Before you start

This course starts from zero. Here are the words the other lessons lean on, so nothing comes out of nowhere.

A computer runs an operating system (OS), like Windows, macOS, Linux, Android or iOS, which runs your programs and decides who may open which files. Each person signs in to an account. An admin account (called root on Linux) can change anything on the machine, which is why attackers want one.

Computers talk over a network. Each device has an IP address, like 192.0.2.10, and data travels in small pieces called packets. A server is a computer that offers something to others (a website, email, files); a client is the one asking, like your browser. A port is a number that says which program on a server should get the data: 443 for secure websites (HTTPS), 22 for SSH (a secure command line on another computer), 25 for email between servers. The internet is many networks joined by routers, which pass packets along.

Software is written in code, and code has bugs. A bug that lets someone do something they shouldn't is a vulnerability. A patch (an update) fixes it. Much of security is keeping things patched and noticing when someone tries to use a hole that isn't fixed yet.

Encryption scrambles data with a key so only someone with the right key can read it. A hash turns any data into a short fixed-length fingerprint that can't be turned back. Both get their own lesson; for now, just the words.

Some lessons show a few lines of Python with what they print. You don't need to write any. print(x) shows a value. Text goes in quotes, like "hello". A line starting # is a note for people, ignored by the computer. import hashlib loads a built-in toolbox, and hashlib.sha256(...) uses a tool from it. def name(...): makes a small reusable function, and its indented lines are what it does.

# a note, ignored
name = "duck"            # a variable holds a value
print(name.upper())       # .upper() makes capitals
print(len(name))          # len() counts characters