To determine a correct way to protect classified data, the most reliable approach is to follow established, government-aligned practices that emphasize need-to-know access, proper labeling, secure storage, and strong technical controls. Direct answer:

• Store classified data only in approved, secure environments (for example, in a container or vault that meets applicable government standards) and ensure access is restricted to individuals with appropriate clearance and need-to-know.

• Enforce strict access controls and verification before granting access, applying the principle of least privilege and using multi-factor or other strong authentication as part of identity verification.

• Protect data at rest and in transit with appropriate encryption, and apply usage controls to prevent unauthorized copying, sharing, printing, or modification.

• Ensure data handling is documented with proper classification markings, and that personnel are trained on handling, sharing, and declassification procedures.

If you’d like, I can tailor the guidance to a specific agency, country, or scenario (e.g., physical vault storage vs. digital encryption, or a particular data classification level).