The NSA is the National Security Agency (once called “No Such Agency” or “Never Say Anything,” but they've been more open recently), the official security body of the U.S. government. President Harry Truman created the agency in 1952 under the Department of Defense, and for many years its very existence was kept secret. The NSA is concerned with signals intelligence; its mandate is to listen in on and decode all foreign communications of interest to the security of the United States.
The following paragraphs are excerpted from NSA's original charter, signed by President Truman in 1952, and classified for many years thereafter :
The COMINT mission of the National Security Agency (NSA) shall be to provide an effective, unified organization and control of the communications intelligence activities of the United States conducted against foreign governments, to provide for integrated operational policies and procedures pertaining thereto. As used in this directive, the terms “communications intelligence” or “COMINT” shall be construed to mean all procedures and methods used in the interception of communications other than foreign press and propaganda broadcasts and the obtaining of information from such communications by other than intended recipients, but shall exclude censorship and the production and dissemination of finished intelligence.
The special nature of COMINT actives requires that they be treated in all respects ...