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Use SQL Server Connector with SQL Encryption Features

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Applies to: SQL Server

Common SQL Server encryption activities using an asymmetric key protected by the Azure Key Vault include the following three areas.

  • Transparent Data Encryption by using an Asymmetric Key from Azure Key Vault

  • Encrypting Backups by Using an Asymmetric Key from the Key Vault

  • Column Level Encryption by Using an Asymmetric Key from the Key Vault

Complete parts I through IV of the topic Setup Steps for Extensible Key Management Using the Azure Key Vault, before following the steps on this topic.

Note

Versions 1.0.0.440 and older have been replaced and are no longer supported in production environments. Upgrade to version 1.0.1.0 or later by visiting the Microsoft Download Center and using the instructions on the SQL Server Connector Maintenance & Troubleshooting page under "Upgrade of SQL Server Connector."

Note

Microsoft Entra ID was previously known as Azure Active Directory (Azure AD).

Transparent Data Encryption by using an Asymmetric Key from Azure Key Vault

After completing Parts I through IV of the topic Setup Steps for Extensible Key Management Using the Azure Key Vault, use the Azure Key Vault key to encrypt the database encryption key using TDE. For more information about rotating keys using PowerShell, see Rotate the Transparent Data Encryption (TDE) protector using PowerShell.

Important

Do not delete previous versions of the key after a rollover. When keys are rolled over, some data is still encrypted with the previous keys, such as older database backups, backed-up log files and transaction log files.

You will need to create a credential and a login, and create a database encryption key which will encrypt the data and logs in the database. To encrypt a database requires CONTROL permission on the database. The following graphic shows the hierarchy of the encryption key when using the Azure Key Vault.

Diagram showing the hierarchy of the encryption key when using the Azure Key Vault.

  1. Create a SQL Server credential for the Database Engine to use for TDE

    The Database Engine uses the Microsoft Entra application credentials to access the Key Vault during database load. We recommend creating another Client ID and Secret, as described in Step 1, for the Database Engine, to limit the Key Vault permissions that are granted.

    Modify the Transact-SQL script below in the following ways:

    • Edit the IDENTITY argument (ContosoDevKeyVault) to point to your Azure Key Vault.

      • If you're using global Azure, replace the IDENTITY argument with the name of your Azure Key Vault from Part II.
      • If you're using a private Azure cloud (ex. Azure Government, Azure operated by 21Vianet, or Azure Germany), replace the IDENTITY argument with the Vault URI that is returned in Part II, step 3. Do not include "https://" in the Vault URI.

    • Replace the first part of the SECRET argument with the Microsoft Entra application Client ID from Step 1. In this example, the Client ID is EF5C8E094D2A4A769998D93440D8115D.

      Important

      You must remove the hyphens from the Client ID.

    • Complete the second part of the SECRET argument with Client Secret from Part I. In this example, the Client Secret from Part 1 is ReplaceWithAADClientSecret.

    • The final string for the SECRET argument will be a long sequence of letters and numbers, with no hyphens.

    USE master;  
CREATE CREDENTIAL Azure_EKM_TDE_cred   
    WITH IDENTITY = 'ContosoDevKeyVault', -- for global Azure
    -- WITH IDENTITY = 'ContosoDevKeyVault.vault.usgovcloudapi.net', -- for Azure Government
    -- WITH IDENTITY = 'ContosoDevKeyVault.vault.azure.cn', -- for Microsoft Azure operated by 21Vianet
    -- WITH IDENTITY = 'ContosoDevKeyVault.vault.microsoftazure.de', -- for Azure Germany   
    SECRET = 'EF5C8E094D2A4A769998D93440D8115DReplaceWithAADClientSecret'   
FOR CRYPTOGRAPHIC PROVIDER AzureKeyVault_EKM_Prov;

  2. Create a SQL Server login for the Database Engine for TDE

    Create a SQL Server login and add the credential from Step 1 to it. This Transact-SQL example uses the same key that was imported earlier.

    USE master;  
-- Create a SQL Server login associated with the asymmetric key   
-- for the Database engine to use when it loads a database   
-- encrypted by TDE.  
CREATE LOGIN TDE_Login   
FROM ASYMMETRIC KEY CONTOSO_KEY;  
GO   

-- Alter the TDE Login to add the credential for use by the   
-- Database Engine to access the key vault  
ALTER LOGIN TDE_Login   
ADD CREDENTIAL Azure_EKM_TDE_cred ;  
GO

  3. Create the Database Encryption Key (DEK)

    The DEK will encrypt your data and log files in the database instance, and in turn be encrypted by the Azure Key Vault asymmetric key. The DEK can be created using any SQL Server supported algorithm or key length.

    USE ContosoDatabase;  
GO  

CREATE DATABASE ENCRYPTION KEY   
WITH ALGORITHM = AES_256   
ENCRYPTION BY SERVER ASYMMETRIC KEY CONTOSO_KEY;  
GO

  4. Turn On TDE

    -- Alter the database to enable transparent data encryption.  
ALTER DATABASE ContosoDatabase   
SET ENCRYPTION ON;  
GO

    Using Management Studio, verify that TDE has been turned on by connecting to your database with Object Explorer. Right-click your database, point to Tasks, and then click Manage Database Encryption.

    Screenshot showing Object Explorer with Tasks > Manage Database Encryption selected.

    In the Manage Database Encryption dialog box, confirm that TDE is on, and what asymmetric key is encrypting the DEK.

    Screenshot of the Manage Database Encryption dialog box with the Set Database Encryption On option selected and a yellow banner that says Now TDE is turned on.

    Alternatively, you can execute the following Transact-SQL script. An encryption state of 3 indicates an encrypted database.

    USE MASTER  
SELECT * FROM sys.asymmetric_keys  

-- Check which databases are encrypted using TDE  
SELECT d.name, dek.encryption_state   
FROM sys.dm_database_encryption_keys AS dek  
JOIN sys.databases AS d  
     ON dek.database_id = d.database_id;

    Note

    The tempdb database is automatically encrypted whenever any database enables TDE.

Encrypting Backups by Using an Asymmetric Key from the Key Vault

Encrypted backups are supported starting with SQL Server 2014 (12.x). The following example creates and restores a backup encrypted a data encryption key protected by the asymmetric key in the key vault.
The Database Engine uses the Microsoft Entra application credentials to access the Key Vault during database load. We recommend creating another Client ID and Secret, as described in Step 1, for the Database Engine, to limit the Key Vault permissions that are granted.

  1. Create a SQL Server credential for the Database Engine to use for Backup Encryption

    Modify the Transact-SQL script below in the following ways:

    • Edit the IDENTITY argument (ContosoDevKeyVault) to point to your Azure Key Vault.

      • If you're using global Azure, replace the IDENTITY argument with the name of your Azure Key Vault from Part II.
      • If you're using a private Azure cloud (ex. Azure Government, Microsoft Azure operated by 21Vianet, or Azure Germany), replace the IDENTITY argument with the Vault URI that is returned in Part II, step 3. Do not include "https://" in the Vault URI.

    • Replace the first part of the SECRET argument with the Microsoft Entra application Client ID from Step 1. In this example, the Client ID is EF5C8E094D2A4A769998D93440D8115D.

      Important

      You must remove the hyphens from the Client ID.

    • Complete the second part of the SECRET argument with Client Secret from Part I. In this example the Client Secret from Part I is Replace-With-AAD-Client-Secret. The final string for the SECRET argument will be a long sequence of letters and numbers, with no hyphens.

      USE master;  

CREATE CREDENTIAL Azure_EKM_Backup_cred   
    WITH IDENTITY = 'ContosoDevKeyVault', -- for global Azure
    -- WITH IDENTITY = 'ContosoDevKeyVault.vault.usgovcloudapi.net', -- for Azure Government
    -- WITH IDENTITY = 'ContosoDevKeyVault.vault.azure.cn', -- for Microsoft Azure operated by 21Vianet
    -- WITH IDENTITY = 'ContosoDevKeyVault.vault.microsoftazure.de', -- for Azure Germany   
    SECRET = 'EF5C8E094D2A4A769998D93440D8115DReplace-With-AAD-Client-Secret'   
FOR CRYPTOGRAPHIC PROVIDER AzureKeyVault_EKM_Prov;

  2. Create a SQL Server login for the Database Engine for Backup Encryption

    Create a SQL Server login to be used by the Database Enginee for encryption backups, and add the credential from Step 1 to it. This Transact-SQL example uses the same key that was imported earlier.

    Important

    You cannot use the same asymmetric key for backup encryption if you've already used that key for TDE (the above example), or column level encryption (the following example).

    This example uses the CONTOSO_KEY_BACKUP asymmetric key stored in the key vault, which can be imported or created earlier for the master database, as Part IV, Step 5 earlier.

    USE master;  

-- Create a SQL Server login associated with the asymmetric key   
-- for the Database engine to use when it is encrypting the backup.  
CREATE LOGIN Backup_Login   
FROM ASYMMETRIC KEY CONTOSO_KEY_BACKUP;  
GO   

-- Alter the Encrypted Backup Login to add the credential for use by   
-- the Database Engine to access the key vault  
ALTER LOGIN Backup_Login   
ADD CREDENTIAL Azure_EKM_Backup_cred ;  
GO

  3. Backup the Database

    Backup the database specifying encryption with the asymmetric key stored in the key vault.

    In the below example, note that if the database was already encrypted with TDE, and the asymmetric key CONTOSO_KEY_BACKUP is different from the TDE asymmetric key, the backup will be encrypted by both the TDE asymmetric key and CONTOSO_KEY_BACKUP. The target SQL Server instance will need both keys in order to decrypt the backup.

    USE master;  

BACKUP DATABASE [DATABASE_TO_BACKUP]  
TO DISK = N'[PATH TO BACKUP FILE]'   
WITH FORMAT, INIT, SKIP, NOREWIND, NOUNLOAD,   
ENCRYPTION(ALGORITHM = AES_256,   
SERVER ASYMMETRIC KEY = [CONTOSO_KEY_BACKUP]);  
GO

  4. Restore the Database

    To restore a database backup that is encrypted with TDE, the target SQL Server instance must first have a copy of the asymmetric Key Vault key used for encryption. This is how this would be achieved:

    • If the original asymmetric key used for TDE is no longer in Key Vault, restore the Key Vault key backup or reimport the key from a local HSM. Important: In order to have the key's thumbprint match the thumbprint recorded on the database backup, the key must be named the same Key Vault key name as it was originally named before.

    • Apply Steps 1 and 2 on the target SQL Server instance.

    • Once the target SQL Server instance has access to the asymmetric key(s) used to encrypt the backup, restore the database on the server.

    Sample restore code:

    RESTORE DATABASE [DATABASE_TO_BACKUP]  
FROM DISK = N'[PATH TO BACKUP FILE]'   
    WITH FILE = 1, NOUNLOAD, REPLACE;  
GO

    For more information about backup options, see BACKUP (Transact-SQL).

Column Level Encryption by Using an Asymmetric Key from the Key Vault

The following example creates a symmetric key protected by the asymmetric key in the key vault. Then the symmetric key is used to encrypt data in the database.

Important

You cannot use the same asymmetric key for column level encryption if you've already used that key for backup encryption.

This example uses the CONTOSO_KEY_COLUMNS asymmetric key stored in the key vault, which can be imported or created earlier, as described in Step 3, section 3 of Setup Steps for Extensible Key Management Using the Azure Key Vault. To use this asymmetric key in the ContosoDatabase database, you must execute the CREATE ASYMMETRIC KEY statement again, to provide the ContosoDatabase database with a reference to the key.

USE [ContosoDatabase];  
GO  
  
-- Create a reference to the key in the key vault  
CREATE ASYMMETRIC KEY CONTOSO_KEY_COLUMNS   
FROM PROVIDER [AzureKeyVault_EKM_Prov]  
WITH PROVIDER_KEY_NAME = 'ContosoDevRSAKey2',  
CREATION_DISPOSITION = OPEN_EXISTING;  
  
-- Create the data encryption key.  
-- The data encryption key can be created using any SQL Server   
-- supported algorithm or key length.  
-- The DEK will be protected by the asymmetric key in the key vault  
  
CREATE SYMMETRIC KEY DATA_ENCRYPTION_KEY  
    WITH ALGORITHM=AES_256  
    ENCRYPTION BY ASYMMETRIC KEY CONTOSO_KEY_COLUMNS;  
  
DECLARE @DATA VARBINARY(MAX);  
  
--Open the symmetric key for use in this session  
OPEN SYMMETRIC KEY DATA_ENCRYPTION_KEY   
DECRYPTION BY ASYMMETRIC KEY CONTOSO_KEY_COLUMNS;  
  
--Encrypt syntax  
SELECT @DATA = ENCRYPTBYKEY  
    (  
    KEY_GUID('DATA_ENCRYPTION_KEY'),   
    CONVERT(VARBINARY,'Plain text data to encrypt')  
    );  
  
-- Decrypt syntax  
SELECT CONVERT(VARCHAR, DECRYPTBYKEY(@DATA));  
  
--Close the symmetric key  
CLOSE SYMMETRIC KEY DATA_ENCRYPTION_KEY;

See Also

Setup Steps for Extensible Key Management Using the Azure Key Vault
Extensible Key Management Using Azure Key Vault
EKM provider enabled Server Configuration Option
SQL Server Connector Maintenance & Troubleshooting