The usefulness of the Internet for commercial and industrial purposes depends on the ability of individuals and companies to communicate privately, using an intrinsically public medium. People have to be able to count on the fact that credit card information, bank and brokerage transactions, medical records, and other sensitive data can be safely hidden from the outside world, yet be readable by the intended recipient. "Crypto" is a history of how the "public key" system that makes this possible was invented by a group of computer programmers working outside of and in competition with the US National Security Agency (NSA). Government agencies, and especially NSA, tried to keep the technology secret, and to limit the degree of security available to a level that would be "crackable" by them, because truly secret codes also allow criminals and terrorists to communicate secretly. One can only wonder what the consequences for individual freedom would have been, had the technology had not been largely settled before September 11, 2001. (The cloth version of the book was published in 2000.) For more on those important issues, see the Web pages of theElectronic Frontier Foundation.