Summary

In this chapter, we learned what MACs are and how they differ from message digests and digital signatures. We also learned about MAC function security and attacks that a good MAC function must resist. Following this, we learned what an HMAC function is and what its security depends on. We finished the theoretical part with a review of several methods of combining a MAC function with encryption, discovered what the best method is, and discussed the Cryptographic Doom Principle.

In the practical part, we learned about two methods of HMAC calculation on the command line. Then, we also learned how to calculate HMAC programmatically in C code. We compared the resulting HMACs calculated by all the methods used and, to our satisfaction, confirmed that all the methods produced the same HMAC.

In the next chapter, we will learn about Key Derivation Functions (KDFs) and how to derive encryption keys from passwords.