TCSEC Trusted Computer System Evaluation Criteria
TCSEC Purpose -Establish best practices -Requirements for assessing the effectiveness of security controls -Measure computing resource security -Evaluate, classify, and select systems considered for computing resources
TCSEC: Purpose Guidance – provides guidance on how to design a trusted computing system along with their associated data and services Metrics – provides a metric (classification) for determining the level of trust assigned to a computing system.
Orange Book: Metrics Measurement of a system's security is quantified using a classification system. The Classes are: D C1 & C2 B1, B2, B3 A1 A is more secure than D 2 is more secure than 1.
Orange Book: Metrics The rating system is hierarchical D applies to any system that fails to meet any of the higher level security classes. The other levels have increasing security requirements. A1 systems would be rare.
Disclaimer An A1 system is not 100% secure. The risk level is expected to be lower compared to the other levels
Metrics: C1 Identification and authentication (user id & password) DAC – (Discretionary Access Controls) – capable of enforcing access controls – Example: Basic Unix/Linux OS, user, group, other.
Metrics: C2 C1 plus Audit trails System documentation and user manuals.
Metrics B1 C2 plus Discovered weaknesses must be mitigated
Metrics B2 B1 plus Security policy must be defined and documented Access controls for all subjects and objects
Metrics: B3 B2 plus Automated imminent intrusion detection, notification and response.
Metrics: A1 B3 + System is capable of secure distribution (can be transported and delivered to a client with the assurance of being secure)
Orange Book Security Criteria Security Policy Accountability Assurance Documentation
1. Security Policy The set of rules and practices that regulate how an organization manages, protects, and distributes information.
1. Security Policy The policy is organized into subjects and objects. Subjects act upon objects Subjects – processes and users. Objects – data, directories, hardware, applications A well defined access control model determines if a subject can be permitted access to an object.
Security Policy Top secret, secret, classified, non-classified Need-to-know, job division, job rotation, NDA, etc.
2. Accountability The responsibilities of all who come in contact with the system must be well defined. Identification (… the process to identify a user) Auditing (...accumulating and reviewing log information and all actions can be traced to a subject) Organizational chart Job description contract, AUP, NDA, SLA
3. Assurance The reasonable expectation that the security policy of a trusted system has been implemented correctly and works as intended. Assurance is organized into Operational assurance Life-cycle assurance
3a. Organizational Assurance Security policy is maintained in the overall design and operation of the system. Example: Users of the system have an assurance that access controls are enforced
3b. Life-cycle Assurance Insuring the system continues to meet the security requirements over the lifetime of the system. Updates to the software and hardware must be considered The expectation that the system remains operational (is available) over its lifetime Sustainability-cycle
4. Documentation Requirements Security Features User's Guide Trusted Facility Manual Test Documentation Design Documentation
Documentation: Security Features User's Guide Aimed at the ordinary (non-privileged) users. General usage policy *Instructions on how to effectively use the system Description of relevant security features
Documentation: Trusted Facility Manual Aimed at the S.A. Staff How the system is configured and maintained Includes the day-to-day required activities Backups Reviewing security logs
Documentation: Test Documentation Instructions on how to test the required security mechanisms
Documentation: Design Documentation Define the boundaries of the system A complete description of the hardware and software. Complete system design specifications Description of access controls
The Orange Book The Orange book has been superseded by the Common Criteria