How is polyinstantiation used to secure a multilevel database?

A.
It prevents low-level database users from inferring the existence of higher level data.

B.
It confirms that all constrained data items within the system conform to integrity specifications.

C.
It ensures that all mechanism in a system are responsible for enforcing the database security
policy.

D.
Two operations at the same layer will conflict if they operate on the same data item and at least
one of them is an update.

Explanation:
“Polyinstantiation is the development of a detailed version of an object from another
object using different values in the new object. In the database information security, this term is
concerned with the same primary key for different relations at different classification levels being
stored in the same database. For example, in a relational database, the same of a military unit
may be classified Secret in the database and may have an identification number as the primary
key. If another user at a lower classification level attempts to create a confidential entry for another
military unit using the same identification number as a primary key, a rejection of this attempt
would imply to the lower level user that the same identification number existed at a higher level of
classification. To avoid this inference channel of information, the lower level user would be issued
the same identification number for their unit and the database management system would manage
this situation where the same primary key was used for different units.” Pg 352-353 Krutz: The
CISSP Prep Guide: Gold Edition.
“Polyinstantiation occurs when to or more rows in the same table appear to have identical primary
key elements but contain different data for use at differing classification levels. Polyinstantiation is
often used as a defense against some types of inference attacks.
For example, consider a database table containing the location of various naval ships on patrol.

Normally, this database contains the exact position of each ship stored at the level with secret
classification. However, on particular ship, the USS UpToNoGood, is on an undercover mission to
a top-secret location. Military commanders do not want anyone to know that the ship deviated from
its normal patrol. If the database administrators simply change the classification of the
UpToNoGood’s location to top secret, a user with secret clearance would know that something
unusual was going on when they couldn’t query the location of the ship. However, if
polyinstantiation is used, two records could be inserted into the table. The first one, classified at
the top secret level, would reflect the true location of the ship and be available only to users with
the appropriate top secret security clearance. The second record, classified at the secret level,
would indicate that the ship was on routine patrol and would be returned to users with a secret
clearance.”
Pg. 191 Tittel: CISSP Study Guide Second Edition