SQL Server encryption can be a complex topic to grasp, especially for those who are new to it. With so much information available, it can be overwhelming to understand the concepts and implementation. In this article, we will break down SQL Server encryption in a clear and understandable way.

The Simplest Approach

When it comes to SQL encryption, the goal is to encrypt columns of data. However, SQL Server does not provide an “encryption” attribute for columns. The simplest way to encrypt and decrypt data is by using the EncryptByPassphrase() and DecryptByPassPhrase() functions. However, this approach requires manually supplying the passphrase every time data needs to be encrypted or decrypted.

While this approach is straightforward, it is not the most secure or efficient method. Storing the passphrase inside a stored procedure is not recommended, as it can be easily compromised. Therefore, a better approach is needed.

A Better Approach

To overcome the passphrase problem, we can use the EncryptByKey() and DecryptByKey() functions. By encrypting our symmetric key “by certificate,” we eliminate the need for a passphrase. However, this approach requires creating a certificate and a master key.

First, we need to create the master key and certificate:

create master key encryption by password = 'SecretPassword';
create certificate MyCert with subject = 'MyCertSubj';

Once the certificate and master key are created, we can create the symmetric key:

create symmetric key MyKey with algorithm=AES_256 encryption by certificate MyCert;

With the key in place, we can now modify our data access code:

open symmetric key MyKey decryption by certificate MyCert;

-- Inserting encrypted data
insert MyTable(ClearText, EncryptedText) 
values (@s, EncryptByKey(Key_GUID('MyKey'), @s));

-- Selecting decrypted data
select ID, ClearText, cast(DecryptByKey(EncryptedText) as varchar(16)) as "Decrypted", EncryptedText 
from MyTable;

By using the DecryptByKeyAutoCert() function, we can simplify the decryption process and avoid the need to specify a password in our data access code.

Optimization – Indexing Encrypted Data

If we need to search for encrypted data, it is important to optimize the performance. Adding an extra indexed column containing a hashed version of the plaintext can improve query performance. However, it is crucial to use a hashing function that only applies to a subset of the plaintext to prevent dictionary attacks.

Moving Encrypted Data to Another Server – Disaster Recovery

When moving encrypted data to another server, it is essential to ensure that we can still decrypt it. The simplest way to achieve this is by synchronizing the service master keys on both servers. By backing up and restoring the service master key, we can maintain access to the encrypted data.

Proposed Approach

Based on the concepts discussed, here is a proposed approach for implementing data encryption in SQL Server 2005:

1. Create a master key and certificate.
2. Create a symmetric key with the desired encryption algorithm.
3. Create a DB role and grant access to the certificate and symmetric key.
4. If necessary, add an indexed column for encrypted data search optimization.
5. If data needs to be moved to another server, synchronize the service master keys.
6. Save all scripts in source control for future reference.

By following this approach, we can ensure secure and efficient data encryption in SQL Server 2005.

Remember, encryption is just one aspect of data security. It is important to consider other security measures, such as access control and secure network communication, to protect sensitive data.