The White House, National Security Directive 42 (NSD 42): National Policy for the Security of National Security Telecommunications and Information Systems (July 5, 1990) (full-text).
The NSD 42 established the National Security Telecommunications and Information Systems Security Committee, now called the Committee on National Security Systems (CNSS), which provides a forum for the discussion of policy issues, sets national policy, and provides direction, operational procedures, and guidance for the security of national security systems.
The Department of Defense chairs the committee. The Secretary of Defense and the Director of the National Security Agency act as the Executive Agent and National Manager for national security systems, respectively.
Among other assignments, NSD 42 directs the CNSS to provide system security guidance for national security systems to executive departments and agencies; and submit annually to the Executive Agent an evaluation of the security status of national security systems. NSD 42 also directs the Committee to interact, as necessary, with the National Communications System Committee of Principals.