Is it worth encrypting email addresses in the database?

Bruce Schneier has a good response to this kind of problem.

Cryptography is not the solution to your security problems. It might be part of the solution, or it might be part of the problem. In many situations, cryptography starts out by making the problem worse, and it isn't at all clear that using cryptography is an improvement.

Essentially encrypting your emails in the database 'just in case' is not really making the database more secure. Where are the keys stored for the database? What file permissions are used for these keys? Is the database accesable publically? Why? What kind of account restrictions are in place for these accounts? Where is the machine stored, who has physical access to this box? What about remote login/ssh access etc. etc. etc.

So I guess you can encrypt the emails if you want, but if that is the extent of the security of the system then it really isn't doing much, and would actually make the job of maintaining the database harder.

Of course this could be part of an extensive security policy for your system - if so then great!

I'm not saying that it is a bad idea - But why have a lock on the door from Deadlocks'R'us which cost $5000 when they can cut through the plywood around the door? Or come in through the window which you left open? Or even worse they find the key which was left under the doormat. Security of a system is only as good as the weakest link. If they have root access then they can pretty much do what they want.

Steve Morgan makes a good point that even if they cannot understand the email addresses, they can still do a lot of harm (which could be mitigated if they only had SELECT access)

Its also important to know what your reasons are for storing the email address at all. I might have gone a bit overboard with this answer, but my point is do you really need to store an email address for an account? The most secure data is data that doesn't exist.

I realize this is a dead topic, but I agree with Arjan's logic behind this. There are a few things I'd like to point out:

Someone can retrieve data from your database without retrieving your source code (i.e. SQL injection, third-party db's). With this in mind, it's reasonable to consider using an encryption with a key. Albeit, this is only an added measure of security, not the security...this is for someone who wants to keep the email more private than plaintext, In the off chance something is overlooked during an update, or an attacker manages to retrieve the emails.

IMO: If you plan on encrypting an email, store a salted hash of it as well. Then you can use the hash for validation, and spare the overhead of constantly using encryption to find a massive string of data. Then have a separate private function to retrieve and decrypt your emails when you need to use one.

In common with most security requirements, you need to understand the level of threat.

What damage can be done if the email addresses are compromised?

What's the chance of it happening?

The damage done if email addresses are REPLACED could be much greater than if they're EXPOSED. Especially if you're, for example, using the email address to verify password resets to a secure system.

The chance of the passwords being either replaced or exposed is much reduced if you hash them, but it depends what other controls you have in place.