Encryption, which derives from the Greek word “kriptos,” refers to the concealment of information through the conversion of plain text into ciphered or encoded text. So pervasive is this ancient expression of secrecy that encryption might be read as the physical manifestation of conspiracy in language.

From the court conspiracies of the Middle Ages to the world of cold war espionage, countless conspiracies and conspiracy theories have been based on the encoding or decoding of encrypted messages. The earliest example of encryption can be traced back to 1,900 B.C. when unconventional hieroglyphics were found on the tomb of Khumhotop II in the place of more standard inscriptions.

While their intent was not to make the message secret, but rather to obscure its meaning and thus attract the attention of passersby, it nevertheless stands as one of the first known examples of codemaking.

The Kama Sutra of Vatsyayana catalogs encryption (or, “secret writing” and “secret talking”) as the forty-fourth and forty-fifth of the sixty-four arts, along with others such as meditation, cooking, and bookbinding. Other examples include cuneiform tablets in ancient Mesopotamia and the atbash cipher of the Old Testament. Yet it was not until the mid-ninth century that cryptography developed into an actual science.

Arab scholars produced influential treatises and studies of the subject, and invented the equally important discipline of cryptanalysis (the decipherment of encrypted messages) primarily through methods of frequency analysis. This legacy can still be identified in the word “cipher,” which originates from the Arabic sifr, or “zero.”

One of the earliest and simplest methods of encryption is the substitution cipher. This system is credited to Julius Caesar and employs an alphabet in which plaintext letters are replaced by the third letter that follows in the alphabet; thus A becomes D, B become E, and so on.

The closely related transposition method involves the rearrangement of plaintext letters in a word or a sentence, creating a kind of anagram. More often, the transposition method relies on a preestablished key possessed by both the sender and receiver of the message, such as a parallel list of plaintext and ciphertext alphabets.

Closely allied to encryption, and often used in conjunction with it, is the practice of steganography (from the Greek word for “covered writing”). Steganography, which according to Herodotus is at least as old as 440 B.C., refers to the secret transmission of a message.

In classical times this might mean using invisible inks, such as milk or urine, or even going as far as tattooing a message on the head of a slave and allowing his or her hair to grow back. In modern times, messages have been photographed and reduced to the size of microdots, electronically embedded in image files, and placed in plain view on the Internet.

Since its beginnings, encryption has emerged as one of the fundamental necessities of statecraft. Its use in political affairs became well established in the Western world in the seventeenth century when black chambers were established by nations across Europe.

The black chambers, such as France’s Cabinet Noir and Vienna’s Geheime Kabinets-Kanzlei, operated as secret rooms where messages between diplomats and other government personnel were intercepted and cryptanalyzed, before proceeding through the postal service to their addressees.

In France, Cardinal Richelieu recognized the value of decrypting the messages of foreign powers, and with the help of Antoine Rossignol (and later his son, Bonaventure), began developing new methods of cryptanalysis, even inventing the Great Cipher (“le chiffre indéchiffrable”) of Louis XIV.

Encryption has proved no less important in the twentieth century, having had far-reaching effects in both the Machiavellian intrigues of political life and in wartime. One of the most famous episodes in the history of encryption and cryptanalysis occurred during World War II, in which codebreakers at Bletchley Park, notably Alan Turing, cracked the German Enigma code by developing on the work of Polish mathematician Marian Rejewski.

The ability of the Allied forces to decipher all German communications enabled them to protect shipping lanes, monitor troop movements, and better coordinate attacks, ending the war far sooner than if they had been unable to crack the code. The other famous codebreaking machine to emerge from the work at Bletchley was Colussus, which was used to break the German Lorenz cipher, and later became the forebear of the modern computer.

In recent times, there has been no shortage of government attempts to control the spread of strong encryption, particularly after the invention of Public Key Encryption by Whitfield Diffie. Of particular note is Phil Zimmerman’s public key encryption program PGP (Pretty Good Privacy) which was posted to a Usenet bulletin board as freeware in June 1991 and has since spread across the globe.

Zimmerman wrote and released PGP in 1991 in order to forestall Senate Bill 266, an anticrime bill that would have forced the manufacturers of communications devices using encryption to install back doors through which the government could easily read all correspondence. The distinction of PGP is that it allows individuals with conventional home computers to send RSA-encrypted messages via email that are effectively impossible for intelligence organizations to decode.

By September 1993, Zimmerman was being investigated by the San José Office of U.S. customs for the illegal “export” of his program, a case that was finally dropped. Since the U.S. Department of State classified encryption technologies as “munitions,” to be regulated under the Arms Export Control Tax, Zimmerman was considered an illegal arms exporter.

The eventual furor created by the release of PGP and the investigation of Zimmerman brought the issue into public awareness like never before. On one side, there existed an unlikely union of civil libertarians, privacy advocates, and big business (concerned about corporate security and the protection of Internet transactions).

On the other side, the government and security agencies argued that they would be unable to read the communications of drug cartels and terrorists, thereby hampering their investigation and prosecution of criminals.

Various compromises have been proposed by the U.S. government, such as key escrow, in which all private encryption keys are held by a neutral third party and relinquished to law enforcement bodies in criminal investigations, yet it has not had wide support and the issue of government controls on encryption remains largely undecided.

Although strong encryption has in recent years entered the public domain, the National Security Agency (NSA) is still largely responsible for its development and control. The NSA has stood at the forefront of cryptanalytical science for the last half century and has played a role in almost every encryption-related issue since its inception.

Established in 1952 by the presidential directive of Harry S. Truman, the NSA began its life as the Armed Forces Security Agency (AFSA), eventually expanding to become larger than the CIA. For many years, its name did not appear on any governmental documentation and its budget remains a matter of great secrecy.

Though the NSA is in one sense a modern-day black chamber, it is also the largest information gathering and cryptanalytical body history has ever seen, administering the ECHELON program, employing more mathematicians than any organization in the world, and cryptanalyzing both domestic and international communications for use by U.S. intelligence and law enforcement agencies.

There is also some evidence that it has been involved in industrial espionage by passing on information to U.S. companies in order to win lucrative international contracts. Unsurprisingly, modern conspiracy theories, novels, and films such as Sneakers (1992), Mercury Rising (1998), and Enemy of the State (1998) have cited it, rather than the CIA, as the newly definitive enemy of the people.