Column-level encryption in SQL Server

 Column-level encryption in SQL Server provides encryption at the column level, allowing you to protect sensitive data within specific columns of a table. This method offers more granular control over data encryption compared to Transparent Data Encryption (TDE).

Steps to Implement Column-Level Encryption

Step 1: Create a Master Key

The master key is required to encrypt the certificate used for the database encryption key.

USE master;
GO
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'YourStrongPassword';
GO

Step 2: Create a Certificate

Create a certificate in the master database to encrypt the symmetric key.

CREATE CERTIFICATE ColumnEncryptionCert
WITH SUBJECT = 'Column Encryption Certificate';
GO

Step 3: Create a Symmetric Key

Create a symmetric key that will be used to encrypt and decrypt the data in the column.

USE YourDatabase; -- Replace with your database name
GO
CREATE SYMMETRIC KEY ColumnEncryptionKey
WITH ALGORITHM = AES_256
ENCRYPTION BY CERTIFICATE ColumnEncryptionCert;
GO

Step 4: Encrypt Data in the Column

Encrypt the data in the specific column using the symmetric key.

-- Open the symmetric key
OPEN SYMMETRIC KEY ColumnEncryptionKey
DECRYPTION BY CERTIFICATE ColumnEncryptionCert;

-- Encrypt data and insert it into the table
INSERT INTO YourTable (ID, EncryptedColumn)
VALUES (1, EncryptByKey(Key_GUID('ColumnEncryptionKey'), 'Sensitive Data'));
GO

-- Close the symmetric key
CLOSE SYMMETRIC KEY ColumnEncryptionKey;
GO

Step 5: Decrypt Data from the Column

To retrieve and decrypt the encrypted data, you need to open the symmetric key and use the DecryptByKey function.

-- Open the symmetric key
OPEN SYMMETRIC KEY ColumnEncryptionKey
DECRYPTION BY CERTIFICATE ColumnEncryptionCert;

-- Select and decrypt the data
SELECT ID, CONVERT(VARCHAR, DecryptByKey(EncryptedColumn)) AS DecryptedData
FROM YourTable;
GO

-- Close the symmetric key
CLOSE SYMMETRIC KEY ColumnEncryptionKey;
GO

Full Example Script

Here is the full script combining all the steps:

-- Step 1: Create a Master Key
USE master;
GO
CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'YourStrongPassword';
GO

-- Step 2: Create a Certificate
CREATE CERTIFICATE ColumnEncryptionCert
WITH SUBJECT = 'Column Encryption Certificate';
GO

-- Step 3: Create a Symmetric Key
USE YourDatabase; -- Replace with your database name
GO
CREATE SYMMETRIC KEY ColumnEncryptionKey
WITH ALGORITHM = AES_256
ENCRYPTION BY CERTIFICATE ColumnEncryptionCert;
GO

-- Step 4: Encrypt Data in the Column
-- Create a table for demonstration
CREATE TABLE YourTable (
    ID INT PRIMARY KEY,
    EncryptedColumn VARBINARY(MAX)
);
GO

-- Open the symmetric key
OPEN SYMMETRIC KEY ColumnEncryptionKey
DECRYPTION BY CERTIFICATE ColumnEncryptionCert;

-- Encrypt data and insert it into the table
INSERT INTO YourTable (ID, EncryptedColumn)
VALUES (1, EncryptByKey(Key_GUID('ColumnEncryptionKey'), 'Sensitive Data'));
GO

-- Close the symmetric key
CLOSE SYMMETRIC KEY ColumnEncryptionKey;
GO

-- Step 5: Decrypt Data from the Column
-- Open the symmetric key
OPEN SYMMETRIC KEY ColumnEncryptionKey
DECRYPTION BY CERTIFICATE ColumnEncryptionCert;

-- Select and decrypt the data
SELECT ID, CONVERT(VARCHAR, DecryptByKey(EncryptedColumn)) AS DecryptedData
FROM YourTable;
GO

-- Close the symmetric key
CLOSE SYMMETRIC KEY ColumnEncryptionKey;
GO

Additional Considerations

• Key Management: Properly manage and store encryption keys and certificates. Losing access to these keys means you cannot decrypt the data.
• Performance: Column-level encryption can have an impact on performance, especially with large datasets. Use it judiciously for sensitive data that needs protection.
• Data Types: Ensure that the data types of the columns to be encrypted are compatible with encryption and decryption functions.

By following these steps, you can implement column-level encryption in SQL Server, providing enhanced security for sensitive data within specific columns of your database tables.

Transparent Data Encryption (TDE)
Column-Level Encryption
Always Encrypted
Dynamic Data Masking (DDM)
Transport Layer Security (TLS)