The Philosophical Breakfast Club (56 page)

In Bacon’s time, diplomats routinely sent messages in cipher; learning the art of encryption was part of the training of future statesmen. Bacon himself was well versed in the art; his brother Anthony, known to be a British spy working in France, often passed letters to Francis, sometimes in cipher, and many believe that Francis too worked as a secret agent at times, sending his own encrypted messages.
¹⁰
In his work
De Augmentis
, the Latin translation of a longer version of his
Advancement of Learning
, Bacon wrote on the importance of ciphers, and invented one of his own, in which each letter of the plain text is replaced by some combination of five a’s and b’s. Bacon’s interest in ciphers would later spawn an entire industry of conspiracy theorists convinced that Bacon was the author of the works attributed to William Shakespeare, and that he had “encrypted” those works with his secret story as the illegitimate son and heir of Queen Elizabeth I, only nominally the “Virgin Queen.”
¹¹

In the late 1830s, public interest in ciphers was revitalized by a new invention: the electric telegraph, which transmitted electric signals over
wires, enabling speedy long-distance communication for the first time. In 1837, Babbage’s friend Charles Wheatstone—who, like Babbage, was obsessed with ciphers and codes—joined with another physicist, William Cooke, to invent the first electric telegraph in Great Britain. Their system built upon the discovery of the Danish physicist Hans Christian Oersted that electric current in a wire generates a magnetic field that can deflect a compass needle. The Cooke-Wheatstone telegraph used this principle, as well as the later invention of the electromagnet, to send signals through a wire resulting in motions of one or more needles that could be translated into alphabetical symbols, spelling out the message. By the early 1840s the Cooke-Wheatstone telegraph had been installed at numerous stations of Isambard Kingdom Brunel’s Great Western Railway.

At around the same time, in the United States, Samuel Morse was developing his own system of electric telegraphy, in which a series of short and long elements, known as dots and dashes, were used as a substitute alphabet; these dots and dashes could be transmitted over wires via electrical impulses. Eventually the Morse telegraph would take over in Europe, even in England, where it displaced the Cooke-Wheatstone model.

Morse code was not a cipher, in the sense that it did not encrypt a message that was safe from being understood by others. Rather, it was an alternative alphabet, one made up of dots and dashes. To send a message by telegraph required giving it to the telegraph operator, who would read it and translate it into the Morse alphabet. The message’s meaning would be clear to the operator sending it, as well as to the operator on the receiving end, and to anyone who happened to intercept the message who could read Morse code. This was worrisome to people sending secret business communications or very personal information. A newspaper article of the time on telegraphy lamented “the violation of all secrecy” felt by those who sent telegrams, and called for the development of a “simple yet secure cipher” that would enable coded messages to be sent and received, but not understood by the operators.
¹²
People began to experiment with constructing ciphers that could be used for this purpose. Wheatstone would go on to invent a cipher that became known as “Playfair’s cipher,” because his friend Lyon Playfair lobbied loudly for its adoption by the War Office.
¹³

Interest in cryptology extended even to everyday life. Young lovers, forbidden to express their affections publicly, and often even prohibited from meeting, were afraid to send letters that could be intercepted
by their parents. Instead, they corresponded by placing encrypted messages in the personal columns of newspapers, called “agony columns.” Babbage, Wheatstone, and Playfair liked to get together and scan the columns, trying to decipher the contents, which were often risqué. One time, Wheatstone deciphered a message from a young man, studying at Oxford, begging his young lover to run off with him to Gretna Green, the village just over the border of Scotland famous for hosting the “runaway marriages” of parties under twenty-one years old without parental consent (which was required in England). Wheatstone playfully placed his own message in the next day’s column, written in the same cipher, counseling the couple against taking this rash and irrevocable step. The next edition of the paper contained a message from the young lady, this time unencrypted: “Dear Charlie, write no more. Our cipher is discovered!”
¹⁴
The three men had a good chuckle, and Babbage saved the clippings for his growing collection of newspaper ciphers.

Babbage’s interest in codes and ciphers was born during his schoolboy days; it appealed to his desire to get to the essence and hidden meanings of things, demonstrated even in his infanthood when he would break his toys to find out what was inside. When he was at school, Babbage’s skill at decoding would often get him into trouble: “The bigger boys made ciphers, but if I got hold of a few words, I usually found out the key,” he boasted. “The consequence of this ingenuity was occasionally painful: the owners of the detected ciphers sometimes thrashed me, though the fault lay in their own stupidity.”
¹⁵
Black eyes and bruised knuckles notwithstanding, Babbage gained the lifelong belief that “deciphering is, in my opinion, one of the most fascinating of arts.”

Like Babbage, Herschel was a schoolboy enamored of decoding. Herschel’s first known letter was sent to his mother from his school when he was seven years old requesting that she send his music and his “ciphering books.”
¹⁶
Whewell was also drawn to codes and ciphers as a young man. His youthful courtship of a girl was abetted by a cipher; upon the young woman’s request, Whewell wrote a bit of doggerel in an elementary cipher, replacing the word “cipher/sigh for” with the symbol “Ø”:

(You sigh for a cipher, but I sigh for you; O sigh for no cipher but O sigh for me; O let not my sigh for a cipher go, But give sigh for a sigh, for I sigh for you so.)
¹⁷
It is not known whether or not the cipher had the intended effect on the young lady.

It is little wonder that the members of the Philosophical Breakfast Club were all intrigued by ciphers. Deciphering is like scientific discovery—confronting an initially impenetrable wall, the cryptanalyst, like the scientist, must slowly chip away until the secrets that lie beneath are revealed. Both Whewell and Herschel explicitly drew this connection in their writings on scientific method, describing scientific discovery as a kind of decoding of nature. Whewell used this metaphor when he argued for the importance of predictive success, noting that such success is evidence that we have cracked nature’s code. And he came to hold that the world of facts is like an alphabet used to encrypt a secret message; when natural philosophers “had deciphered there a comprehensive and substantial truth, they could not believe that the letters had been thrown together by chance.”
¹⁸
In an article written for the fledgling journal
Photographic News
, Herschel similarly proposed that finding a method for creating color photographs (which he had very nearly managed to do himself) was akin to breaking a seemingly impenetrable cipher; Herschel appended to the article a text written in a cipher of his own, leaving it for the readers to try to decode the message.
¹⁹
He had previously tried to stump Babbage, sending him a letter written entirely in cipher (except for “Dear Babbage”). Babbage broke the cipher handily, leading Herschel to exclaim, “You are a
real wonder.…
I shall never try to trick you again!”
²⁰

B
ABBAGE HAD RETURNED
to his childhood interest in ciphers during the 1830s. In 1835, Babbage employed his considerable skills in cryptanalysis to aid his friend and fellow founder of the Astronomical Society, Francis Baily, who was writing a book on John Flamsteed (1646–1719), the first Astronomer Royal. Baily was attempting to establish the accuracy of Flamsteed’s observations from the Royal Observatory at Greenwich, and the cause for some known errors in those observations. In his writings, Flamsteed had suggested that the problems were due to an error in his mural arc, the angle-measuring device built right into a wall lying on the prime meridian at Greenwich, marking the point of zero longitude. If the mural arc was responsible for the errors, the fault would lie with its builder, not
with Flamsteed himself. Baily found a letter from Abraham Sharp, Flamsteed’s assistant, written in response to a query from a Mr. Crosthwait about whether such an error existed. Sharp’s letter, however, was written in a cipher, so Baily was unable to learn its contents. He mentioned the problem to Babbage, who, “by a laborious and minute examination and comparison of all the parts,” Baily later explained, was able to decipher the letter. This enabled Baily to discover that the errors arose not from the mural arc, as Flamsteed had rather deceptively implied, but from the refraction table he had used.
²¹
Thanks to Babbage, Baily was able to solve a problem about Flamsteed’s observations that had haunted astronomers for over a century. It also influenced later astronomers’ opinions of the first Astronomer Royal; Herschel told Beaufort that reading Baily’s book had diminished his opinion of Flamsteed as a person and an astronomer.
²²

At around this time—just when Babbage was most involved with the newly founded Statistical Society of London, and the Statistical Section of the British Association—he began to apply statistics to the problem of deciphering, nearly a century before William F. Friedman, who is generally considered the first to have done so.
²³
In a letter to Quetelet, which the Belgian translated and had published in a French journal, Babbage listed tables of the relative frequencies of double letters in English, French, Italian, German, and Latin. In English, it turns out, the most frequently doubled letter is l, which occurs 27.8 times in 10,000 letters (16.1 times in the middle of a word, 11.7 times at the end). The next most frequently doubled letter is
e
, 18.8 times in the middle of a word, and 1.9 times at the end. The rarest doubled letter is
g
, which is found only 1.5 times in 10,000 letters.
²⁴

Babbage also began to count the relative frequency of the occurrence of single letters, and made lists of the most common two- and three-letter words, organizing them by their consonant/vowel pattern, such as CCV, VCC, CVC, VCV, CVV, VVC, and VVV. Then he began to order words that end in
-ion
according to word length.
²⁵
He started writing dictionaries of words that began with each of the twenty-six letters of the alphabet, ordered by how many letters were in each word. All of this was to be part of a planned book, called
The Philosophy of Decyphering
, but Babbage never actually wrote it.

Babbage had realized that these kinds of statistical studies would be invaluable in deciphering any monoalphabetic cipher. In a monoalphabetic cipher, letters in the plain text are substituted by letters in an alphabet
defined differently from the standard ordered alphabet. This cipher alphabet can be shifted (e.g., instead of “a,b,c,d” you might have “b,c,d,e” or “c,d,e,f”), inverted (“z,y,x,w”), or ordered by the use of a key word or phrase, in which case the cipher alphabet begins with the key word and then continues with the rest of the alphabet, in order but minus the letters already appearing in the key word (e.g., key word “leopard”: l,e,o,p,a,r,d,b,c,f,g,h,i,j,k,m,n,q,s,t,u,v,w,x,y,z).

In order to encrypt a message using this cipher alphabet, the writer would place the normal alphabet over the cipher alphabet, and replace each letter in the plain text with the matching letter in the cipher alphabet.

So, “attack the enemy fortress” becomes “lttlog tba ajapy rcftfass.” To make the deciphering more difficult, the spaces could be omitted, and the cipher text would read “lttlogtbaajapyrcftfass.” The person sent the cipher text would have been provided with the key word, and would use the opposite procedure to decipher the message.

In a monoalphabetic cipher, the cipher alphabet is fixed for the entire encryption.
²⁶
Babbage’s study of letter frequency, especially of the double letters, provides an important and effective method for cryptanalysis. Since we know that the letter
l
is the most frequently doubled letter, we can begin deciphering a text by substituting
l
for all the cases of double letters. Similarly, Babbage’s list of the consonant/vowel patterns of two- and three-letter words can also help in finding a way into an encrypted message, by seeking those patterns in the cipher text. Further, his study of letter frequency is useful because the most common letters,
e, t
, and
a
, will generally stand out, however they are disguised, since they are substituted with the same letter each time. So, in the example above, since the letter
a
appears the most frequently, the cryptanalyst can start by assuming that
a
is the substitution for
e, t
, or
a
(in fact, it is the substitution for
e
). It was by applying methods such as this that Babbage was able to decipher the Childe letters; his first breakthrough came when he realized that the most common word in the cipher text was “sqj,” which he soon determined stood for the common plain-text word “the.” By replacing all the occurrences of
s
with
t, q
with
h
, and
j
with
e
, Babbage was able to start breaking down the wall.