(National Computer Security Center) The arm of the U.S. National Security Agency that defines criteria for trusted computer products, which are embodied in the Orange Book and Red Book. Published in the 1980s and 1990s and known as the Rainbow Series because of their colored covers for each topic, they have been largely superseded by the Common Criteria. See also NCSA. Orange Book The Orange Book contains the "Trusted Computer Systems Evaluation Criteria" (TCSEC), DOD Standard 5200.28. Red Book (for networks) The Red Book contains the "Trusted Network Interpretation of the Trusted Computer System Evaluation Criteria" (NCSC-TG-005) and "Trusted Network Interpretation Environments Guideline: Guidance for Applying the Trusted Network Interpretation" (NCSC-TG-011). Level D Systems are rated on a scale starting from D, which is not secure, to A, which is the most secure. Level D is a non-secure system. Level C Level C provides discretionary access control (DAC). The owner of the data can determine who has access to it. C1: Requires user login, but allows group ID. C2: Requires individual user login with password and an audit mechanism. Levels B and A Levels B and A provide mandatory access control (MAC). Access is based on standard DOD clearances. Each data structure contains a sensitivity level, such as top secret, secret and unclassified, and is available only to users with that level of clearance. B1: DOD clearance levels. B2: Guarantees path between user and the security system. Provides assurances that system can be tested and clearances cannot be downgraded. B3: System is characterized by a mathematical model that must be viable. A1: System is characterized by a mathematical model that can be proven. Highest security. Used in military computers.