Which document is key for outlining the requirements for marking classified information?

The correct choice is significant because Executive Order 13526 specifically outlines the framework for classifying national security information and includes detailed requirements for the marking of classified information. It establishes the rules and procedures necessary for the classification system, ensuring that individuals handling classified information understand how to appropriately mark documents based on their sensitivity and classification level. These marking requirements include the appropriate classification level (Top Secret, Secret, or Confidential), as well as any additional handling and dissemination instructions that pertain to the classified content.

In contrast, the other documents mentioned provide valuable context or guidelines for various aspects of national security and intelligence operations but do not serve as the primary source for the specific requirements on marking classified information. The National Security Strategy is more focused on overarching security objectives rather than marking protocols; the Department of Defense Directive 5200.1 addresses broader security and information management policies; and the Intelligence Authorization Act primarily pertains to funding and oversight of intelligence activities, not classification marking specifics. Thus, Executive Order 13526 is the essential document for understanding how classified information should be marked.