Problem - Kevin Tafuro

Chapter 6 CHAPTER 6
Hashes and Message Authentication
In Chapter 5, we discussed primitives for symmetric encryption. Some of those primitives
were capable of providing two of the most important security goals: secrecy
and message integrity. There are occasions where secrecy may not be important in
the slightest, but you’d still like to ensure that messages are not modified as they go
over the Internet. In such cases, you can use a symmetric primitive such as CWC
mode, which allows you to authenticate data without encrypting any of it. Alternatively,
you can consider using a standalone message authentication code (MAC).
This chapter focuses on MACs, and it also covers two types of one-way hash functions:
cryptographic hash functions and “universal” hash functions. Cryptographic
hash functions are used in public key cryptography and are a popular component to
use in a MAC (you can also use block ciphers), but universal hash functions turn out
to be a much better foundation for a secure MAC.
Many of the recipes in this chapter are too low-level for general-purpose
use. We recommend that you first try to find what you need in
Chapter 9; the recipes there are more generally applicable. If you do
use these recipes, please be careful, read all our warnings, and consider
using the higher-level constructs we suggest.
6.1 Understanding the Basics of Hashes and
MACs
Problem
You would like to understand the basic concepts behind hash functions as used in
cryptography and message authentication codes (MACs).
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