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TCSEC: The Orange Book
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
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