I don't think you'll find a better group of books for $15, if your goal is to learn about security in general. Most of the stuff here is general crypto, which

I don't think you'll find a better group of books for $15, if your goal is to learn about security in general. Most of the stuff here is general crypto, which is very helpful with respect to just learning about computer security, though not necessarily focused on securing something like nginx specifically. You'll learn a lot more about security in general though, which will make it easier to learn about security specific platforms. I can't recommend this collection enough. I'd make the purchase, then dive into a couple and read whatever you find most interesting. I don't believe any will have the top keys of security technology X, Y, or Z. But you'll learn a lot in general, and it will be much easier to read other security how-tos and tutorials on locking down specific platforms.