This lecture covers the Bell La Padula model for confidentiality, covert channels, and the challenges of declassification. It explains security models as design patterns for specific security properties, focusing on the Bell-La Padula model's protection of confidentiality. The classification of objects and subjects, dominance relationships, and the importance of clearance levels are discussed. The lecture also delves into the properties of the BLP system, including the ss-property, *-property, and ds-property. It concludes with the Basic Security Theorem and the limitations of the Bell La Padula model, emphasizing the need for dynamic systems to address changing security needs.