4 Authenticated encryption

Confidentiality is about hiding data from unwanted eyes and encryption is the way to achieve this. Encryption is what the science of cryptography was initially invented for; it’s what preoccupied most of the early cryptographers. They would ask themselves, “How can we prevent observers from understanding our conversations?” While the science and its advances first bloomed behind closed doors, benefiting the governments and their militaries only, it is now opened throughout the world. Today, encryption is used everywhere to add privacy and security in the different aspects of our modern lives. In this chapter, we’ll find out what encryption really is, what types of problems it solves, and how today’s applications make heavy use of this cryptographic primitive.

4.1 What’s a cipher?

It’s like when you use slang to talk to your siblings about what you’ll do after school so your mom doesn’t know what you’re up to.

—Natanael L. (2020, https://twitter.com/Natanael_L)

4.2 The Advanced Encryption Standard (AES) block cipher

4.2.1 How much security does AES provide?

4.2.2 The interface of AES

4.2.3 The internals of AES

4.3 The encrypted penguin and the CBC mode of operation

4.4 A lack of authenticity, hence AES-CBC-HMAC

4.5 All-in-one constructions: Authenticated encryption

4.5.1 What’s authenticated encryption with associated data (AEAD)?

4.5.2 The AES-GCM AEAD

4.5.3 ChaCha20-Poly1305

4.6 Other kinds of symmetric encryption

4.6.1 Key wrapping