chapter four

4 Authenticated encryption

 

This chapter covers:

  • Symmetric Encryption, a cryptographic primitive to hide communication from observers.
  • Authenticated Encryption, the secure evolution of symmetric encryption.
  • The popular authenticated encryption algorithms.
  • Other types of symmetric encryption.

Confidentiality is about hiding data from unwanted eyes, and authenticated encryption is the main way to achieve this. Encryption is what the science of cryptography was initially invented for, encryption is what pre-occupied most of the early cryptographers. "How can we prevent observers from understanding our conversations?" they would ask themselves. While the science and its advances first bloomed behind closed door, benefiting the governments and their military only, it has now opened and spread 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.

For this chapter you’ll need to have read:

  • Chapter 3 on message authentication codes.

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. in 2020

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

4.7 Summary