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6 – Transparent Data EncryptionTDE and DecryptionTDE is designed to protect data at rest by encrypting the physical data filesrather than the data itself. This level of protection prevents the data and backupfiles from being opened in a text editor to expose the file's contents.TDE encryption occurs prior to writing data to disk, and the data is decryptedwhen it is queried and recalled into memory. This encryption and decryptionoccurs without any additional coding or data type modifications; thus it’stransparency. Once the data is recalled from disk, into memory, it is no longerconsidered to be at rest. It has become data in transit, which is beyond thescope of this feature. As such, alongside TDE, you should consider applyingadditional supporting layers of protection to your sensitive data, to ensurecomplete protection from unauthorized disclosure. For example, you may wishto implement, in addition to TDE, encrypted database connections, cell-levelencryption, or one-way encryption. For additional data in transit protection thatis required, externally from the database, you may need to consult with, ordefer to, your Network Administration team.Backup and RecoveryAs noted previously, TDE prevents the backup files from being opened by aplain text editor. It also limits the recovery of the database backup file to theinstance that holds the encryption key hierarchy that was in existence at thetime the backup was created.As illustrated in Figure 6-1, backup files of databases with TDE enabled areencrypted using a key hierarchy that includes the service master key of theSQL Server instance, the database master key and certificate for the Masterdatabase.Despite this dependency, none of these keys are included with the standarddatabase backup, and must be backed up separately via the followingcommands (see Listing 4-8, in Chapter 4, for example usage):• BACKUP SERVICE MASTER KEY to backup of the service masterkey.• BACKUP MASTER KEY to backup of a database master key.• BACKUP CERTIFICATE to backup the certificate.This behavior is one of the security benefits of TDE. In order to restore theencrypted data to another instance of SQL Server, a user needs to recover theservice master key backup file, the Master database master key backup file132