The NSA leads the U.S. government in cryptology that encompasses both signals intelligence (SIGINT) and information assurance (IA). The SIGINT mission collects, processes and disseminates intelligence information from foreign signals for intelligence and counterintelligence purposes, and to support military operations. The IA mission is to prevent foreign adversaries from gaining access to sensitive or classified national security information.
Back in 2009, I went after a copy oft the official employee manual. It was released to me in 2011.
National Security Agency (NSA) Employee Manual (2011 Release) [130 Pages, 19.2MB]