5.1 The Internet and its uses

The Internet and the WWW

1. Internet vs. World Wide Web (WWW)

Many people use these terms interchangeably, but in Computer Science, they are distinct entities.

The Internet

The Hardware/Infrastructure. A massive global network of networks connected via copper wires, fiber optics, and satellites.

World Wide Web

The Service/Software. A collection of information (webpages) stored on servers, accessed via the internet using the HTTP protocol.

2. Retrieving a Webpage: HTTP, HTTPS, and Security

HTTP (Hypertext Transfer Protocol) is the set of rules used to transfer files (text, images, video) on the web.

Protocol Description
HTTP Data is sent in "Plain Text." Anyone intercepting the data can read it.
HTTPS HTTP Secure. Data is encrypted using SSL or TLS.

The Role of SSL and TLS

SSL (Secure Sockets Layer) and its successor TLS (Transport Layer Security) provide a secure link between the browser and the server.

  • They use Encryption to scramble data so hackers cannot understand it.
  • They use Certificates to authenticate that the server is who it claims to be (avoiding "spoofing").

3. The Domain Name System (DNS)

Computers communicate using IP Addresses (e.g., 192.0.2.1), but humans prefer words. The DNS acts as the "Phonebook" of the internet.

The Process:
  1. You type www.google.com into your browser.
  2. The browser sends a request to a DNS Server.
  3. The DNS looks up the IP Address for that domain.
  4. The IP address is sent back to your browser, which then contacts the server directly.

4. Anatomy of a URL

A Uniform Resource Locator is the complete web address used to find a specific resource.

https:// www.example.com /folder/ index.html
  • Protocol: How the data is sent (HTTP/HTTPS).
  • Domain Name: The name of the server/website.
  • Path: The specific folder on the server.
  • Filename: The actual web page or image file.

5. Features of a Web Browser

A browser is an application software that renders HTML code into the visual webpage you see.

Address Bar (URL Entry)
Navigation (Back/Forward)
Bookmarks/Favorites
History (Past visits)
Tabs (Multi-page viewing)
Cookies Management
⚠️ Exam Summary:

The browser requests a page using a URL. The DNS finds the IP Address. The server sends HTML files via HTTPS, which uses TLS/SSL for encryption. The browser then renders the code for the user.

End of Internet & WWW Notes • Ready for Web Browser specifics or Cookies?

Blockchain and Digital Currency

1. What is Blockchain?

A Blockchain is a digital, decentralized ledger that records transactions across many computers. Once a piece of data is recorded, it cannot be changed without altering all subsequent blocks.

The "Shared Diary" Analogy

Imagine a classroom where every student has an identical diary. When the teacher gives a sticker to a student, everyone writes it down at the same time.

  • If one student tries to secretly erase a page or change a name, their diary won't match the other 29 diaries.
  • The class compares diaries regularly. If one doesn't match, it is rejected.
  • This creates Trust without needing a Principal (Central Authority) to watch over them.
Block 1
Data + Hash
➔
Block 2
Link to B1
➔
Block 3
Link to B2

2. Digital Currency (Cryptocurrency)

Digital currency is a medium of exchange that exists only in electronic form. It uses blockchain technology to track who owns what.

Examples: Bitcoin (BTC), Ethereum (ETH), Litecoin (LTC).

How it works in Finance:

  1. Transaction: Someone requests a transfer of currency.
  2. P2P Network: The request is broadcast to a global network of computers (Nodes).
  3. Validation: The nodes verify the transaction using algorithms.
  4. The Block: Once verified, the transaction is combined with others to create a new block of data for the ledger.
  5. Completion: The block is added to the existing chain, and the money is "moved."

3. Advantages & Limitations

Advantages

  • Security: Nearly impossible to hack due to decentralization.
  • Transparency: Every transaction is visible on the public ledger.
  • No Middleman: No need for banks, which reduces transaction fees.
  • Global: Can be sent anywhere in the world instantly.

Limitations

  • Volatility: Prices can crash or skyrocket in minutes.
  • Environment: "Mining" (verifying blocks) uses massive amounts of electricity.
  • Irreversible: If you lose your "Private Key" (password) or send money to the wrong address, it is gone forever.
  • Crime: Anonymity can attract illegal activities.

4. Beyond Money: Uses of Blockchain

Blockchain isn't just for currency. Because it is a "permanent record," it can be used for:

  • Smart Contracts: Agreements that execute automatically when conditions are met.
  • Voting Systems: Ensuring votes cannot be tampered with.
  • Supply Chain: Tracking exactly where a product (like organic coffee) came from.
⚠️ Exam Note: When asked why blockchain is secure, emphasize that it is "Distributed" (stored in many places) and "Immutable" (cannot be changed once written).
End of Blockchain Notes • Ready for Cybersecurity (Malware, Phishing, Cookies)?

Cyber Security Threats

1. Defining Malware

Malware (Malicious Software) is an umbrella term for any software intentionally designed to cause damage to a computer, server, client, or computer network.

The "Virus" Distinction: People often use "Virus" to mean any bad software, but technically, a Virus is a specific type of malware that must attach itself to a program and requires human action (like opening a file) to spread. Other malware, like Worms, can spread on their own.

2. Common Cyber Threats

Viruses

Code that replicates itself by attaching to other files. It can delete data or corrupt the operating system.

Example: You download a "free game" that contains a hidden script. When you run the game, the script deletes your documents.
Worms

Standalone malware that replicates itself to spread to other computers, usually across a network, without human help.

Example: A program enters a company network through one weak PC and automatically copies itself to every other PC on the server.
Trojan Horse

Software that looks legitimate but contains a hidden malicious function. It creates a "backdoor" for hackers.

Example: A "PC Speed Up" tool that actually installs software allowing a hacker to control your webcam remotely.
Spyware

Software that gathers information about a person or organization without their knowledge (includes Keyloggers).

Example: A hidden program records every key you press while logging into your bank and sends it to a server in another country.
Ransomware

Encrypts the user's files and demands a payment (usually in Bitcoin) to provide the decryption key.

Example: A hospital's patient records are locked; a message appears saying they must pay $50,000 to get the data back.
Phishing

Sending fraudulent communications (usually email) that appear to come from a reputable source to steal sensitive data.

Example: An email from "Paypal" tells you your account is locked and asks you to click a link to "verify" your password.
Pharming

Malicious code installed on a user's PC or a DNS server that misdirects users to a fraudulent website even if they type the correct URL.

Example: You type "www.bank.com", but the malware sends you to a fake version of the site that looks identical to the real one.
DoS / DDoS

Flooding a server with useless traffic to make it crash or become unavailable to legitimate users.

Example: Millions of automated "requests" hit a school's website at once, causing the server to shut down during exam results day.

3. Social Engineering

Many of these threats rely on Social Engineering. This is the art of manipulating people so they give up confidential information. It targets the human rather than the hardware.

⚠️ Exam Alert: Phishing vs. Pharming
  • Phishing: Uses an Email to lure the user.
  • Pharming: Uses Malicious Code to redirect the user (even if they type the right address).
End of Security Threats Notes • Ready for Protection Measures (Firewalls, Encryption, MFA)?

Cybersecurity Protection Measures

1. Access Control & Authentication

The first line of defense is ensuring only authorized users can access the system.

Passwords & Biometrics

Using unique strings or physical traits (Fingerprints, FaceID) to verify identity.

Requirement: Passwords should be "strong" (mixed case, symbols, numbers).

Two-Factor Authentication (2FA)

Requires two forms of identification: Something you know (password) and Something you have (a code sent to your phone).

2. Network Defenses

Firewalls

Monitors incoming and outgoing traffic. It blocks data packets that do not meet specific security criteria.

  • Prevents unauthorized access.
  • Can block specific IP addresses or ports.
Proxy Servers

Acts as an intermediary. It hides the user's real IP address from the web and can filter out malicious websites before they reach the user.

3. Data Protection: Encryption

If data is stolen or intercepted, Encryption ensures the thief cannot read it.

How it Works

Plaintext is converted into Ciphertext using an algorithm and a "Key."

PLAINTEXT + KEY ➔ CIPHERTEXT

Symmetric Encryption: Uses the same key for both encrypting and decrypting. (Risky to share the key).

Asymmetric Encryption: Uses a Public Key to encrypt and a Private Key to decrypt. (Much more secure for the Internet).

4. Software Defense

Anti-Malware Software

Scans files against a database of known "Signatures" of malware. If a match is found, the file is quarantined or deleted.

Security Updates (Patches)

Software developers release "patches" to fix security holes (vulnerabilities) discovered in their programs. Keeping software updated is vital.

5. Human Defenses

Since many attacks target humans (Social Engineering), education is the best defense:

  • Don't click: Links in suspicious emails.
  • Verify: Check the URL of a website before entering data (look for the padlock 🔒).
  • Privacy Settings: Limit what you share on social media.
⚠️ Exam Tip: If asked how to protect a network, mention Firewalls and Proxy Servers. If asked how to protect data being sent, the answer is Encryption.
End of Protection Measures Notes • Chapter 5 Complete.

Cookies

1. What are Cookies?

A Cookie is a small text file sent by a web server to a user's web browser. It is stored on the user's hard drive and contains information about the user's visit to a website.

Crucially: Cookies are not programs; they cannot carry viruses or delete files. They are just data.

2. Types of Cookies

Session Cookies

Stored in temporary memory. They are deleted as soon as the browser is closed.

Use: Keeping items in a shopping basket while you browse different pages.

Persistent Cookies

Stored on the hard drive until they reach their expiry date or are manually deleted.

Use: "Remember me" login details and user preferences (like Dark Mode).

3. Uses of Cookies

  • Personalization: Remembering your language choice or theme.
  • Authentication: Keeping you logged in as you move between pages.
  • Tracking/Analytics: Helping website owners see how many people visit and which pages are popular.
  • Targeted Advertising: Tracking your interests across different sites to show you "relevant" ads.

4. Privacy Implications

While cookies make the web easier to use, they raise significant Privacy Concerns:

  • Tracking: Third-party cookies can follow you across different websites, building a profile of your behavior without your explicit knowledge.
  • Data Sharing: Information collected by cookies can be sold to advertisers or other companies.

Side Note: The GDPR and "Cookie Banners"

The GDPR (General Data Protection Regulation) is a strict EU law that forces websites to ask for your explicit consent before using non-essential cookies.

Where did this come from? In the early 2000s, "Zombie Cookies" and invisible tracking became widespread. EU lawmakers felt that the "right to be forgotten" and the right to privacy were fundamental human rights. They wanted to stop companies from "silently" profiling citizens without their permission, leading to the "Accept All Cookies" pop-ups we see today.

⚠️ Exam Note: If asked for a benefit of cookies, mention "user convenience" (e.g., shopping baskets). If asked for a drawback, mention "invasion of privacy" or "tracking user habits."
End of Cookie Notes • Ready for Cybersecurity Protection Measures?