Ancient Assyria also used cryptography, including the unique and curious custom of "funerary cryptography." Assyrian tombs sometimes featured odd sets of cryptographic cuneiform symbols. The Assyrian passerby, puzzling out the import of the text, would mutter the syllables aloud, and find himself accidentally uttering a blessing for the dead. Funerary cryptography was a way to steal a prayer from passing strangers.
Julius Caesar lent his name to the famous "Caesar cypher," which he used to secure Roman military and political communications.
Modern cryptographic science is deeply entangled with the science of computing. In 1949, Claude Shannon, the pioneer of information theory, gave cryptography its theoretical foundation by establishing the "entropy" of a message and a formal measurement for the "amount of information" encoded in any stream of digital bits. Shannon's theories brought new power and sophistication to the codebreaker's historic efforts. After Shannon, digital machinery could pore tirelessly and repeatedly over the stream of encrypted gibberish, looking for repetitions, structures, coincidences, any slight variation from the random that could serve as a weak point for attack.
Computer pioneer Alan Turing, mathematician and proponent of the famous "Turing Test" for artificial intelligence, was a British cryptographer in the 1940s. In World War II, Turing and his colleagues in espionage used electronic machinery to defeat the elaborate mechanical wheels and gearing of the German Enigma code- machine. Britain's secret triumph over Nazi communication security had a very great deal to do with the eventual military triumph of the Allies. Britain's code-breaking triumph further assured that cryptography would remain a state secret and one of the most jealously guarded of all sciences.
After World War II, cryptography became, and has remained, one of the crown jewels of the American national security establishment. In the United States, the science of cryptography became the high-tech demesne of the National Security Agency (NSA), an extremely secretive bureaucracy that President Truman founded by executive order in 1952, one of the chilliest years of the Cold War.
Very little can be said with surety about the NSA. The very existence of the organization was not publicly confirmed until 1962. The first appearance of an NSA director before Congress was in 1975. The NSA is said to be based in Fort Meade, Maryland. It is said to have a budget much larger than that of the CIA, but this is impossible to determine since the budget of the NSA has never been a matter of public record. The NSA is said to the the largest single employer of mathematicians in the world. The NSA is estimated to have about 40,000 employees. The acronym NSA is aptly said to stand for "Never Say Anything."
The NSA almost never says anything publicly. However, the NSA's primary role in the shadow-world of electronic espionage is to protect the communications of the US government, and crack those of the US government's real, imagined, or potential adversaries. Since this list of possible adversaries includes practically everyone, the NSA is determined to defeat every conceivable cryptographic technique. In pursuit of their institutional goal, the NSA labors (in utter secrecy) to crack codes and cyphers and invent its own less breakable ones.
The NSA also tries hard to retard civilian progress in the science of cryptography outside its own walls. The NSA can suppress cryptographic inventions through the little-known but often-used Invention Secrecy Act of 1952, which allows the Commissioner of Patents and Trademarks to withhold patents on certain new inventions and to order that those inventions be kept secret indefinitely, "as the national interest requires." The NSA also seeks to control dissemination of information about cryptography, and to control and shape the flow and direction of civilian scientific research in the field.
Cryptographic devices are formally defined as "munitions" by Title 22 of the United States Code, and are subject to the same import and export restrictions as arms, ammunition and other instruments of warfare. Violation of the International Traffic in Arms Regulations (ITAR) is a criminal affair investigated and administered by the Department of State. It is said that the Department of State relies heavily on NSA expert advice in determining when to investigate and/or criminally prosecute illicit cryptography cases (though this too is impossible to prove).
The "munitions" classification for cryptographic devices applies not only to physical devices such as telephone scramblers, but also to "related technical data" such as software and mathematical encryption algorithms. This specifically includes scientific "information" that can be "exported" in all manner of ways, including simply verbally discussing cryptography techniques out loud. One does not have to go overseas and set up shop to be regarded by the Department of State as a criminal international arms trafficker. The security ban specifically covers disclosing such information to any foreign national anywhere, including within the borders of the United States.
These ITAR restrictions have come into increasingly harsh conflict with the modern realities of global economics and everyday real life in the sciences and academia. Over a third of the grad students in computer science on American campuses are foreign nationals. Strictly appled ITAR regulations would prevent communication on cryptography, inside an American campus, between faculty and students. Most scientific journals have at least a few foreign subscribers, so an exclusively "domestic" publication about cryptography is also practically impossible. Even writing the data down on a cocktail napkin could be hazardous: the world is full of photocopiers, modems and fax machines, all of them potentially linked to satellites and undersea fiber-optic cables.
In the 1970s and 1980s, the NSA used its surreptitious influence at the National Science Foundation to shape scientific research on cryptography through restricting grants to mathematicians. Scientists reacted mulishly, so in 1978 the Public Cryptography Study Group was founded as an interface between mathematical scientists in civilian life and the cryptographic security establishment. This Group established a series of "voluntary control" measures, the upshot being that papers by civilian researchers would be vetted by the NSA well before any publication.
This was one of the oddest situations in the entire scientific enterprise, but the situation was tolerated for years. Most US civilian cryptographers felt, through patriotic conviction, that it was in the best interests of the United States if the NSA remained far ahead of the curve in cryptographic science. After all, were some other national government's electronic spies to become more advanced than those of the NSA, then American government and military transmissions would be cracked and penetrated. World War II had proven that the consequences of a defeat in the cryptographic arms race could be very dire indeed for the loser.
So the "voluntary restraint" measures worked well for over a decade. Few mathematicians were so enamored of the doctrine of academic freedom that they were prepared to fight the National Security Agency over their supposed right to invent codes that could baffle the US government. In any case, the mathematical cryptography community was a small group without much real political clout, while the NSA was a vast, powerful, well-financed agency unaccountable to the American public, and reputed to possess many deeply shadowed avenues of influence in the corridors of power.
However, as the years rolled on, the electronic exchange of information became a commonplace, and users of computer data became intensely aware of their necessity for electronic security over transmissions and data. One answer was physical security -- protect the wiring, keep the physical computers behind a physical lock and key. But as personal computers spread and computer networking grew ever more sophisticated, widespread and complex, this bar-the-door technique became unworkable.