Choosing the correct data to encrypt is specific to your database and application requirements, but consider the following when selecting objects to encrypt:
For data in a Type I area, you must encrypt the entire area, even if only one field in one table must be encrypted. Consider moving the table with the critical field, and its indexes to a Type II area, so that you can encrypt only the critical table and indexes.
For tables in a Type II area, understand the contents of the table's indexes to determine if the index needs to be encrypted. For example, if you have an employee table with a social security number field and a separate employee number field, if the social security number field is used in an index, the index should be encrypted. However, if you have an index on the employee number field, you may determine that it is not necessary to encrypt that index.
