Sql Server Tde And Always Encrypted Complete Guide

SQL Server TDE (Transparent Data Encryption) and Always Encrypted: Explained in Detail with Important Information

Transparent Data Encryption (TDE)

Transparent Data Encryption (TDE) is designed to encrypt data at rest, protecting the entire database files, logs, and backups without requiring modifications to applications or code. TDE uses a database Encryption Key (DEK) to encrypt the data on disk and the DEK is protected by a Server Certificate or Asymmetric Key within the SQL Server Database Engine.

Key Features of TDE:

1. Ease of Use: TDE can be quickly enabled without major application changes.
2. Data at Rest Protection: Encrypts the entire database files (.mdf), logs (.ldf), and backup (.bak) files, making unauthorized access more difficult.
3. Performance Impact: Generally minimal; however, it may affect performance slightly, as encryption and decryption are handled by the database engine internally.

Implementation Steps:

1. Create a Master Key: This is essentially a secure password stored in the master database. It protects other encryption keys.

   CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'Strong@Passw0rd';
   

2. Create a Certificate: The certificate will be used to protect the Database Encryption Key (DEK).

   CREATE CERTIFICATE MyServerCertificate WITH SUBJECT = 'My Database Encryption Certificate';
   

3. Enable Database Encryption: Set up the DEK which is encrypted by the server certificate created above.

   USE YourDatabaseName;
   GO
   CREATE DATABASE ENCRYPTION KEY 
   WITH ALGORITHM = AES_256 
   ENCRYPTION BY SERVER CERTIFICATE MyServerCertificate;
   GO
   ALTER DATABASE YourDatabaseName
   SET ENCRYPTION ON;
   

4. Verify Encryption Status: Use the following query to check if TDE is active.

   SELECT name, is_encrypted FROM sys.databases
   WHERE name = 'YourDatabaseName';
   

Always Encrypted

Unlike TDE, Always Encrypted focuses on encrypting specific columns within the database rather than the whole database file. It ensures that the data is encrypted both at rest and in transit to and from the client applications. The encryption keys are never revealed to the SQL Server instance, making it highly secure against attacks.

Key Benefits of Always Encrypted:

1. Data in Transit and at Rest Security: Guarantees security even when data traverses network boundaries or rests unencrypted on SQL Server instances.
2. Client-Side Keys: Encryption and decryption happen client-side, not server-side, where the encryption keys stay outside of SQL Server's reach.
3. Fine-Grained Control: Allows for column-level security, enabling encryption only for sensitive data.

Implementation Steps:

1. Setting Up Column Master Key (CMK): This key resides in a separate environment and SQL Server does not have access to it. CMK can be stored in Windows Certificate Store, Azure Key Vault, etc.
2. Creating a Column Encryption Key (CEK): This key is used to encrypt individual columns of the table. It is encrypted with the CMK and stored in the database.
3. Enabling Encryption on Columns: Define the columns that need to be encrypted and set their encryption type.

SQL Code Example:

1. Create CMK:

   CREATE COLUMN MASTER KEY MyColumnMasterKey 
   WITH (
       KEY_STORE_PROVIDER_NAME = N'MSSQL_CERTIFICATE_STORE', 
       KEY_PATH = N'CurrentUser/My/A61A9C59FBDDF8E9D2AFAAE35BBDBB657D66D4F8'
   );
   

2. Create CEK:

   CREATE COLUMN ENCRYPTION KEY MyColumnEncryptionKey 
   WITH VALUES (
       COLUMN_MASTER_KEY = MyColumnMasterKey,
       ALGORITHM = 'AEAD_AES_256_CBC_HMAC_SHA_256',
       ENCRYPTED_VALUE = 0x016E000001630063...
   );
   

3. Enable Encryption:

   -- SSMS wizard creates script
   DECLARE @query NVARCHAR(MAX);
   DECLARE @columnsToEncrypt TABLE(
       NAME NVARCHAR(max),
       TYPE_NAME NVARCHAR(max)
   );
   INSERT INTO @columnsToEncrypt 
           (NAME,TYPE_NAME)
     VALUES
           ('SSN','NVARCHAR(11)'),
           ('CreditCardNumber','NVARCHAR(16)');
   
   WHILE (EXISTS(SELECT * FROM @columnsToEncrypt))
   BEGIN
      SELECT TOP 1 @query = N'ALTER TABLE [dbo].[Employees] 
                            ALTER COLUMN [' + Name + '] [' + TYPE_NAME + ']
                            COLLATE Latin1_General_BIN2
                            ENCRYPTED WITH (COLUMN_ENCRYPTION_KEY = [MyColumnEncryptionKey],
                                            ENCRYPTION_TYPE = Deterministic,
                                            ALGORITHM = ''AEAD_AES_256_CBC_HMAC_SHA_256'') '
      FROM @columnsToEncrypt;
   
      EXEC(@query);
   
      DELETE FROM @columnsToEncrypt
      WHERE Name=@name AND TYPE_NAME=@TYPE_NAME;
   END;
   

Important Considerations:

1. Maintenance Overhead:

   • TDE: Simpler maintenance since it encrypts the entire database. However, managing key rotation and revocation might be required.
   • Always Encrypted: Requires additional steps during setup, like managing CMK storage separately, and managing key rotation becomes complex with multiple keys.

2. Performance Impacts:

   • TDE: Typically has less performance impact as encryption/decryption happens internally.
   • Always Encrypted: Can introduce higher latency due to client-side encryption and decryption but is generally more secure.

3. Backup Concerns: – TDE: Encrypted backups; recovery also requires access to the server certificate/key. – Always Encrypted: Backups contain encrypted data within the specified columns. Recovery doesn’t require access to client-side keys.

4. Compliance:

   • Both TDE and Always Encrypted help achieve compliance requirements for protecting sensitive data. However, Always Encrypted might be more favorable for regulations mandating strict encryption and key management practices.

5. Security Best Practices:

   • Always keep encryption keys in a secure location and follow best practices for key management.
   • Regularly monitor and audit encryption activities.
   • Perform necessary key rotation periodically as per organizational policies.

By understanding these key differences and best practices, you can successfully implement TDE and Always Encrypted to enhance the security posture of your SQL Server databases, ensuring that sensitive information remains protected in compliance with regulatory standards.