1. Introduction

Greetings traveler,

Sit tight as you’re about to enter a world of wonder and mystery—the world of cryptography. Cryptography is the ancient discipline of securing situations that are troubled with malicious characters. In this book are the spells we need to defend ourselves against the malice. Many have attempted to learn this craft, but few have survived the challenges that stand in the way of mastery. Exciting adventures await! We’ll uncover how cryptographic algorithms can secure our letters, identify our allies, and protect treasures from our enemies. Sailing through the cryptographic sea will not be the smoothest journey, as cryptography is the foundation of all security in our world, the slightest mistake could be deadly.

1.1 Cryptography is about securing protocols

Our journey starts here with an introduction to cryptography, the science aiming to defend protocols against saboteurs. But first, what’s a protocol? Simply put: it’s a list of steps that one (or more people) must follow in order to achieve something. For example, imagine the following premise: you want to leave your magic sword unattended for a few hours so you can take a nap. One protocol to do this could be the following:

1.2 Symmetric cryptography: what is symmetric encryption?

1.3 Kerckhoff’s principle: only the key is kept secret

1.4 Asymmetric cryptography: two keys are better than one

1.4.1 Key exchanges, or how to get a shared secret

1.4.2 Asymmetric encryption, not like the symmetric one

1.4.3 Digital signatures, just like your pen-and-paper signatures

1.5 Classifying and abstracting cryptography

1.6 Theoretical cryptography versus real-world cryptography

1.7 From theoretical to practical: choose your own adventure

1.8 A word of warning

1.9 Summary