The NetAcad modules, as cards you mark and drills that mark you.

Threats, Vulnerabilities & Attacks

Securing Networks

Attacking the Foundation

Attacking What We Do

Wireless Network Communication

Network Security Infrastructure

Linux Overview

System & Endpoint Protection

Cybersecurity Principles, Practices & Processes

Understanding Defense

System & Network Defense

Access Control

Access Control Lists

Cryptography

Algorithm Sorter

AES, RSA, DH, SHA-256, HMAC and the rest, one at a time: symmetric, asymmetric or hash. Harder rounds ask for key and digest sizes.

Which Key?

Confidentiality, authentication, signatures: pick whose key encrypts and whose decrypts. The public/private swap that costs the most marks.

Hash Lab

Hash text live and watch one character change the whole digest, then predict what salting, HMAC and a changed file do to the result.

Diffie-Hellman

Run the key exchange with small numbers: each side's public value, then the shared secret neither side ever sent. The arithmetic is marked.

Certificate Check

A certificate and its chain: trust it or not, and say why — expired, revoked, untrusted root, wrong name. CAs, CRL and OCSP in practice.

Recommend the Encryption

A situation, what it needs — confidentiality, integrity, origin authentication, non-repudiation — and the tool that delivers it. Every wrong option says why it fails.