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Encrypt a Column of Data

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Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics

This article describes how to encrypt a column of data by using symmetric encryption in SQL Server using Transact-SQL. This is sometimes known as column-level encryption, or cell-level encryption.

The Transact-SQL code samples in this article use the AdventureWorks2022 or AdventureWorksDW2022 sample database, which you can download from the Microsoft SQL Server Samples and Community Projects home page.

Security

Permissions

The following permissions are necessary to perform the steps below:

  • CONTROL permission on the database.
  • CREATE CERTIFICATE permission on the database. Only Windows logins, SQL Server logins, and application roles can own certificates. Groups and roles cannot own certificates.
  • ALTER permission on the table.
  • Some permission on the key and must not have been denied VIEW DEFINITION permission.

Create database master key

To use the following examples, you must have a database master key. If your database does not already have a database master key, create one. To create one, connect to your database and run the following script. Be sure to use a complex password.

Copy and paste the following example into the query window that is connected to the AdventureWorks sample database. Select Execute.

CREATE MASTER KEY ENCRYPTION BY   
PASSWORD = '<complex password>';

Always back up your database master key. For more information on database master keys, see CREATE MASTER KEY (Transact-SQL).

Example: Encrypt with symmetric encryption and authenticator

  1. In Object Explorer, connect to an instance of Database Engine.

  2. On the Standard bar, select New Query.

  3. Copy and paste the following example into the query window that is connected to the AdventureWorks sample database. Select Execute.

    CREATE CERTIFICATE Sales09  
   WITH SUBJECT = 'Customer Credit Card Numbers';  
GO  

CREATE SYMMETRIC KEY CreditCards_Key11  
    WITH ALGORITHM = AES_256  
    ENCRYPTION BY CERTIFICATE Sales09;  
GO  

-- Create a column in which to store the encrypted data.  
ALTER TABLE Sales.CreditCard   
    ADD CardNumber_Encrypted varbinary(160);   
GO  

-- Open the symmetric key with which to encrypt the data.  
OPEN SYMMETRIC KEY CreditCards_Key11  
   DECRYPTION BY CERTIFICATE Sales09;  

-- Encrypt the value in column CardNumber using the  
-- symmetric key CreditCards_Key11.  
-- Save the result in column CardNumber_Encrypted.    
UPDATE Sales.CreditCard  
SET CardNumber_Encrypted = EncryptByKey(Key_GUID('CreditCards_Key11')  
    , CardNumber, 1, HASHBYTES('SHA2_256', CONVERT( varbinary  
    , CreditCardID)));  
GO  

-- Verify the encryption.  
-- First, open the symmetric key with which to decrypt the data.  

OPEN SYMMETRIC KEY CreditCards_Key11  
   DECRYPTION BY CERTIFICATE Sales09;  
GO  

-- Now list the original card number, the encrypted card number,  
-- and the decrypted ciphertext. If the decryption worked,  
-- the original number will match the decrypted number.  

SELECT CardNumber, CardNumber_Encrypted   
    AS 'Encrypted card number', CONVERT(nvarchar,  
    DecryptByKey(CardNumber_Encrypted, 1 ,   
    HASHBYTES('SHA2_256', CONVERT(varbinary, CreditCardID))))  
    AS 'Decrypted card number' FROM Sales.CreditCard;  
GO

Encrypt with simple symmetric encryption

  1. In Object Explorer, connect to an instance of Database Engine.

  2. On the Standard bar, select New Query.

  3. Copy and paste the following example into the query window that is connected to the AdventureWorks sample database. Select Execute.

     CREATE CERTIFICATE HumanResources037  
   WITH SUBJECT = 'Employee Social Security Numbers';  
GO  

CREATE SYMMETRIC KEY SSN_Key_01  
    WITH ALGORITHM = AES_256  
    ENCRYPTION BY CERTIFICATE HumanResources037;  
GO  

USE [AdventureWorks2022];  
GO  

-- Create a column in which to store the encrypted data.  
ALTER TABLE HumanResources.Employee  
    ADD EncryptedNationalIDNumber varbinary(128);   
GO  

-- Open the symmetric key with which to encrypt the data.  
OPEN SYMMETRIC KEY SSN_Key_01  
   DECRYPTION BY CERTIFICATE HumanResources037;  

-- Encrypt the value in column NationalIDNumber with symmetric   
-- key SSN_Key_01. Save the result in column EncryptedNationalIDNumber.  
UPDATE HumanResources.Employee  
SET EncryptedNationalIDNumber = EncryptByKey(Key_GUID('SSN_Key_01'), NationalIDNumber);  
GO  

-- Verify the encryption.  
-- First, open the symmetric key with which to decrypt the data.  
OPEN SYMMETRIC KEY SSN_Key_01  
   DECRYPTION BY CERTIFICATE HumanResources037;  
GO  

-- Now list the original ID, the encrypted ID, and the   
-- decrypted ciphertext. If the decryption worked, the original  
-- and the decrypted ID will match.  
SELECT NationalIDNumber, EncryptedNationalIDNumber   
    AS 'Encrypted ID Number',  
    CONVERT(nvarchar, DecryptByKey(EncryptedNationalIDNumber))   
    AS 'Decrypted ID Number'  
    FROM HumanResources.Employee;  
GO

Next steps