Recently I have been having quite a few discussions around security of data inside of SQL Server and how to prevent the massive data breaches that we have been hearing about on the news.  Like most things some people want “THE ANSWER” or THE SOLUTION to securing the data inside of SQL Server. Unfortunately there isn’t a single solution that solves all of the problems that are potentially out there.  Security of data requires defense in depth, starting with a secure configuration and installation of SQL Server.  Often times, defense in depth also means changes to the database, the application, and how you do business.

Features for Securing Data

SQL Server offers multiple options and features that help with securing data and since SQL Server 2016 Service Pack 1, many of them are available in Standard Edition:

  • SSL/TLS Protocol Encryption

    • SQL Server 2005+
    • Uses a SSL certificate to encrypt the network connection between clients and SQL Server, securing data from watching over the wire
    • Can be forced by SQL Server during the handshake when certificate properly installed on SQL Server certificate store
    • Only requires a SSL certificate from a CA for Server Authentication to implement
    • Requires certificate rotation before expiration
    • Generally does not require application changes but may under specific conditions
  • Database Column Level Encryption

    • SQL Server 2005+
    • Uses a certificate or key to encrypt a column securing data from being queried without knowing how to decrypt the values
    • Data remains encrypted at the column level even while the database is online
    • Encryption keys are maintained inside of the SQL Server encryption hierarchy and must be opened properly to decrypt data
    • May require application changes to support encryption
      • Not required if handled by stored procedure access to data but opens risks of decrypted data in process memory
    • Performance impacts when comparing column data in WHERE clause
      • May be mitigated by encrypting value to compare first and performing binary filtering of encrypted values
  • Transparent Data Encryption

    • SQL Server 2012+
    • Encrypts data at rest using database encryption key stored in the boot record of the database and a certificate stored in master
    • Prevents someone copying files or stealing a database backup from restoring the data without the certificate
    • Does not require application changes for securing data at rest
    • Does not protect data from being queried through SQL Server once the database is open
    • If someone has access to the master database or a backup of master, they can get the certificate that encrypts other backups (https://simonmcauliffe.com/technology/tde/)
    • Without the certificate that encrypts the database you cannot recover from a disaster
    • Certificate expiration is not enforced or checked and does not require certificate rotation once used for encryption
  • Backup Encryption

    • SQL Server 2014+
    • Encrypts the backup file using a certificate or asymmetric key, securing data backups from being restored
    • Prevents someone stealing a database backup from restoring the data without the certificate or key
    • Same potential risks as TDE since certificate or key is stored in the master database
  • Always Encrypted

    • SQL Server 2016+
    • Data remains encrypted at the column level even while the database is online
    • Column encryption keys are stored in the database to encrypt data
    • Column master keys are used to encrypt the column encryption keys in the database and are maintained outside of SQL Server and are not available to the DB, securing data from DBAs
      • Requires installing column master keys for SSMS to query and decrypt data – Windows Certificate Store, Azure Key Vault, or HSM
    • Requires application changes to support the encryption
    • Protects data in use from memory dumps and maintains encryption

How do we apply this for Securing Data?

Generally speaking, the first thing that we need to define is what specifically we are trying to protect against?  If we need to prevent someone from monitoring  or intercepting network packets containing data in clear text then we need to implement protocol encryption for connections.  If we are concerned about someone opening the database on another system or stealing a copy of the database or backups using TDE might be a good solution, but only if we also maintain a defense in depth strategy that separates our backups of master and the certificates used by TDE from the database backup files.  If we don’t separate our backups then TDE is very easy to hack around and is simply checking the box without actually securing our data.  If we want to protect the data at rest and from prying eyes while open, then we need to implement some form of column level encryption of the data, whether that is key based inside of SQL Server or using Always Encrypted. The important thing is that there isn’t a single solution that is going to protect every situation, you have to consider the risks and what a specific feature is designed to protect against and then layer them together to meet the requirements. Even then you might not be protected.

Take as an example, the Microsoft Customer Support Database data exposure that happened December 2019 and Microsoft provided public information about after securing the data.  While we don’t know all the security measures that were in place specifically on the database level, none of the above features would have protected the data from being publicly viewable through an application level security misconfiguration. As a part of any data security discussion, auditing and regular reviews of business practices, and any changes, have to be implemented to ensure that the data remains secured.