Serious Cryptography, 2nd Edition

7 KEYED HASHING

The hash functions in Chapter 6 take a message and return its hash value—typically a short string of 256 or 512 bits. Anyone can compute the hash value of a message and verify that a particular message hashes to a particular value. When you want only specific people to compute hashes, however, you’ll hash with secret keys using keyed hash functions.

Keyed hashing forms the basis of two types of cryptographic algorithms: message authentication codes (MACs), which authenticate a message and protect its integrity, and pseudorandom functions (PRFs), which produce random-looking hash-sized values. We’ll look at the similarities ...