You are now entering the second part of this book, which is going to make use of most of what you’ve learned in the first part. Think about it this way: if the cryptographic primitives you’ve learned about were the basic ingredients of cryptography, you’re now about to learn some recipes. And there’s a lot to cook! While Caesar might have only been interested in encrypting his communications, today cryptography is all over the place, and it’s quite hard to keep track of it all.
In chapter 9, 10, and 11, I show you where you are most likely to run into cryptography and how cryptography is used to solve real-world problems; that is, how cryptography encrypts communications and how it authenticates participants in protocols. For the most part, that’s what cryptography is about. Participants will be numerous or few, and made of bits or flesh. As you’ll quickly realize, real-world cryptography is about tradeoffs and, based on the context, solutions will differ.