Server Master Key
It is used to encrypt DMK.
It is created when we install MS SQL.
It is protected by AES algorithm with 256 length.
Single SMK defined for each instance of SQL Server.

Show current SMK

USE master
select * from sys.symmetric_keys

Backup SMK
Backup SMK named as SMK.dat at SQL Server’s C:\SMK\ with password ‘P@ssw0rd’

BACKUP SERVICE MASTER KEY TO FILE = 'C:\SMK\SMK.dat' ENCRYPTION BY PASSWORD = 'P@ssword'

Restore SMK
When we restore SMK, SQL Server will decrypt all key and then use the restored SMK to encrypt all key again.
If the decryption fail, the restored will fail.
We use force restore but it will cause loss of data.

-- Normal Restore
RESTORE SERVICE MASTER KEY FROM FILE = 'C:\SMK\SMK.dat' DECRYPTION BY PASSWORD = 'P@ssword'
-- Force Restore (will cause loss of data)
RESTORE SERVICE MASTER KEY FROM FILE = 'C:\SMK\SMK.dat' DECRYPTION BY PASSWORD = 'P@ssword' FORCE

Regenerate of SMK.
When we regenerate SMK, SQL Server will decrypt all key and then use the restored SMK to encrypt all key again.
If the decryption fail, the regenerate will fail.
We use force regenerate but it will cause loss of data.

-- Normal Regenerate
ALTER SERVICE MASTER KEY REGENERATE
-- Force Regenerate (will cause loss of data)
ALTER SERVICE MASTER KEY FORCE REGENERATE