Learn how to secure networks, applications, and systems against digital threats.
Cybersecurity is the practice of protecting systems, networks, and data from harm. At its core it is a way of thinking: what are we protecting, from whom, and what happens if we fail. Every more advanced security topic — cryptography, network security, penetration testing — builds on a small set of foundational ideas. This lesson introduces those ideas: the CIA Triad, the difference between authentication and authorization, assets, threats, vulnerabilities, and risk, security controls, and how to think about threats systematically with the STRIDE threat-modeling framework. By the end you will be able to look at a system and reason about what could go wrong, how likely it is, and what you can do about it.
Cybersecurity protects information and the systems that store, process, and transmit it. It is not just technology — it is also people and process.
CIA is the classic model for what security protects. It stands for Confidentiality, Integrity, and Availability.
| Property | Meaning | Example of a failure |
|---|---|---|
| Confidentiality | Only authorized people can read the data | A leaked database of customer records |
| Integrity | Data is not altered without authorization | An attacker changes an account balance |
| Availability | Data and services are reachable when needed | A denial-of-service attack takes a site offline |
These are often confused but are different. Authentication answers "who are you?"; authorization answers "what are you allowed to do?".
Risk combines likelihood and impact. You cannot eliminate all risk; security is about reducing it to an acceptable level, focusing effort where harm would be greatest.
| Type | Question it answers | Example |
|---|---|---|
| Preventive | Stop the incident | Firewall, strong password policy |
| Detective | Notice the incident | Logging, intrusion detection |
| Corrective | Fix the incident | Backup restore, patching |
Threat modeling is a structured way to find and prioritise threats. STRIDE is a mnemonic for six categories of threat.
| STRIDE | Threat |
|---|---|
| Spoofing | Pretending to be someone else |
| Tampering | Modifying data or code |
| Repudiation | Denying you did something |
| Information Disclosure | Exposing data to the wrong people |
| Denial of Service | Making a service unavailable |
| Elevation of Privilege | Gaining higher access than intended |
A threat uses an exploit to take advantage of a vulnerability, producing impact. Reducing any link in this chain reduces risk.
Defense in depth layers multiple controls so that if one fails, others still protect. No single control is sufficient.
For a login form, think through STRIDE: Spoofing (stolen credentials), Tampering (modify a request), Information Disclosure (expose user data), Denial of Service (flood the endpoint).
(each threat maps to a mitigation)