The National Security Agency/Central Security Service (NSA/CSS) is the United States government's cryptologic organization that was officially established on November 4, 1952. Responsible for the collection and analysis of foreign communications, it coordinates, directs, and performs highly specialized activities to produce foreign signals intelligence information, which involves a significant amount of cryptanalysis. It is also responsible for protecting U.S. government communications and information systems from similar agencies elsewhere, which involves a significant amount of cryptography.
A component of the Department of Defense, the NSA has always been directed by a three-star flag officer. The NSA is a key component of the U.S. Intelligence Community, which is headed by the Director of National Intelligence.
Contrary to popular perception, the NSA does not engage in “wiretapping”; it collects signals intelligence, or “sigint.” In contrast to the image we have from movies and television of an FBI agent placing a listening device on a target’s phone line, the NSA intercepts entire streams of electronic communications containing millions of telephone calls and e-mails. It runs the intercepts through very powerful computers that screen them for particular names, telephone numbers, Internet addresses, and trigger words or phrases. Any communications containing flagged information are forwarded by the computer for further analysis.
The NSA's eavesdropping mission includes radio broadcasting, both from various organizations and individuals, the Internet, telephone calls, and other intercepted forms of communication. Its secure communications mission includes military, diplomatic, and all other sensitive, confidential or secret government communications. Despite having been described as the world's largest single employer of mathematicians, and the owner of the single largest group of supercomputers, it has tried to keep a low profile. For many years its existence was not even acknowledged by the U.S. government. It was often said, half-jokingly, that "NSA" stood for "No Such Agency", and also, as "Never Say Anything", primarily for its employees.
Because of its listening task, the NSA/CSS has been heavily involved in cryptanalytic research, continuing the work of its predecessor agencies which had been responsible for breaking many World War II codes and ciphers (see, for instance, Purple code, Venona, and JN-25).