RESTORE MASTER KEY (Transact-SQL)
Imports a database master key from a backup file.
When the master key is restored, SQL Server decrypts all the keys that are encrypted with the currently active master key, and then encrypts these keys with the restored master key. This resource-intensive operation should be scheduled during a period of low demand. If the current database master key is not open or cannot be opened, or if any of the keys that are encrypted by it cannot be decrypted, the restore operation fails.
Use the FORCE option only if the master key is irretrievable or if decryption fails. Information that is encrypted only by an irretrievable key will be lost.
If the master key was encrypted by the service master key, the restored master key will also be encrypted by the service master key.
If there is no master key in the current database, RESTORE MASTER KEY creates a master key. The new master key will not be automatically encrypted with the service master key.

