Symmetric and asymmetric encryption, hashing, public key infrastructure (PKI), and how TLS combines them.
Cryptography underpins nearly every other control in this program, from Module 5's authentication flows to Module 12's remote-access VPNs. This module covers the difference between symmetric encryption (one shared key, fast, hard to distribute) and asymmetric encryption (a public/private key pair, solves distribution at the cost of speed), why hashing is a deliberately one-way transformation used for integrity checks rather than confidentiality, and how a PKI certificate chain lets TLS combine both encryption types to secure a connection efficiently.
By the end of this module you should be able to explain, without hand-waving, why TLS uses asymmetric cryptography only to exchange a symmetric session key rather than encrypting the whole session asymmetrically — a distinction that resolves a surprising number of "why is this slow" and "why doesn't this scale" cryptography questions in practice.