Cryptography—the art and science of secret writing, has belonged to governments concerned about protecting their own secrets and asserting their prerogatives for access to information relevant to national security and public safety. Countries needs for effective cryptographic protection of classified and other sensitive communications, as well as their needs to gather intelligence for national security purposes, would be damaged by the widespread use of cryptography. National security concerns have motivated such actions as the development of cryptographic technologies, the development of countermeasures to reverse the effects of encryption, and the control of cryptographic technologies for export. In the last three decades, a number of developments have brought about what could be called the popularization of cryptography.
