most frequent symbol represents without doubt the
most frequent letter of the alphabet. Write your first
results underneath the according symbols on your message
sheet.
Next, you try to spot recurring
combinations of symbols. The most used words in English,
in order of frequency, are THE, OF, AND, TO and IN.
Therefore, you must search for identical combinations of
symbols that contain the most frequent letter you already
found. You should spot each THE quite easily. If so, you
have discovered the solution for two more letters that
are used frequently. Make yourself a second table with
all the symbols and their corresponding letters you
already found.
By now, you should be able to find more
and more letters by completing fragments. If, for
instance, you find a fragment T?EE, it is not hard to
imagine what should follow the letter T. Vowels twins
(AA, EE, OO…) are common but not that many different
words contain such pairs. Try to find those words. If you
can’t see it immediately, try all letters of the
alphabet until you get something readable. Each new
letter will help you to reconstruct more and more
fragments. Be patient. It could take some time before a
word appears in front of you, but once you have four or
five letters, you’re in a straight line to the
finish.
Good luck...and make sure you don't get
bitten by the bug!
Note: in the original edition, one
symbol "(" was not printed near the end of the
message, right after ‡9;48; although Legrand
describes just that missing symbol to assist in finding a
word. Since the story refers to that symbol, it is
unlikely that it was omitted on purpose and probably got
lost during the publishing.
Downloads
More on Manual Ciphers
- Hand Ciphers
Various techniques to encrypt messages with pen
and paper.
More About Poe (offsite, opens in new
tab)
