Encryption-Based Multilevel Model for DBMS - Multilevel Security for Relational Databases - page 90

5.2 The Encryption-Based Multilevel Database Model

In the encryption-based multilevel database model, a symmetric
key is created for each unique security level and used to encrypt or
decrypt the data in the multilevel relational database. This key is
defined automatically by the model during the creation of the security
level. The user can use the keys that are defined to the security levels
lower than or equal to his security level. A multilevel relation scheme
is denoted by

, where each A i is a
data attribute over domain D i , each C i is a classification attribute for
A i , and E Ci (A i ) is the encryption function for A i by the key accord-
ing to the classification security level C i.
In this model, the classification attributes for the multilevel rela-
tional database are removed and each attribute is encrypted by using
the encryption key that corresponds to the tuple security classification
level (tuple level encryption).
This removing of the classification attributes from the multilevel
database results in reducing the multilevel relational database size.
Tables 5.1 and 5.2 illustrate an example showing how the data are
stored in the MLR model and in the proposed encryption-based mul-
tilevel model. In the proposed model, adding the encryption system
to the MLR model led to solving the problems in the MLR model
by removing the classification attributes from the multilevel database
and then reducing the multilevel database size and making the data-
base administration easier.
The encryption algorithm is supported in several commercial
database management systems like DB2 (IBM) and ORACLE.
In DB2 (IBM) [61], encryption has been performed by implement-
ing SQL functions and stored procedures that help to encrypt and
decrypt the data. The user will supply the encryption key to be used
in encrypting the data during the insertion into the relational data-
base. When the data are retrieved, the same password should be
supplied to decrypt the data. In ORACLE [62], transparent data
encryption helps to encrypt the sensitive data stored in relations in
the database. Only the user who has access to the encrypted data
can decrypt it.
Table 5.3 shows a comparison between the encryption-based
multilevel database model and the commercial database systems like

R(E(A),E (A ), ,E (A ),TC) … C1 C2 Cn 1 2 n