It is best to choose an encryption key value that cannot be easily guessed. The key can be of arbitrary length, but generally the longer the key, the better because a shorter key is easier to guess than a longer one. As well, including a combination of numbers, letters, and special characters decreases the chances of someone guessing the key.

Encryption keys are always case sensitive, and they cannot contain leading or trailing spaces or semicolons.

You must supply this key each time you want to start the database. Lost or forgotten keys result in completely inaccessible databases.

You can choose whether the encryption key is entered at the command prompt (the default) or into a prompt box. Choosing to enter the key in a prompt box provides an extra measure of security because the key is never visible in plain sight. Clients are required to specify the key each time they start the database. In cases where the database administrator starts the database, clients never need to have access to the key. See -ep server option.

You can change the encryption key for an encrypted database, or for a database for which table encryption has been enabled, using the CREATE ENCRYPTED DATABASE statement. As with encrypting the database, you are not overwriting the existing file, you are creating a copy of the file, encrypted with the new key.

To change the encryption key for a database

• Change the encryption key for an encrypted database using the CREATE ENCRYPTED DATABASE statement.

  The following example takes the database file myOldDatabase.db, encrypted with key abc, and creates a copy of it called myNewDatabase.db, encrypting it with the key abc123. Any other database-related files (transaction log, transaction log mirrors, dbspace files) are also created using the new encryption key. See CREATE ENCRYPTED DATABASE statement.

  CREATE ENCRYPTED DATABASE myNewDatabase.db FROM myOldDatabase.db KEY 'abc123' OLD KEY 'abc' ALGORITHM 'AES';