V4b: CBC-MAC and HMAC (Applied Cryptography 101)

Welcome to this video on Message Authentication Codes (MACs), a critical topic in cryptography from Alfred Menezes's "Crypto 101: Building Blocks" course. In this lecture, we cover various MAC schemes that ensure data integrity and authenticity in cryptographic protocols. We start by introducing the basic concept of MACs, which use a secret key to generate a tag or code to authenticate messages. We then dive into the CBC-MAC (Cipher Block Chaining Message Authentication Code) and explain how it uses block ciphers to create a secure MAC. We discuss the potential vulnerabilities of CBC-MAC and its limitations in ensuring security when the message length is not fixed. Next, we explore EMAC (Encrypting Message Authentication Code), an alternative that overcomes some of CBC-MAC’s drawbacks, providing better security for variable-length messages. One of the most widely-used MAC schemes is HMAC (Hashed Message Authentication Code), which combines a cryptographic hash function with a secret key to produce an authentication tag. We also cover key derivation functions (KDFs), which are used in various cryptographic protocols to derive secret keys securely from passwords or other inputs. By the end of this video, you will understand the importance and implementation of different MAC schemes, including HMAC and KDFs, in securing communications. Lecture playlist: https://www.youtube.com/playlist?list=PLA1qgQLL41SRsHMtsb4up5fTytDeHV_yJ Course web page: https://cryptography101.ca/crypto101-building-blocks/ The slides are available on the course web page. Other cryptography courses: https://cryptography101.ca Slides 00:00 Introduction 00:16 Slide 176: MACs based on block ciphers 01:34 Slide 177: Security of CBC-MAC 02:25 Slide 178: Security of CBC-MAC (2) 03:59 Slide 179: Encrypted CBC-MAC (EMAC) 04:58 Slide 180: MACs based on hash functions 06:13 Slide 181: Secret prefix method 07:40 Slide 182: Length extension attack on secret-prefix MAC 08:19 Slide 183: HMAC 10:07 Slide 184: HMAC (2) 11:29 Slide 185: Key derivation functions 13:09 Coming up Corrections: 07:58 Slide 182: I said "by compressing t and f" when I should have said "by compressing t and y". The slide is correct.