Before I go on to the main body of this text, I would like to make a short digression about security in general.
Security is often in conflict with other interests in the programming trade. You have users screaming for a solution, and they want it now. At this point, they don’t really care about security, they just want to get their business done. But if you give them a solution that has a hole, and that hole is later exploited, you are the one that will be hung. So as a programmer you always need to have security in mind, and make sure that you play your part right
One common mistake in security is to think “we have this firewall/encryption/whatever, so we are safe”. I like to think of security of something that consists of a number of defence lines. Anyone who has worked with computer systems knows that there are a lot of changes in them, both in their configuration and in the program code. Your initial design may be sound and safe, but as the system evolves, there might suddenly be a security hole and a serious vulnerability in your system.
By having multiple lines of defence you can reduce the risk for this to happen. If a hole is opened, you can reduce the impact of what is possible to do through that hole. An integral part of this strategy is to never grant more permissions than is absolutely necessary. Exactly what this means in this context is something I shall return to.
This is a must-read for anyone interested in rights management in SQL Server.