Simon Singh received his Ph.D. in physics from Cambridge University. A former BBC producer, he directed and
co-produced an award-winning documentary film on Fermat's Last Theorem that aired on PBS's Nova series and formed
the basis of his bestselling book, Fermat's Enigma. He lives in London.
Sample Chapter
EXCERPT
On the morning of Wednesday, 15 October 1586, Queen Mary entered the crowded courtroom at Fotheringhay Castle.
Years of imprisonment and the onset of rheumatism had taken their toll, yet she remained dignified, composed and
indisputably regal. Assisted by her physician, she made her way past the judges, officials and spectators, and
approached the throne that stood halfway along the long, narrow chamber. Mary had assumed that the throne was a
gesture of respect towards her, but she was mistaken. The throne symbolised the absent Queen Elizabeth, Mary's
enemy and prosecutor. Mary was gently guided away from the throne and towards the opposite side of the room, to
the defendant's seat, a crimson velvet chair.
Mary Queen of Scots was on trial for treason. She had been accused of plotting to assassinate Queen Elizabeth in
order to take the English crown for herself. Sir Francis Walsingham, Elizabeth's Principal Secretary, had already
arrested the other conspirators, extracted confessions, and executed them. Now he planned to prove that Mary was
at the heart of the plot, and was therefore equally culpable and equally deserving of death.
Walsingham knew that before he could have Mary executed, he would have to convince Queen Elizabeth of her guilt.
Although Elizabeth despised Mary, she had several reasons for being reluctant to see her put to death. First, Mary
was a Scottish queen, and many questioned whether an English court had the authority to execute a foreign head
of state. Second, executing Mary might establish an awkward precedent -- if the state is allowed to kill one queen,
then perhaps rebels might have fewer reservations about killing another, namely Elizabeth. Third, Elizabeth and
Mary were cousins, and their blood tie made Elizabeth all the more squeamish about ordering her execution. In short,
Elizabeth would sanction Mary's execution only if Walsingham could prove beyond any hint of doubt that she had
been part of the assassination plot.
The conspirators were a group of young English Catholic noblemen intent on removing Elizabeth, a Protestant, and
replacing her with Mary, a fellow Catholic. It was apparent to the court that Mary was a figurehead for the conspirators,
but it was not clear that she had actually given her blessing to the conspiracy. In fact, Mary had authorised the
plot. The challenge for Walsingham was to demonstrate a palpable link between Mary and the plotters.
On the morning of her trial, Mary sat alone in the dock, dressed in sorrowful black velvet. In cases of treason,
the accused was forbidden counsel and was not permitted to call witnesses. Mary was not even allowed secretaries
to help her prepare her case. However, her plight was not hopeless because she had been careful to ensure that
all her correspondence with the conspirators had been written in cipher. The cipher turned her words into a meaningless
series of symbols, and Mary believed that even if Walsingham had captured the letters, then he could have no idea
of the meaning of the words within them. If their contents were a mystery, then the letters could not be used as
evidence against her. However, this all depended on the assumption that her cipher had not been broken.
Unfortunately for Mary, Walsingham was not merely Principal Secretary, he was also England's spymaster. He had
intercepted Mary's letters to the plotters, and he knew exactly who might be capable of deciphering them. Thomas
Phelippes was the nation's foremost expert on breaking codes, and for years he had been deciphering the messages
of those who plotted against Queen Elizabeth, thereby providing the evidence needed to condemn them. If he could
decipher the incriminating letters between Mary and the conspirators, then her death would be inevitable. On the
other hand, if Mary's cipher was strong enough to conceal her secrets, then there was a chance that she might survive.
Not for the first time, a life hung on the strength of a cipher.
The Evolution of Secret Writing
Some of the earliest accounts of secret writing date back to Herodotus, 'the father of history' according to the
Roman philosopher and statesman Cicero. In The Histories, Herodotus chronicled the conflicts between Greece and
Persia in the fifth century bc, which he viewed as a confrontation between freedom and slavery, between the independent
Greek states and the oppressive Persians. According to Herodotus, it was the art of secret writing that saved Greece
from being conquered by Xerxes, King of Kings, the despotic leader of the Persians.
The long-running feud between Greece and Persia reached a crisis soon after Xerxes began constructing a city at
Persepolis, the new capital for his kingdom. Tributes and gifts arrived from all over the empire and neighbouring
states, with the notable exceptions of Athens and Sparta. Determined to avenge this insolence, Xerxes began mobilising
a force, declaring that 'we shall extend the empire of Persia such that its boundaries will be God's own sky, so
the sun will not look down upon any land beyond the boundaries of what is our own'. He spent the next five years
secretly assembling the greatest fighting force in history, and then, in 480 bc, he was ready to launch a surprise
attack.
However, the Persian military build-up had been witnessed by Demaratus, a Greek who had been expelled from his
homeland and who lived in the Persian city of Susa. Despite being exiled he still felt some loyalty to Greece,
so he decided to send a message to warn the Spartans of Xerxes' invasion plan. The challenge was how to dispatch
the message without it being intercepted by the Persian guards. Herodotus wrote:
As the danger of discovery was great, there was only one way in which he could contrive to get the message through:
this was by scraping the wax off a pair of wooden folding tablets, writing on the wood underneath what Xerxes intended
to do, and then covering the message over with wax again. In this way the tablets, being apparently blank, would
cause no trouble with the guards along the road. When the message reached its destination, no one was able to guess
the secret, until, as I understand, Cleomenes' daughter Gorgo, who was the wife of Leonides, divined and told the
others that if they scraped the wax off, they would find something written on the wood underneath. This was done;
the message was revealed and read, and afterwards passed on to the other Greeks.
As a result of this warning, the hitherto defenceless Greeks began to arm themselves. Profits from the state-owned
silver mines, which were usually shared among the citizens, were instead diverted to the navy for the construction
of two hundred warships.
Xerxes had lost the vital element of surprise and, on 23 September 480 bc, when the Persian fleet approached the
Bay of Salamis near Athens, the Greeks were prepared. Although Xerxes believed he had trapped the Greek navy, the
Greeks were deliberately enticing the Persian ships to enter the bay. The Greeks knew that their ships, smaller
and fewer in number, would have been destroyed in the open sea, but they realised that within the confines of the
bay they might outmanoeuvre the Persians. As the wind changed direction the Persians found themselves being blown
into the bay, forced into an engagement on Greek terms. The Persian princess Artemisia became surrounded on three
sides and attempted to head back out to sea, only to ram one of her own ships. Panic ensued, more Persian ships
collided and the Greeks launched a full-blooded onslaught. Within a day, the formidable forces of Persia had been
humbled.
Demaratus' strategy for secret communication relied on simply hiding the message. Herodotus also recounted another
incident in which concealment was sufficient to secure the safe passage of a message. He chronicled the story of
Histaiaeus, who wanted to encourage Aristagoras of Miletus to revolt against the Persian king. To convey his instructions
securely, Histaiaeus shaved the head of his messenger, wrote the message on his scalp, and then waited for the
hair to regrow. This was clearly a period of history that tolerated a certain lack of urgency. The messenger, apparently
carrying nothing contentious, could travel without being harassed. Upon arriving at his destination he then shaved
his head and pointed it at the intended recipient.
Secret communication achieved by hiding the existence of a message is known as steganography, derived from the
Greek words steganos, meaning 'covered', and graphein, meaning 'to write'. In the two thousand years since Herodotus,
various forms of steganography have been used throughout the world. For example, the ancient Chinese wrote messages
on fine silk, which was then scrunched into a tiny ball and covered in wax. The messenger would then swallow the
ball of wax. In the fifteenth century, the Italian scientist Giovanni Porta described how to conceal a message
within a hard-boiled egg by making an ink from a mixture of one ounce of alum and a pint of vinegar, and then using
it to write on the shell. The solution penetrates the porous shell, and leaves a message on the surface of the
hardened egg albumen, which can be read only when the shell is removed. Steganography also includes the practice
of writing in invisible ink. As far back as the first century ad, Pliny the Elder explained how the 'milk' of the
thithymallus plant could be used as an invisible ink. Although transparent after drying, gentle heating chars the
ink and turns it brown. Many organic fluids behave in a similar way, because they are rich in carbon and therefore
char easily. Indeed, it is not unknown for modern spies who have run out of standard-issue invisible ink to improvise
by using their own urine.
The longevity of steganography illustrates that it certainly offers a modicum of security, but it suffers from
a fundamental weakness. If the messenger is searched and the message is discovered, then the contents of the secret
communication are revealed at once. Interception of the message immediately compromises all security. A thorough
guard might routinely search any person crossing a border, scraping any wax tablets, heating blank sheets of paper,
shelling boiled eggs, shaving people's heads, and so on, and inevitably there will be occasions when the message
is uncovered.
Hence, in parallel with the development of steganography, there was the evolution of cryptography, derived from
the Greek word kryptos, meaning 'hidden'. The aim of cryptography is not to hide the existence of a message, but
rather to hide its meaning, a process known as encryption. To render a message unintelligible, it is scrambled
according to a particular protocol which is agreed beforehand between the sender and the intended recipient. Thus
the recipient can reverse the scrambling protocol and make the message comprehensible. The advantage of cryptography
is that if the enemy intercepts an encrypted message, then the message is unreadable. Without knowing the scrambling
protocol, the enemy should find it difficult, if not impossible, to recreate the original message from the encrypted
text.
Although cryptography and steganography are independent, it is possible to both scramble and hide a message to
maximise security. For example, the microdot is a form of steganography that became popular during the Second World
War. German agents in Latin America would photographically shrink a page of text down to a dot less than 1 millimetre
in diameter, and then hide this microdot on top of a full stop in an apparently innocuous letter. The first microdot
to be spotted by the FBI was in 1941, following a tip-off that the Americans should look for a tiny gleam from
the surface of a letter, indicative of smooth film. Thereafter, the Americans could read the contents of most intercepted
microdots, except when the German agents had taken the extra precaution of scrambling their message before reducing
it. In such cases of cryptography combined with steganography, the Americans were sometimes able to intercept and
block communications, but they were prevented from gaining any new information about German spying activity. Of
the two branches of secret communication, cryptography is the more powerful because of this ability to prevent
information from falling into enemy hands.
In turn, cryptography itself can be divided into two branches, known as transposition and substitution. In transposition,
the letters of the message are simply rearranged, effectively generating an anagram. For very short messages, such
as a single word, this method is relatively insecure because there are only a limited number of ways of rearranging
a handful of letters. For example, three letters can be arranged in only six different ways, e.g. cow, cwo, ocw,
owc, wco, woc. However, as the number of letters gradually increases, the number of possible arrangements rapidly
explodes, making it impossible to get back to the original message unless the exact scrambling process is known.
For example, consider this short sentence. It contains just 35 letters, and yet there are more than 50,000,000,000,000,000,000,000,000,000,000
distinct arrangements of them. If one person could check one arrangement per second, and if all the people in the
world worked night and day, it would still take more than a thousand times the lifetime of the universe to check
all the arrangements.
"It would be hard to imagine a clearer or more fascinating presentation. . . . Mr. Singh gives cryptography
not only its historical dimension but its human one."
--The New York Times
"Entertaining and satisfying. . . . Offers a fascinating glimpse into the mostly secret competition between
codemakers and codebreakers."
--USA Today
"A good read that, bless it, makes the reader feel a bit smarter when it's done. Singh's an elegant writer
and well-suited to the task of leading the mathematically perplexed through areas designed to be tricky."
--Seattle Weekly
"An absorbing tale of codemaking and codebreaking over the centuries."
--Scientific American
"Singh spins tales of cryptic intrigue in every chapter."
--The Wall Street Journal
"Brings together...the geniuses who have secured communications, saved lives, and influenced the fate of nations.
A pleasure to read."
--Chicago Tribune
"Enthralling...commendably lucid...[Singh's] book provides a timely and entertaining summary of the subject."
--The Economist
Random House, Inc. Web Site, April, 2002
Summary
In his first book since the bestselling Fermat's Enigma, Simon Singh offers the first sweeping history of encryption,
tracing its evolution and revealing the dramatic effects codes have had on wars, nations, and individual lives.
From Mary, Queen of Scots, trapped by her own code, to the Navajo Code Talkers who helped the Allies win World
War II, to the incredible (and incredibly simple) logisitical breakthrough that made Internet commerce secure,
The Code Book tells the story of the most powerful intellectual weapon ever known: secrecy.
Throughout the text are clear technical and mathematical explanations, and portraits of the remarkable personalities
who wrote and broke the world's most difficult codes. Accessible, compelling, and remarkably far-reaching, this
book will forever alter your view of history and what drives it. It will also make yo wonder how private that e-mail
you just sent really is.