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NCSL BULLETIN
Advising users on computer systems technology
July 1990
NCSL Bulletins are published by the National Computer Systems
Laboratory (NCSL) of the National Institute of Standards and
Technology (NIST). Each bulletin presents an in-depth
discussion of a single topic of significant interest to the
information systems community. Bulletins are issued on an
as-needed basis and are available from NCSL Publications,
National Institute of Standards and Technology, B151,
Technology Building, Gaithersburg, MD 20899, telephone (301)
975-2821 or FTS 879-2821.
The following bulletins are available:
Data Encryption Standard, June 1990
GUIDANCE TO FEDERAL AGENCIES
ON THE USE OF
TRUSTED SYSTEMS TECHNOLOGY
INTRODUCTION
Purpose. The purpose of this document is to provide initial
guidance to federal departments and agencies on the use of
trusted systems technology in computer systems which handle
unclassified sensitive information.
Background. The National Institute of Standards and
Technology (NIST) has received many inquiries from federal
agencies regarding the applicability of Department of Defense
(DoD) Standard 5200.28-STD, DoD Trusted Computer Systems
Evaluation Criteria (TCSEC), and National Telecommunications
and Information Systems Security Policy (NTISSP) Number 200,
National Policy on Controlled Access Protection, to computer
systems which are used to process unclassified sensitive
information and which are covered by the Computer Security
Act of 1987 (Public Law 100-235). The TCSEC, often called
the "Orange Book," was developed by the National Computer
Security Center (NCSC) of the National Security Agency (NSA).
NTISSP 200 was published under authority of National Security
Decision Directive (NSDD) 145 prior to the passage of the
Computer Security Act, which established new federal
authorities and policy on protection of unclassified computer
systems.
Authority -- NIST Responsibilities under Computer Security
Act. The Computer Security Act of 1987 assigns NIST the
responsibility for developing security standards and
guidelines for federal computer systems, with the exception
of classified and a specified category of Department of
Defense unclassified systems (referred to as "Warner
Amendment" systems). NIST is therefore responsible for
advising all federal agencies on the use of trusted systems
technology in most unclassified computer systems.
Objectives. Specific objectives of this document are to:
o provide guidance to federal agencies on the use of
trusted systems technology;
o clarify the applicability of the TCSEC and NTISSP
Number 200; and
o describe NIST's long-range plans for the development
of additional policy, guidance, and technical
recommendations on the use of trusted system
technology.
Definition. Trusted Systems Technology - The technical
methods and mechanisms that are used to develop trusted
systems, are used to assure the enforcement of a security
policy in such systems, and are contained within the trusted
systems. Examples of trusted systems are trusted operating
systems, trusted networks, trusted databases, and trusted
applications. Examples of methods are modeling, software
engineering, and automated evaluation. Examples of
mechanisms include identification, authentication, auditing,
and access control.
Applicability. This guidance applies to those federal
computer systems defined in the Computer Security Act of
1987.
POLICY GUIDANCE
Use of Trusted Systems Technology. Each agency should select
computer security controls, including trusted systems
technology, for its systems which are commensurate with the
estimated risk and magnitude of potential loss of
confidentiality, integrity or availability. The selection
should be based upon an analysis of the security risks for
each system within its particular environment. Trusted
systems technology can be particularly useful for agencies
with significant requirements for confidentiality of
computer-based information. It can also provide basic access
control protection to help meet information integrity
requirements.
Applicability of NTISSP Number 200. There is no binding
national policy on the applicability and use of trusted
systems technology in federal computer systems which process
unclassified information. In particular, NTISSP Number 200
does not apply to unclassified systems covered by the
Computer Security Act of 1987.
USE OF TRUSTED SYSTEMS TECHNOLOGY
Value of Trusted Systems. NIST recommends the use of trusted
systems technology when such technology satisfies
requirements for adequate and cost-effective access control
protection. Such requirements exist when there is a need for
safeguarding the confidentiality and integrity of
information. In addition, the assurance process which is a
part of trusted systems technology can help support system
availability requirements. All these requirements should be
planned for and validated by a formal risk management
procedure. As an integral part of the planning process
required by the Computer Security Act, the first step in risk
management is the conduct of a thorough risk analysis. The
second step in risk management is selection of appropriate
security controls based on the analysis of the security risks
for the environment involved. This risk management process
should balance security and performance requirements and
provide for cost-effective security and privacy of sensitive
information in the system. Effective use of trusted systems
technology, like any other security control, should
substantially increase the protection relative to the
additional acquisition, operating and maintenance costs of
the security mechanisms obtained.
Computer Security Planning and Protection Strategy. A
security protection strategy consists of a mix of physical,
administrative, and technical safeguards, including trusted
systems technology. The use of trusted system technology can
be an effective part of a larger computer security protection
strategy for satisfying confidentiality, integrity, and
availability requirements. As with other types of protection
mechanisms, the benefits attainable from trusted systems
technology can only be realized if these mechanisms are used
properly in a complementary fashion.
Use of Evaluated Products. Agencies with a need for systems
with trusted technology features should select those systems
from NSA's Evaluated Products List (EPL). If EPL products
are not available, then agencies may select or design systems
that best meet their security requirements using the TCSEC as
a guide. NSA's Information Systems Security Products and
Services Catalog contains the EPL, which lists evaluated
products, those systems that are currently undergoing
evaluation, and the current status of such evaluations.
Use of Class "C2" Systems. Systems designed to meet "C2" or
higher classes of the TCSEC should first be considered when
acquiring multi-user computer systems with a requirement to
control user access to information according to "need to
know" and authorization. The "C2" and other TCSEC criteria
were designed to achieve confidentiality through improved
access control. The same access control mechanisms can also
be beneficial for helping to maintain information integrity.
While it should be recognized that access controls are a
necessary part of achieving integrity and availability, there
are other requirements for integrity and availability not
covered by the TCSEC. NIST recommends that federal
departments and agencies consider using "C2" functionality as
a minimum to help protect their multi-user systems having
confidentiality or integrity control requirements.
Use of Division "B" Systems. When acquiring multi-user
computer systems with a requirement for mandatory separation
of sensitive information and for which security labels can be
established, systems designed to meet the criteria of the "B"
division of the TCSEC can be useful. Systems in that
division are designed to enforce a mandatory access control
or multi-level security policy. However, the cost benefit
considerations discussed earlier are of particular importance
when considering the use of "B" division level systems. In
the context of this guidance document, the term "security
label" is used to denote confidentiality, integrity, or
availability categories established pursuant to a larger
organizational information security policy. Security labels
are a generalization of the "sensitivity labels" used in the
TCSEC.
NIST PLANS FOR DEVELOPMENT OF TRUSTED SYSTEMS GUIDANCE
NIST recognizes that federal agencies in their unclassified
computer security programs will require additional guidance
on the use of trusted systems technology as it evolves. NIST
has an active program to develop such guidance. This section
describes some of the current activities designed to provide
this guidance over the next few years.
National Evaluation Criteria. NIST plans to publish guidance
on information and system integrity, focusing first on
technical methods of achieving effective integrity controls
in computer and telecommunications systems. NIST recognizes
the benefits of TCSEC evaluated products and will work
closely with NSA and other private and public sector
organizations to create a set of national evaluation criteria
that will emphasize integrity and availability to complement
the TCSEC. NIST will work with NSA to extend NSA's
evaluation program to incorporate these methods into trusted
systems.
Security Criteria for Distributed Systems. NIST and NSA are
studying the need for security criteria in distributed
computer systems to address integrity, availability and
confidentiality of unclassified information.
Security Labels. NIST also plans to work with government
organizations and industry in developing suggested standard
categories of data to which security labels, which would
control the handling of that data, can be applied. The
labels can be applied to categories of unclassified
government and commercial information that require protection
for confidentiality, integrity and availability purposes.
These labels can then be used with "B" division trusted
systems. Note that any security labeling scheme should
complement an organization's information protection policy.
Guide to Use of Trusted Systems Technology. NIST is
preparing additional guidance to assist federal agencies in
deciding how to use trusted systems technology to protect
computer systems containing unclassified sensitive
information. This guide will include more detailed
information on the extent to which that technology provides
system-level confidentiality, integrity and availability
protection for unclassified systems. The guide will stress
the key point that the risk analysis-based process of
identifying valid information protection requirements is an
essential prerequisite for determining the full set of
protection mechanisms (trusted systems included) to be
effectively applied to computer systems. This guide can be
viewed as complementing the NSA's "Yellow Book" (CSC-STD-004-
85, Guidance for Applying the DoD Trusted Computer System
Evaluation Criteria in Specific Environments, June 25, 1985),
which addresses the use of trusted technology in systems
processing classified information.
International Evaluation Criteria. NIST is participating in
international computer security standards activities that are
specifying a wide range of security services and mechanisms
in information technology. NIST recognizes the efforts and
contributions of numerous international organizations
presently developing security architectures, profiles, and
criteria. Specifically, NIST is reviewing the Information
Technology Security Evaluation Criteria (ITSEC) that have
been proposed for European Community use and is preparing
comments on their utility for U.S. Government unclassified
applications.
REFERENCE DOCUMENTS
Computer Security Act. The Computer Security Act of 1987 was
signed into law on January 8, 1988, therefore superseding
NTISSP Number 200 for systems processing sensitive
unclassified information. It established NIST's authority to
develop uniform technical, management, physical, and
administrative standards and guidelines for the cost-
effective security and privacy of sensitive information in
federal computer systems, except those systems processing
classified or Warner Amendment information. The Act also
prescribed a process whereby agencies are required to prepare
plans for the security and privacy of federal computer
systems containing sensitive information.
NSDD-145. National Security Decision Directive (NSDD) 145,
National Policy on Telecommunications and Automated
Information Systems Security, was issued on September 17,
1984. NSDD-145 required federal agencies to establish
policies, procedures, and practices to protect national
security related information in computer systems. NSDD-145
established the National Telecommunications and Information
Systems Security Committee (NTISSC) to develop and issue
national system security operating policies.
NTISSP Number 200. The NTISSC issued NTISSP Number 200 on
July 15, 1987. NTISSP 200 required multi-user computer
systems containing classified or unclassified sensitive
information operated by federal agencies and their
contractors to have "controlled access protection" as a
minimum level of security protection. Controlled access
protection is technically defined in the TCSEC as the "C2"
class of trust. Further, NTISSP 200 required federal
agencies and contractors to provide this controlled access
protection in automated information systems containing
sensitive information within five years (hence the well-known
phrase "C2 by '92").
NIST'S COMPUTER SECURITY PROGRAM
For further information regarding other aspects of NIST's
computer security program, including NIST's federal agency
assistance program, please contact:
Computer Security Division
National Computer Systems Laboratory
Building 225, Room A216
National Institute of Standards and Technology
Gaithersburg, MD 20899
Telephone (301) 975-2934
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