Understanding SQL Transparent Data Encryption (TDE)
What is SQL TDE? SQL Transparent Data Encryption (TDE) is a technology used in SQL Server and Azure SQL Database to perform real-time I/O encryption and decryption of the data and log files. TDE protects data “at rest”, meaning the data and log files are encrypted on the disk. The data within backups of those databases are also encrypted.
It is best practice to do this regardless of where the database is stored. In production environments, we are careful to ensure that users and staff have limited access to the databases, but what about our I.T. staff. It only takes one disgruntled staff member to access the data, log, or backup files, and then they can copy your valuable live data simply by copying those files – they can restore them anywhere.
This guide will explain how to set up and manage SQL encryption. So, even if data, logs or backup files are taken, the data within them cannot be accessed.
Setting Up SQL TDE
Prerequisites:
- SQL Server 2008 or later.
- Necessary permissions for creating keys and certificates.
Implementation Steps:
1. Create a Master Key:
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'YourStrongPassword';2. Create a Certificate Protected by the Master Key:
CREATE CERTIFICATE MyServerCert WITH SUBJECT = 'My DEK Certificate';3. Create a Database Encryption Key (DEK):
USE [YourDatabase];
CREATE DATABASE ENCRYPTION KEY WITH ALGORITHM = AES_256 ENCRYPTION BY SERVER CERTIFICATE MyServerCert;4. Enable Encryption on the Database
ALTER DATABASE [YourDatabase] SET ENCRYPTION ON;Managing Certificates for Disaster Recovery
Backup of Certificates:
It’s crucial to back up the certificate and private key used for TDE. Without it, you cannot restore a backup of your database!
Use the following command to back up the certificate and private key:
BACKUP CERTIFICATE MyServerCert TO FILE = 'C:\Backup\MyServerCert_Backup' WITH PRIVATE KEY (FILE = 'C:\Backup\MyServerCert_PrivateKey', ENCRYPTION BY PASSWORD ='YourBackupPassword');Store the backup in a secure, offsite location.
Restoring Certificates:
In a disaster, restoring the certificate is vital for accessing the encrypted database. Use the following command:
CREATE CERTIFICATE MyServerCert FROM FILE = 'C:\Backup\MyServerCert_Backup' WITH PRIVATE KEY (FILE = 'C:\Backup\MyServerCert_PrivateKey', DECRYPTION BY PASSWORD = 'YourBackupPassword');More SQL
The following code section regarding enabling TDE comes from Microsoft’s documentation site. It shows all of the above commands in a single flow: –
-- Create a database master key and a certificate in the master database.
USE master ;
GO
CREATE MASTER KEY ENCRYPTION BY PASSWORD = '*rt@40(FL&dasl1';
GO
CREATE CERTIFICATE TestSQLServerCert
WITH SUBJECT = 'Certificate to protect TDE key'
GO
-- Create a backup of the server certificate in the master database.
-- The following code stores the backup of the certificate and the private key file in the default data location for this instance of SQL Server
-- (C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA).
BACKUP CERTIFICATE TestSQLServerCert
TO FILE = 'TestSQLServerCert'
WITH PRIVATE KEY
(
FILE = 'SQLPrivateKeyFile',
ENCRYPTION BY PASSWORD = '*rt@40(FL&dasl1'
);
GO
-- Create a database to be protected by TDE.
CREATE DATABASE CustRecords ;
GO
-- Switch to the new database.
-- Create a database encryption key, that is protected by the server certificate in the master database.
-- Alter the new database to encrypt the database using TDE.
USE CustRecords;
GO
CREATE DATABASE ENCRYPTION KEY
WITH ALGORITHM = AES_128
ENCRYPTION BY SERVER CERTIFICATE TestSQLServerCert;
GO
ALTER DATABASE CustRecords
SET ENCRYPTION ON;
GOAutomating Certificate Management
- Automation of certificate backup can be achieved through SQL Server Agent Jobs or PowerShell scripts.
- Schedule regular backups to ensure you have the latest certificate and associated key backups.
Best Practices for TDE and Certificate Management
- Regularly rotate and update certificates and keys.
- Test the restoration process in a non-production environment to ensure you can recover your database in case of a disaster.
- Limit access to the certificate backups. Only authorized personnel should have access to these backups. Ideally, people with access to the certificate backups should not have access to the databases themselves. This means permissions from two people are needed to restore the database.
Conclusion: The Importance of TDE and Certificate Management
SQL TDE is a powerful tool for protecting data at rest. However, its effectiveness is contingent upon properly managing encryption keys and certificates. Regular backups, secure storage, and periodic backup and restore process testing are critical for disaster recovery planning.
For more information and detailed guides, visit Microsoft’s SQL Server documentation and engage with the SQL Server community for shared experiences and best practices.
