Network Security Basics: Threats, Protocols, and Safeguards

Core Concepts: Why Security Matters in Networks

Network security is the practice of protecting data, devices, and systems from unauthorized access, misuse, or attacks. In business, a single breach can cost millions (e.g., Nepal Rastra Bank’s 2021 cyberattack, which exposed customer data) and damage reputation. This unit covers:

1. Threats and vulnerabilities (what attackers exploit).
2. Security protocols (how data stays safe in transit).
3. Defensive tools (firewalls, encryption, authentication).
4. Real-world case studies (how companies like Khalti or NTC implement security).

1. Types of Network Security Threats

Threats exploit weaknesses in networks, software, or human behavior. Classify them as:

mindmap
  root((Network Threats))
    Malware["Malware\n(Viruses, Worms, Ransomware)"]
      Virus["Attaches to clean files (e.g., 2017 WannaCry ransomware)"
            "Spreads via email/USB drives"]
      Ransomware["Encrypts data; demands payment (e.g., 2020 Nepal hospital attacks)"]
      Trojan["Disguised as legitimate software (e.g., fake 'eSewa update' apps)"]
    Unauthorized Access["Gaining control without permission"]
      Phishing["Fake emails (e.g., 'Your Khalti account is locked!')"]
      Brute Force["Guessing passwords (e.g., weak Wi-Fi passwords in cafes)"]
      Man-in-the-Middle["Intercepting data (e.g., public Wi-Fi eavesdropping)"]
    Denial-of-Service["Overloading systems to crash them"]
      DDoS["Botnets flood targets (e.g., 2021 Daraz website outages)"]
    Insider Threats["Employees/malicious admins (e.g., 2020 Ncell employee leak)"]
    Physical Threats["Theft/damage to hardware (e.g., stolen routers in offices)"]

Worked Example: Phishing Attack on eSewa

1. Attack: A user receives an email: "Your eSewa transaction failed! Click here to verify."
2. Red Flags:
   • URL: eSewa-verify[.]com (not eSewa[.]com).
   • Generic greeting: "Dear User" (legit emails use your name).
3. Outcome: Clicking installs malware stealing login credentials. Prevention: Always verify URLs and use multi-factor authentication (MFA).

2. Security Protocols: How Data Stays Safe

Protocols encrypt data or authenticate users. Key ones:

How a browser and server establish an encrypted connection (Image: Essich, CC BY 3.0, via Wikimedia Commons)

Worked Example: HTTPS vs. HTTP

• HTTP: Unencrypted (passwords/credit cards visible to attackers).
• HTTPS: Uses TLS to encrypt data.
  • Trace: When you log into Khalti, your browser checks for a valid SSL certificate (issued by GlobalSign or DigiCert). If missing, Chrome shows:

    "Your connection is not private" → *Attackers could steal your data!

3. Defensive Tools: Firewalls, Encryption, and Authentication

A. Firewalls: The Network Bouncer

Firewalls filter traffic based on rules. Types:

flowchart TD
  A["Firewall Types"] --> B["Packet-Filtering\n(Routers, basic rules)"]
  A --> C["Stateful Inspection\n(Tracks connections, e.g., NTC network)"]
  A --> D["Application-Level\n(Deep packet inspection, e.g., banks)"]
  A --> E["Next-Gen\n(Uses AI to detect threats, e.g., Daraz servers)"]

Example: Nepal Rastra Bank’s firewall rules:

• Block: Port 22 (SSH) from public IPs → Only internal admins can access.
• Allow: Port 443 (HTTPS) → Secure web traffic.

B. Encryption: Scrambling Data

• Symmetric Key: Same key encrypts/decrypts (fast, e.g., AES-256 in WhatsApp).
• Asymmetric Key: Public/private keys (secure, e.g., RSA in SSL).
• Hashing: One-way encryption (e.g., storing passwords as SHA-256 hashes).

C. Authentication: Proving You’re Who You Say

Methods ranked by security:

Worked Example: Ncell’s Biometric Security

1. Process:
   • User registers fingerprint/iris at Ncell store.
   • Device stores a template (not the actual image).
   • For transactions, the phone matches live scan to template.
2. Why It Works: Harder to replicate than passwords.

4. Real-World Case Study: The 2022 Ncell Data Leak

What Happened:

• A third-party vendor’s database was exposed online (unencrypted).
• 1.2 million customers’ data (names, phone numbers, SIM details) leaked.
• Impact: Phishing scams surged; some users received fake "Ncell upgrade" calls.

How It Could Have Been Prevented:

1. Encryption: Store data as AES-256 encrypted backups.
2. Access Control: Only allow vendors to access minimal data (e.g., no full customer lists).
3. Monitoring: Use SIEM tools (like Splunk) to detect unauthorized access.

Lesson: Even large companies fail due to human error or third-party risks.

5. Network Security in Business: Applying the Concepts

Businesses use security to:

• Protect transactions (e.g., eSewa’s PCI-DSS compliance).
• Prevent downtime (e.g., NTC’s DDoS protection).
• Meet legal requirements (e.g., Nepal’s 2018 Cyber Security Act).

Example: Daraz’s Security Measures

In the Real World

1. eSewa’s SSL/TLS:

   • When you transfer money, your browser checks for a valid SSL certificate (issued by DigiCert). If expired, the transaction fails → Prevents MITM attacks.
   • How it works: Your phone and eSewa’s server perform a TLS handshake to agree on encryption keys.

2. Khalti’s MFA:

   • After entering your password, Khalti sends an OTP via SMS. Even if hackers steal your password, they can’t bypass the OTP.
   • Real scenario: In 2021, a Khalti user reported fraud after reusing a weak password. MFA blocked the attacker.

3. NTC’s Firewall Rules:

   • NTC blocks inbound RDP (port 3389) to prevent brute-force attacks on internal servers.
   • Why it matters: In 2020, a Nepalese ISP was hacked via an unpatched RDP server.

Exam Tip: How to Score Full Marks

1. Define and Differentiate:

   • Always start with clear definitions (e.g., "SSL provides encryption; TLS is its updated version").
   • Compare protocols in tables (e.g., SSL vs. IPSec).

2. Use Real Examples:

   • Link threats to Nepali companies:
     • "A DDoS attack on Daraz would disrupt e-commerce, costing merchants sales."
   • Cite laws:
     • "Nepal’s Cyber Security Act 2018 mandates encryption for sensitive data."

3. Diagrams Are Your Friends:

   • Draw firewall rule sets or encryption workflows (e.g., how AES works).
   • Use mindmaps for threat classifications.

4. Common Pitfalls to Avoid:

   • ❌ "Firewalls prevent all viruses." → False. Firewalls block network-level threats; antivirus handles malware.
   • ❌ "VPNs are 100% secure." → False. Weak passwords can still be brute-forced.

5. Case Study Approach:

   • If asked "How would you secure eSewa?", structure your answer:
     1. Threat: Phishing → Solution: MFA + email verification.
     2. Threat: Data leaks → Solution: Encrypted databases + access logs.

Quick Revision Checklist

• Can you list 5 types of malware and give a Nepali example for each?
• Draw the TLS handshake steps (3-way process).
• Compare symmetric vs. asymmetric encryption in a table.
• Explain how Ncell’s biometric system prevents fraud.
• Name 3 security protocols used in banking and their weaknesses.