Understanding Relational Databases and Assessing Their Security - High-Performance Web Databases: Design, Development, and Deployment - page 765

system mechanisms for user identification and authentication so that
users need only identify themselves once to the operating system, rather
than to both operating system and the database system. Users must
remember only one password; passwords are sorted only once, and audit
trail records reflect a one-to-one mapping between operating system users
and database users.
Vendors are also beginning to provide database audit capabilities that
meet TCSEC class C2 criteria. Several products now offer auditing of state-
ment executions or failures, auditing of objects, auditing of individual users
or groups of users, and auditing of audit trail management. This ability to
specify areas to be audited should result in more concise audit reporting
and reduce the need for additional tools for audit trail analysis. However,
extensive use of these more comprehensive audit capabilities may degrade
system performance and increase the time required for audit trail review;
consequently, audit options should be carefully selected and used. Audit
features should permit the auditor to examine only those actions neces-
sary to ensure system security.
The ability to enforce limits on the use of database system resources can
also enhance security. For example, the database administrator can set lim-
its on the number of concurrent sessions allowed per use of the database,
idle time per session, Central Processing Unit use, and logical block reads.
In some systems, this can be done by specifying a resource limit profile for
either individual users or roles. The use of such profiles can help protect
against denial of service and ensure the availability of system resources.
For example, limits can be imposed to control the use of long-running,
resource-intensive queries during peak hours.
Database Integrity Controls
Four principal types of data integrity controls-referential integrity, trans-
action integrity, entity integrity, and value constraints-are supported in
varying degrees by relational database products. It should be noted that
database integrity is of particular importance in multilevel secure environ-
ments, as is discussed later in this chapter.
Referential integrity controls involve the comparison of a foreign key
value to a primary key value. In the case of relational databases, for exam-
ple, a rule may be defined for a column of a table to permit modification of
a row only if the foreign key value associated with the column matches the
primary key value associated with a column of a related table. In Exhibit 2,
for example, to ensure that all department numbers assigned to employ-
ees are valid, the foreign key value DEPTNO from the column in the
EMPLOYEE table containing the department identification number of each
employee is compared with the primary key value DEPTNO in the column
of the DEPARTMENT table containing all valid department numbers. Some