Oracle PL/SQL for DBAs

Using a Single Key

With this approach, a single key is used to access any data in the database. As shown in Figure 4-3, the encryption routine reads only one key from the key location and encrypts all the data that needs to be protected. This key could be stored in a variety of locations:

In the database

This is the simplest strategy of all. The key is stored in a relational table, perhaps in a schema used specifically for this purpose. Because the key is inside the database, it is automatically backed up as a part of the database; older values can be obtained by flashback queries or the database, and the key is not vulnerable to theft from the operating system. The simplicity of this approach is also its weakness: because the key is just data in a table, anyone with the authority to modify that table (such as any DBA) could alter the key and disrupt the encryption infrastructure.

In the filesystem

The key is stored in a file, which may then be read by the encryption procedure, using the UTL_FILE built-in package. By setting the appropriate privileges on that file, you can ensure that it cannot be changed from within the database.

On some removable media controlled by the end user

This approach is the safest one; no one except the end user can decrypt the values or alter the key, not even the DBA or system administrator. Examples of removable media include a USB stick, a DVD, and a removable hard drive. A major disadvantage of removable media is the possibility of key loss or key ...