In the selection process for database encryption solutions, too often the discussion devolves straight into the encryption technologies: the algorithms, computational complexity, key lengths, merits of public vs. private key cryptography, key management, and the like.

In the big picture, none of these topics matter.

While these nuances may be worth considering, that conversation sidesteps the primary business driver of the entire effort: what threat do you want to protect the data from? In this second post in our series on database encryption, we’ll provide a simple decision tree to guide you in selecting the right database encryption option based on the threat you’re trying to protect against. Once we’ve identified the business problem, we will then map that to the underlying technologies to achieve that goal. We think it’s safe to say that if you are looking at database encryption as an option, you have already come to the decision that you need to protect your data in some way. Since there’s always some expense and/or potential performance impact on the database, there must be some driving force to even consider encryption. We will also make the assumption that, at the very least, protecting data at rest is a concern. Let’s start the process by asking the following questions:

What do you want to protect? The entire contents of the database, a specific table, or a data field?

What do you want to protect the data from? Accidental disclosure? Data theft?

Once you understand these requirements, we can boil the decision process into the following diagram:

Whether your primary driver is security or compliance, the breakdown will be the same. If you need to provide separation of duties for Sarbanes-Oxley, or protect against account hijacking, or keep credit card data from being viewed for PCI compliance, you are worried about credentialed users. In this case you need a more granular approach to encryption and possibly external key management. In our model, we call this user encryption. If you are worried about missing tapes, physical server theft, copying/theft of the database files via storage compromise, or un-scrubbed hard drives being sold on eBay, the threat is outside of the bounds of access control. In these cases use of transparent/external encryption through native database methods, OS support, file/folder encryption, or disk drive encryption is appropriate.

Once you have decided which method is appropriate, we need to examine the basic technology variables that affect your database system and operations. Which you select corresponds to how much of an impact it will have on applications, database performance, and so on. With any form of database encryption there are many technology variables to consider for your deployment, but for the purpose of selecting which strategy is right for you, there are only three to worry about. These three effect the performance and type of threats you can address. In each case we will want to investigate if these options are performed internally by the database, or externally. They are:

  1. Where does the encryption engine reside? [inside/outside]
  2. Where is the key management performed? [inside/outside]
  3. Who/what performs the encryption operations? [inside/outside]

In a nutshell, the more secure you want to be and the more you need separation of duties, the more you will need granular enforcement and changes to your applications. Each option that is moved outside the database means you get more complexity and less application transparency. We hate to phrase it like this because it somehow implies that what the database provides is less secure when that is absolutely not the case. But it does mean that the more we manage inside the database, the greater the vulnerability in the event of a database or DBA account compromise. It’s called “putting all your eggs in one basket”. Throughout the remainder of the week we will discuss the major branches of this tree, and how they map to threats. We will follow that up with a set of use case discussions to contrast the models and set realistic expectations on security this will and will not provide, as well as some comments on the operational impact of using these technologies.

By the end you’ll be able to walk through our decision tree and pick the best encryption option based on what threat you’re trying to manage, and operational criteria ranging from what database platform you’re on to management requirements.