43 pages • 1 hour read
Simon SinghThe Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography
Nonfiction | Book | Adult | Published in 1999A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Chapters 1-2Chapter Summaries & Analyses
Chapter 1 Summary: The Cipher of Mary Queen of Scots
In 1586, Queen Mary was put on trial for treason, accused of planning to assassinate Queen Elizabeth, Queen of England, in an attempt to take the throne for herself. Her mortal fate hung in the balance and would eventually be decided on the basis of whether or not it could be proved that she was a willing participant in the assassination plot. Those who had already been caught and declared guilty were a party of restless Catholic noblemen intent on bring the nation back to its Catholic roots; this of course necessitated the ousting of the Protestant Elizabeth.
In order to prove that Mary had been involved in the plot, the prosecution needed to show that the ciphers the conspirators had used in their plan, and which they had used in order to communicate with Mary, implicated Mary in the plot explicitly. To do this, the ciphers would have to be interpreted. The judgment of the court depended on this alone, for “if Mary’s cipher was strong enough to conceal her secrets, then there was a chance that she might survive” (18-19).
The use of ciphers in order to conceal messages and important communication dated back to the days of ancient Greece and Rome. In the words of the ancient historian Herodotus, the “art of secret writing” (19) allowed the Greeks to fend off the military advances of the tyrant Xerxes of Persia. The roots of cryptography lie in the most basic act of deception: hiding the message so that it might not fall into enemy hands. Various tactics for this have been employed throughout political and military history and are generally known by the catch-all term steganography, “derived from the Greek words steganos, meaning ‘covered,’ and graphein, meaning ‘to write’” (21). One common example of such a tactic is resorting to various types of invisible ink, where the chemical makeup of the ink used to pen a message allows for it to be hidden and invisible under normal circumstances but easily made manifest by the one to whom it is written. Often, the ink will be made visible by exposing it to some kind of heat source.
In the wake of such simplistic methodology, the manner in which a message was to be hidden evolved. Rather than attempting to hide the message in some way, the actual contents of the message itself became the object of concealment: “Hence, in parallel with the development of steganography, there was the evolution of cryptography, derived from the Greek word kryptos, meaning ‘hidden’” (22). Cryptography involves hiding the meaning of the message rather than the message itself, and thus the first codes and encryptions were born. Cryptography was very quickly recognized as the superior method since even if a message were intercepted, it could not be read thanks to being encrypted in some manner.
In regard to encryption, there are two general paths to take, known as “transposition” or “substitution.” When a message is transposed, the letters or characters of the message are rearranged in some manner. When a message is the subject of a substitution encryption, however, the letters or characters are actually replaced with substitutes, so even the basic units of the words are not present. In both methods, there needs to be a system by which both the sender and receiver determine how the message is to be hidden and then revealed.
One simple example is the railfence transposition, in which the words are written properly but on different lines, alternating back and forth. Transposition codes are typically the most simplistic and therefore the easiest to discover. Substitution codes, however, are more complex and are therefore more desirable from a security standpoint.
Substitution ciphers replace the letters of a written message with other letters on the basis of some previously arranged system. This manner of encryption is also ancient, with one of the oldest examples described by Julius Caesar in his report about the Gallic Wars. In fact, the cipher by which the letters of the alphabet have been replaced by other letters of the same alphabet—thus allowing messages to be written in one’s native alphabet—is typically called a “Caesar shift cipher.” This kind of cipher is capable of being highly simplistic, merely changing the ordering of the alphabet by one letter—A becomes B, B becomes C, etc.—or highly complex, in which the entire alphabet can be shifted and rearranged, allowing for a possible “400,000,000,000,000,000,000,000,000 such rearrangements” (28).
The means by which the plaintext message is transformed into the ciphertext message is called an algorithm: The formula for encrypting the message is applied to each letter or word, and the systematic transformation allows for a repeatable and consistent outcome. When the encrypted message is received, then, the algorithm can be reversed and the original message discovered.
Discovering the meaning of encrypted messages became a science in its own right once the existence of encrypted communication became widespread. In this light, the Babington Plot—the name given to the assassination plot against Queen Elizabeth—becomes rather transparent to the curious investigator.
Chapter 2 Summary: Le Chiffre Indéchiffrable
Ever since its inception, the substitution cipher proved to be more than sufficient for the needs of those who wanted to hide their message from prying eyes. With the discovery of frequency analysis, however, this mode of encryption began to fade out of usefulness. As a result, more complex encryption techniques were developed.
First was an evolution of the substitution cipher, multiplying the cipher alphabets in order to foil basic analysis of this kind. This eventually led to the development of what became known as “Vigenère Square”: an encryption cipher that made use of 26 separate cipher alphabets that allowed for a highly complex mode of concealing a message and completely foiled any attempt at frequency analysis.
In efforts to move away from substitution ciphers, the homophonic cipher was developed, in which not letters but sounds were used, where each letter would be replaced by a variety of options. The best example was known as the Great Cipher and was developed by Antoine and Bonaventure Rossignol, a father-son duo, for use by King Louis XIV. In response to this new cipher, and others as well, the 17th century saw national powers begin to systematize their approaches to breaking codes and ciphers by setting up government bodies to perform the work covertly: “Each European power had its own so-called Black Chamber, a nerve center for deciphering messages and gathering intelligence” (92). The Black Chamber of Austria, located in the capital of Vienna, was the most notorious and capable, even going so far as to sell secrets to other national powers.
In the 18th century, cryptography and espionage entered a new era after the invention of the telegraph. Thanks to this new manner of communication, there was now a need for new forms of communication to similarly be encrypted and kept from discovery (and simultaneously, the need to decipher them as well). While new forms of communication were being invented and implemented, older forms of encryption were being rediscovered and solved. Charles Babbage, for instance, was able to solve the Vigenère cipher, a solution that had been lost for more than a century. While there were no other breakthroughs or invented ciphers or codes over the next century, the 18th and 19th centuries saw a great increase in public interest in the area.
Now that the fast new technology of telegrams was available to the public, people saw the need for private communication due to how telegraphs worked. With letters, the contents were sealed and hidden before leaving the author’s hands. With the telegraph, however, messages needed to be handed off to telegraph operators who needed to read the message in order to relay it: “As people became comfortable with encipherment, they began to express their cryptographic skills in a variety of ways” (118). Cryptography also managed to make its way into popular literature as well, appearing in popular stories by Edgar Allen Poe, Sir Arthur Conan Doyle, and others.
Chapters 1-2 Analysis
Starting the book with one of the most intriguing political plots in history signals the author’s intentions of combining the technical details of code making with historical contexts. The historical reasons for the existence of the codes and ciphers are just as important to the story as the codes themselves and are therefore worthy of attention. In addition, the actual historical events are the reasons that the codes are needed in the first place.
The most essential topic of the first chapter may be in the explanation of frequency analysis, as this will be a topic of importance throughout the remainder of the book. Frequency analysis describes, briefly, an analyst’s assessment of which characters appear most frequently in any given cipher. They attempt to use that statistical information to gain leverage in cracking a code. For example, the letter “E” is the most frequently used letter in the English language, and so a substitution cipher is likely to reflect this in its encoded text. Thus, if one character or encoded letter appears more frequently than any others, there is a good chance that it represents the letter “E.”
When this mode of analysis was discovered, however, the mathematical certainty that frequency analysis offered made simple substitution ciphers all but useless. The Vigenère Square was one such cipher that developed in the wake of most substitution ciphers being solved. The time of this development was one in which the nature of encryption needed to change, and thus the first major development in cryptology occurred. In response to the changing manner of encryption, the world also began to see the establishment of official channels of decryption related to various governments and heads of state. In prior ages, the task of decryption was largely an individually oriented art: Someone with a specific reason to intercept and interpret an encrypted message would attempt to do so; otherwise, there was no widespread and organized system.
With the establishment of various Black Chambers around the world, heads of state saw how useful an officially designated task force would be to focus specifically on methods of espionage and decryption. In the same general time frame, while nations were focused on mechanized methods of decryption, the general public was concerned with finding ways to conceal their private messages with the advent of the telegraph. As with most new technologies, the driving force is always public demand and necessity; with demand for increasingly rapid and efficient means of communication, new technology rose to meet this demand.
However, the telegraph’s manner of operation—which required an expert, officially dedicated operator—necessitated a manner of concealment regarding certain private messages sent between members of the public. Now that everybody had need (theoretically) of certain means of encrypting their messages, the usefulness of such an art became the subject of public fascination. Not surprisingly, this time period—around the age of the Industrial Revolution—also saw a proliferation of popular literature that made use of codes and ciphers in their mysteries and plots. The most famous literary figure to be involved in such an art is probably the detective Sherlock Holmes, a notorious expert in the subject, and around which many mystery stories revolved.
