Encrypt a Column of Data
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
In Object Explorer, connect to an instance of Database Engine.
On the Standard bar, select New Query.
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
In Object Explorer, connect to an instance of Database Engine.
On the Standard bar, select New Query.
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