Year 9 Digital Technologies · Digital Systems · 18m read

Networked Systems and Cybersecurity

Ever wonder what actually happens when you hit send on a message or log into your bank account? Your data zooms through connected computers and devices that all work together to get it where it needs to go, but it also needs protection from people trying to steal it. Learning how networks function and what keeps your information safe is crucial for protecting yourself online and for any tech-related career you might pursue.

Learning objective: Explain how hardware and software manage and secure data in networked systems.

By the end of this lesson you can:

I can describe how a network transmits data.
I can explain common cybersecurity threats and defences.
I can apply security principles to protect personal data.

A network is a city with walls. Roads (cables, Wi-Fi) connect buildings (devices); gates (firewalls) and guards (passwords) keep intruders out.

How networks work and stay secure

NETWORKS:
• A network connects devices to share resources and information.
• LAN (Local Area Network) — home or school network.
• WAN (Wide Area Network) — the internet (connects LANs globally).
• PROTOCOL: agreed rules for communication. HTTP/HTTPS, FTP, SMTP.
• IP ADDRESS: unique identifier for every device on a network (like a postal address).
• DNS (Domain Name System): translates "www.example.com" into an IP address.
• PACKET SWITCHING: data broken into packets, routed independently, reassembled.

HARDWARE:
• ROUTER: directs packets between networks.
• SWITCH: connects devices within a LAN.
• FIREWALL: filters traffic — blocks unauthorised access.
• SERVER: provides services to other devices (web, email, file storage).
• ACCESS POINT: provides wireless connectivity (Wi-Fi) to a wired network.
• MODEM: converts signal from ISP (Internet Service Provider) for home use.

### Network Models

OSI MODEL (7 layers — remember "All People Seem To Need Data Processing"):
Layer 7 Application — what the user sees (HTTP, email)
Layer 4 Transport — end-to-end delivery (TCP, UDP)
Layer 3 Network — addressing and routing (IP)
Layer 2 Data Link — node-to-node (MAC addresses)
Layer 1 Physical — cables, Wi-Fi signals

TCP vs UDP:
| Feature | TCP | UDP |
|---------|-----|-----|
| Reliability | Guaranteed delivery | Best effort, no guarantee |
| Speed | Slower (handshaking) | Faster |
| Use case | Web, email, file transfer | Video streaming, gaming, DNS |

CYBERSECURITY THREATS:
• PHISHING: fake emails/sites to steal credentials.
• MALWARE: malicious software (viruses, ransomware, spyware, Trojans).
• MAN-IN-THE-MIDDLE: attacker intercepts communication between two parties.
• DDoS (Distributed Denial of Service): flooding a server to knock it offline.
• SOCIAL ENGINEERING: manipulating humans, not systems.
• SQL INJECTION: inserting malicious SQL code into a web form to extract database data.
• ZERO-DAY EXPLOIT: attack targeting a vulnerability unknown to the vendor.

### Australian Context

Australia's ASD (Australian Signals Directorate) publishes the "Essential Eight" — a set of mitigation strategies:
1. Application control 2. Patch applications 3. Configure Office macros
4. User application hardening 5. Restrict admin privileges 6. Patch operating systems
7. Multi-factor authentication 8. Regular backups

DEFENCES:
• ENCRYPTION: converts data to unreadable cipher text (HTTPS, TLS).
• STRONG PASSWORDS + MFA: multi-factor authentication.
• REGULAR UPDATES: patch known vulnerabilities.
• FIREWALL and ANTIVIRUS.
• BACKUPS: ransomware protection.
• USER EDUCATION: the "human firewall."
• NETWORK SEGMENTATION: isolate sensitive systems so an infection can't spread freely.
• PRINCIPLE OF LEAST PRIVILEGE: users only get access they actually need.

AARI TIP: Ask Aari to explain how HTTPS protects your data and what happens when you click a phishing link.

Network security basics

Encryption: HTTPS scrambles your data so eavesdroppers can't read it.
MFA: Second factor (code on phone) stops password theft alone.
Updates: Most attacks exploit known vulnerabilities in unpatched software.

Worked example (Medium)

A school's network is hit by ransomware. Trace how this might have happened and what protections could have prevented it.

Attack vector. A teacher opened a phishing email attachment labelled "unpaid invoice.pdf" — it installed ransomware.
Spread. Ransomware spread across the network, encrypting files on shared drives.
Demand. Attackers demanded payment (in cryptocurrency) for the decryption key.
Preventions. (1) Email filtering to block suspicious attachments. (2) MFA on all accounts. (3) Network segmentation to stop lateral spread. (4) Regular offline backups — restore without paying ransom.

Answer: Most ransomware attacks succeed through human error + inadequate technical controls. Multiple layers of defence are required.

Common mistakes

Saying "a firewall stops all hackers" Firewalls filter network traffic but cannot prevent phishing, social engineering, or insider threats Fix: Explain that defence-in-depth requires multiple layers: technical controls AND user education
Confusing encryption with password protection Passwords restrict access; encryption scrambles the actual data so interceptors can't read it even if they capture it Fix: HTTPS encrypts the data in transit; a password is just the key to unlock access
Thinking HTTPS means a website is safe/legitimate HTTPS only means the connection is encrypted — a phishing site can also use HTTPS Fix: HTTPS = encrypted connection; it says nothing about whether the site itself is trustworthy

Worked example (Hard)

A bank discovers that customer login credentials are being stolen despite HTTPS being in use. Investigate possible attack vectors and recommend a layered defence strategy.

Rule out simple cases. HTTPS encrypts the channel, so a passive eavesdropper cannot intercept credentials in transit. The breach must be occurring elsewhere.
Possible attack vectors. (1) PHISHING: customers directed to a fake bank site (also HTTPS, different domain). Credentials entered there go straight to the attacker. (2) MALWARE on customer device: keylogger records credentials before encryption. (3) CREDENTIAL STUFFING: customers reuse passwords from a breached third-party site. (4) SESSION HIJACKING: attacker steals the session cookie after login.
Investigation steps. Check server logs for unusual login locations/times. Survey affected customers — did they receive suspicious emails? Check third-party breach databases (HaveIBeenPwned) for customer email exposure. Scan for malware injection in bank's own web code.
Layered defence strategy. (1) MFA: stolen password alone is insufficient — attacker also needs the one-time code. (2) Email security: DMARC/DKIM/SPF to prevent spoofed bank emails used in phishing. (3) Certificate Transparency monitoring: detect rogue certificates for lookalike domains. (4) Security awareness: educate customers to check the URL and report suspicious emails. (5) Session security: short-lived tokens, secure/httpOnly cookie flags, re-authentication for sensitive actions.
Incident response. Reset all affected customer passwords, notify OAIC under the Notifiable Data Breaches scheme, engage ASD's ACSC for threat intelligence, and review logs to understand the full scope.

Answer: No single control is sufficient. A layered "defence-in-depth" strategy addresses the technical, human and procedural dimensions simultaneously.

Practice questions

HTTPS protects your data by:
1. Blocking all websites except approved ones.
2. Encrypting communication between browser and server.
3. Storing your passwords securely.
4. Verifying you are over 18.
(1 marks)
Explain why "human factors" are often considered the weakest link in cybersecurity.
(3 marks)
Which ASD "Essential Eight" mitigation involves ensuring users cannot install unapproved software?
1. Multi-factor authentication
2. Application control
3. Patch management
4. Regular backups
(1 marks)
A Victorian school network is targeted by a ransomware attack. Explain how the attack likely occurred and describe four specific controls that could have prevented it.
(4 marks)
Compare TCP and UDP. Give one use case where each is preferred.
(2 marks)

Deeper Understanding: How TLS Encryption Actually Works

When your browser connects to a secure website (HTTPS), it uses TLS (Transport Layer Security) to negotiate an encrypted channel. The process begins with a "handshake": your browser and the server agree on an encryption algorithm, and the server presents a digital certificate signed by a trusted Certificate Authority (CA). Your browser checks this certificate is valid and hasn't been revoked.

The clever part is key exchange. Both parties need to agree on a secret encryption key without transmitting it openly. Modern TLS uses Elliptic Curve Diffie-Hellman (ECDH) — a mathematical technique where both parties exchange public values but only they can compute the shared secret. An eavesdropper who intercepts the exchange cannot derive the key — this property is called "perfect forward secrecy."

In Australia, the Australian Signals Directorate (ASD) publishes the Information Security Manual (ISM), which specifies the encryption standards and configurations that government systems must use. Private organisations operating critical infrastructure must comply with the Security of Critical Infrastructure Act 2018 and its associated rules.

The emergence of quantum computing poses a future threat to current encryption. Quantum computers can potentially break the mathematical problems (factoring, discrete logarithm) that underpin RSA and ECDH. This is why cryptographers and government agencies worldwide are developing post-quantum cryptography standards — NIST finalised its first post-quantum algorithms in 2024, beginning a transition that will take decades but is already underway in highly sensitive systems.

Summary

Networks transmit data as packets using protocols (HTTP, TCP/IP); hardware includes routers, switches and firewalls.
Cybersecurity threats include phishing, malware, MitM, DDoS and social engineering.
Defences require multiple layers: encryption, MFA, updates, backups, user education and network segmentation.
HTTPS encrypts the channel but does not guarantee a website is legitimate.
Australia's ASD "Essential Eight" provides a framework of prioritised security mitigations.
The "human firewall" — educating users — is as important as technical controls because 80-90% of breaches involve human error.