Transparent Data Encryption (TDE) is a special case of encryption using a symmetric key. TDE encrypts entire database using a symmetric key called the database encryption key – DEK.
TDE does real-time I/O encryption and decryption of data and log files.
This encryption is known as encrypting data at rest. Introduced with SQL server 2008.

TDE isn't available for system databases. It can't be used to encrypt master, model, or msdb.
However, tempdb is automatically encrypted when a user database enabled TDE, but can't be encrypted directly.
TDE doesn't provide encryption across communication channels.

--Video link on how to encrypt a database backup
   • How to Encrypt a Database Backup in S...  


---SQL Script used in this video---
-- Encrypt a user database
--1.Create a Master key
use master
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'abc@123';

--2.Create a Certificate
CREATE CERTIFICATE democert WITH SUBJECT = 'my demo cert subject';

--3.Create a Database encryption key
use demo
CREATE DATABASE ENCRYPTION KEY
WITH ALGORITHM = AES_256
ENCRYPTION BY SERVER CERTIFICATE democert

--4.Backup the certificate and key
use master
BACKUP CERTIFICATE democert
TO FILE = 'F:\dbbackups\democert_cert.cer'
WITH PRIVATE KEY (FILE = 'F:\dbbackups\democert_key.key' , ENCRYPTION BY PASSWORD = 'abc@1123')

--5.Set encryption ON for the database
ALTER DATABASE demo set ENCRYPTION on

select name, database_id, is_encrypted
from sys.databases


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-- To restore a encrypted database --
restore database demo
from disk = 'F:\dbbackups\demo2.bak'

-- 1. Create a Master key
use master
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'xyz@123';

--2.Create a Certificate using the backup of source certificate & key

CREATE CERTIFICATE democert_pitr
FROM FILE = 'F:\dbbackups\democert_cert.cer'
WITH PRIVATE KEY (FILE = 'F:\dbbackups\democert_key.key',DECRYPTION BY PASSWORD = 'abc@1123')

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