Everything here is open. Lessons are ordered, but nothing is locked, read in order if you're starting out, or jump straight to what you need.
The mental model and the moving parts: how to think about security, and how a single web request travels from your browser to a server and back.
The core ideas every later lesson builds on: the CIA triad, identity, and how attacks unfold.
Trace one page load end to end, and learn the addressing underneath it.
The languages machines speak, the doors they listen on, and how attackers target people.
Get fluent at the Linux shell every tool runs on, then understand how networks are built, divided, and defended.
Hands-on shell skills: navigating files, permissions, processes, and network commands.
How traffic is routed, how networks are segmented, and how firewalls hold the line.
Reconnaissance and port scanning: mapping networks and identifying attack surface with nmap.
Administer a server the real way: SSH login and hardening, scp/sftp transfers, tunnels, and FTP.
Open up encrypted connections and the packets on the wire: how TLS and certificates build trust, and how to read traffic with Wireshark-style filters.
What the padlock really means: the TLS handshake and the chain of trust behind it.
Capture, read, and filter packets in an in-browser Packet Lab, no install required.