TECHNOLOGY 

Published on
KembaraXtra- Computer Science - Bitcoin
I. Cryptocurrency Fundamentals
A. Definition
  • A digital asset used for financial transactions, serving as an alternative to traditional currencies.
B. Uses
  • Transactional: Spending currency on goods/services.
  • Investment: Similar to gold; value is stored/speculated on.
C. Key Characteristic: Decentralization
  • No single controlling organization.
II. Bitcoin Basics
A. Origin
  • The first decentralized cryptocurrency, introduced in 2009.
B. Dominance
  • Most well-known cryptocurrency, with many alternatives ("altcoins") but none as dominant.
C. Unit of Currency
  • Bitcoin (BTC).
III. Blockchain Technology
A. Core Concept
  • Information grouped into chronological "blocks" linked together.
B. Bitcoin's Use of Blockchain
  • Blocks contain transaction records (movement of bitcoins).
C. Network Operation
  • Operates over a network (e.g., the internet).
  • Multiple computers ("nodes") process transactions and update the blockchain.
  • No single master copy of the blockchain.
D. Security
  • Encryption/Decryption: Ensures transaction integrity and prevents tampering.
  • Immutability: Data cannot be changed once written to the blockchain.
E. Bitcoin's Blockchain as a Public Ledger
  • Decentralized, immutable record of all Bitcoin network transactions.
IV. Bitcoin Wallets
A. Storage
  • Bitcoins are associated with key pairs held in a Bitcoin wallet.
  • The wallet holds cryptographic key pairs (private and public keys).
B. Key Pairs
  • Private Key: Randomly generated 256-bit number; must be kept secret. Allows spending of associated bitcoins.
  • Public Key: Derived from the private key; used to receive bitcoins.
C. Bitcoin Address
  • Text string generated from the public key; used to represent the public key when receiving bitcoins.
  • Example: 13pB1brJqea4DYXkUKv5n44HCgBkJHa2v1
D. Sending and Receiving Bitcoins
  • Sender needs the recipient's Bitcoin address (derived from their public key).
  • Sender uses their private key to authorize the transaction.
  • Recipient's private key is never shared.
V. Bitcoin Transactions
A. Definition
  • A transfer of bitcoins.
B. Process
  1. Wallet software constructs a transaction.
  2. Transaction details (sender, receiver, amount) are specified.
  3. Digitally signed with the sender's private key.
  4. Broadcast to the Bitcoin network.
  5. Network computers verify the transaction.
  6. Transaction added to a new block on the blockchain.
C. Structure
  • Inputs: Source of the bitcoins being transferred. Refers to a previous transaction's output, not directly to a Bitcoin address.
  • Outputs: The address where the bitcoin is sent.
D. Bitcoin Balance
  • Not explicitly stored in the wallet or directly in the blockchain.
  • Calculated from the history of transactions associated with an address.
VI. Bitcoin Mining
A. Definition
  • The process of maintaining the Bitcoin blockchain.
B. Miners
  • Computers around the world that add blocks of transactions to the blockchain.
C. Mining Process
  1. Verify Transactions: Ensure each transaction in the block is valid.
  2. Solve a Complex Problem: Miners must solve a computationally difficult problem (proof of work).
D. Proof of Work
  • Deters tampering with the blockchain.
  • Altering a block requires re-solving the problem for that block and all subsequent blocks.
E. Mining Rewards
  • The first miner to solve the problem is awarded a sum of bitcoins.
  • This is how new bitcoins are created.
  • Miners also claim transaction fees from transactions included in the block.
F. Bitcoin Limit
  • Designed to allow only 21 million coins to be mined in total.
  • After that, miners will rely solely on transaction fees.
VII. Bitcoin Origins
A. Genesis Block
  • The first block in the Bitcoin blockchain, mined in 2009.
B. Satoshi Nakamoto
  • Inventor of Bitcoin (presumed pseudonym).
C. Mining Profitability
  • Mining costs (hardware, electricity) must be less than the value of bitcoins awarded.
  • Specialized hardware is used for faster mining.
  • Mining is not a guaranteed profit due to costs and price volatility.
VIII. Anonymity and Blockchain Applications
A. Bitcoin Anonymity
  • The blockchain is public (all transactions are visible).
  • However, personal identities are not directly linked to addresses.
  • Attracts those seeking anonymity.
B. Blockchain Technology
  • Can be used beyond cryptocurrencies.
  • Suitable for any system needing a tamper-resistant record history.
Picture
Published on
KembaraXtra-Computer Science - Deep Web and Dark Web
I. Overview
  • The internet can be divided into three layers:
    • Surface Web
    • Deep Web
    • Dark Web
  • The terms "Deep Web" and "Dark Web" are often confused but have distinct meanings.
II. Surface Web
  • Definition: Content freely available and accessible to anyone.
  • Examples: Public blogs, news sites, public social media posts (e.g., public Twitter posts).
  • Indexing: Indexed by search engines (Google, Bing, etc.).
  • Accessibility: Can be found using standard search engines.
III. Deep Web
  • Definition: Web content that cannot be accessed without logging in or specific credentials.
  • Accessibility: Requires a password or login to access.
  • Examples:
    • Checking your bank balance online.
    • Reading your email through a web service (Gmail, Yahoo, etc.).
    • Logging into social media accounts (Facebook, Instagram, etc.).
    • Viewing personal shopping history on e-commerce sites (Amazon, etc.).
  • Indexing: Not indexed by search engines; therefore, not publicly available.
  • Reason for Non-Indexing: To protect sensitive, private user data.
IV. Dark Web
  • Definition: Web content that requires specialized software to access.
  • Accessibility: Cannot be accessed with a standard web browser.
  • Key Technology: Tor (The Onion Router) is the most prevalent technology.
  • Tor Functionality:
    • Enables anonymous access to the web.
    • Uses a system of encryption and relays.
    • Hides the user's IP address, preventing ISPs from monitoring browsing activity.
    • Prevents visited sites from knowing the visitor's IP address.
  • Onion Services: Websites accessible only through Tor, and are part of the Dark Web. They also hide their IP addresses.
  • Anonymity: Both users and websites can remain anonymous.
  • Use Cases:
    • Criminal Activity: Anonymity can be exploited for illegal purposes.
    • Legitimate Purposes:
      • Whistleblowing
      • Political discussion
  • Caution: Exercise caution when accessing content on the dark web.
Picture
Published on
KembaraXtra-Computer Science - Cloud Computing
I. Introduction to Cloud Computing
  • Definition: Delivery of computing services over the internet.
  • Shift from centralized to local to remote computing.
  • Cloud computing allows on-demand purchasing of computing services.
II. History of Remote Computing
  • Early Days: Centralized computing with servers accessed via terminals.
  • Shift to Local: Desktop computers handled processing locally.
  • Return to Remote: Web-based applications accessed via local smart devices.
  • Modern applications use a mix of local and remote processing.
III. The Need for Cloud Computing
  • Maintaining servers is complex and costly (hardware, software, security, capacity planning).
  • Organizations want to focus on their core purpose, not server maintenance.
  • Cloud providers handle the underlying hardware and infrastructure.
IV. Categories of Cloud Computing
  • Defined by the division of responsibility between cloud provider and consumer.
  • Four main categories: IaaS, PaaS, FaaS, SaaS
A. Infrastructure as a Service (IaaS)
  • Provider: Manages hardware and virtualization.
  • Consumer: Manages OS, runtime environment, application code, and data.
  • Example: Virtual computer (VM or container) accessed over the internet.
  • Responsibility: Consumer maintains all software on the virtual computer.
  • Examples: Amazon EC2, Microsoft Azure Virtual Machines, Google Compute Engine
B. Platform as a Service (PaaS)
  • Provider: Manages hardware, virtualization, OS, and runtime environment.
  • Consumer: Develops and manages the application code.
  • Benefit: Consumer doesn't maintain the underlying OS or runtime environment.
  • Responsibility: Consumer manages application and provisions resources (storage, VMs).
  • Examples: AWS Elastic Beanstalk, Microsoft Azure App Service, Google App Engine
C. Function as a Service (FaaS)
  • Provider: Manages all infrastructure and on-demand execution of code.
  • Consumer: Only deploys code (functions) that run in response to events.
  • Model: Event-driven.
  • Serverless Computing: Consumer doesn't manage servers.
  • Responsibility: Consumer writes code that runs in response to events.
  • Examples: AWS Lambda, Microsoft Azure Functions, Google Cloud Functions
D. Software as a Service (SaaS)
  • Provider: Fully manages the application in the cloud.
  • Consumer: Uses the complete application.
  • Contrast: Differs from installing and maintaining software locally.
  • Responsibility: Consumer manages the data they store in the application.
  • Examples: Microsoft 365, Google G Suite, Dropbox
V. Major Cloud Providers
  • Amazon Web Services (AWS)
  • Microsoft Azure
  • Google Cloud Platform (GCP)
  • IBM Cloud
  • Oracle Cloud
  • Alibaba Cloud
VI. Key Concepts
  • Runtime Environment: Environment in which an application executes (libraries, interpreters, etc.).
  • Virtualization: Creating a virtual (rather than actual) version of something, such as a computer hardware platform, operating system, storage device, or network resources
  • Serverless Computing: Cloud computing model where the provider manages servers, and the consumer doesn't need to manage them.
  • Event-Driven Model: A programming paradigm in which the flow of the program is determined by events (e.g., user actions, sensor outputs, messages from other programs/threads).



Picture
Published on
KembaraXtra- Computer Science -Virtualization and Emulation
I. Introduction
  • Virtualization: Creating a virtual representation of a computer using software.
  • Emulation: Enabling applications designed for one type of device to run on a different type of device.
II. Virtualization
  • Virtual Machine (VM): A virtual computer that runs an operating system and applications, similar to a physical computer.
    • Applications running on a VM perceive the virtualized hardware as a physical computer.
  • Benefits of Virtualization:
    • Run multiple operating systems on a single physical machine.
    • Datacenters can host multiple virtual servers on one physical server.
    • Easy to back up, restore, and deploy VMs.
  • Hypervisors: Software platforms that run virtual machines.
    • Type 1 Hypervisor: Interacts directly with the underlying hardware, sitting below the kernel.
      • Examples: Microsoft's Hyper-V, VMware ESX.
    • Type 2 Hypervisor: Runs as an application on an operating system.
      • Examples: VMware Player, VirtualBox.
  • Containers: Provide an isolated user mode environment for running applications.
    • Share the kernel with the host OS and other containers.
    • Processes in a container can only access a subset of the host's resources (e.g., isolated filesystem).
    • Provide isolation similar to VMs but without the overhead of a separate kernel.
    • Typically limited to running the same OS as the host.
    • Examples: OpenVZ (virtualizes the entire user mode), Docker (runs individual applications).
III. Emulation
  • Definition: Using software to make one type of device behave like another.
  • Key Difference from Virtualization:
    • Virtualization offers a slice of the underlying hardware.
    • Emulation presents virtual hardware that is unlike the physical hardware.
  • Example: Running software compiled for a Sega Genesis (Motorola 68000 processor) on an x86 machine.
  • Process: The emulator translates CPU instructions from the original system to instructions that the host system can understand.
  • Overhead: Emulation introduces significant overhead because each instruction must be translated.
  • Applications of Emulation:
    • Preserving software designed for obsolete platforms.
    • Enabling old software to run on modern platforms without modification (when source code is lost or modernization is too difficult).
IV. Process Virtual Machines
  • Definition: Run an application within an execution environment that abstracts away details of the underlying OS.
  • Similarity to Emulators: Provides a platform decoupled from the hardware and OS.
  • Difference from Emulators: Does not simulate real hardware.
  • Purpose: Designed for running platform-independent software.
  • Examples: Java and .NET use process virtual machines that run bytecode.
V. Key Differences Summarized
Feature
Virtualization
Emulation

Picture
Feature Virtualization Emulation Hardware Virtualized hardware is similar to actual hardware Virtualized hardware is unlike actual hardware Purpose Run multiple OSs, isolate environments Run software for different platforms Performance Generally lower overhead than emulation Higher overhead due to instruction translation OS Requirement Often requires same or similar OS Can run software designed for different OSs
Published on
KembaraXtra- Computer Science - Apps
1. App Definition & Characteristics
  • Traditional Definition: Software programs used directly by users (interchangeable with "application").
  • Modern Meaning: Gained prominence with Apple's App Store (2008).
  • Common Characteristics:
    • Designed for end users.
    • Often target mobile devices (smartphones, tablets).
    • Distributed via internet-based digital storefronts (App Store, Google Play Store, Microsoft Store).
    • Limited system access; declare required capabilities.
    • Primarily use touchscreens for user input.
  • Native App: Software installed on a device that directly utilizes the operating system's API.
  • Web App: Designed with web technologies (HTML, CSS, JavaScript) and not tied to a specific OS.
2. Native Apps
  • Definition: Built for a specific operating system (iOS, Android).
  • Benefits of App Stores:
    • New platforms for developers.
    • New methods of distribution.
    • New ways to monetize software.
  • Development Challenges:
    • iOS and Android differ in programming languages and APIs.
    • Requires separate codebases or cross-platform frameworks (Xamarin, React Native, Flutter, Unity) for multi-platform support.
    • Many apps rely on web services.
  • Cross-Platform Frameworks: Abstract underlying OS API details, enabling code to run on multiple platforms.
  • Historical Context:
    • Steve Jobs initially envisioned web apps as the primary means for third-party development on the iPhone.
    • Apple later reversed course, allowing native app development and opening the App Store.
  • Benefits of Native Apps & App Stores:
    • Revenue source for platform holders (Apple, Google, Microsoft).
    • Exclusive content.
    • Curated list of apps with ratings.
    • Consumer trust (quality guidelines).
    • Centralized payment service.
    • Automatic updates.
  • Drawbacks:
    • Complex environment for developers (multiple stores, platforms, technologies).
    • Each marketplace has specific requirements and takes a percentage of revenue.
3. Web Apps
  • Definition: Websites that function like apps, built using web technologies (HTML, CSS, JavaScript).
  • Advantages:
    • Run on any device with a modern web browser.
    • Code only needs to be written once.
  • Disadvantages:
    • Don't have full access to device capabilities.
    • Tend to be slower than native apps.
    • Require an internet connection.
    • Generally not listed in app stores.
  • Responsive Web Design: Ensures web content renders well on various screen sizes, allowing for a single website across devices.
  • Web Development Frameworks: Angular, React, Vue.js simplify web app development and maintenance.
4. Progressive Web Apps (PWAs)
  • Definition: Websites with extra features that bridge the gap between native apps and web apps.
  • Requirements:
    • Served over HTTPS.
    • Render appropriately on mobile devices.
    • Load offline once downloaded.
    • Provide a manifest describing the app.
    • Transition quickly between pages.
  • User Experience: Feel responsive and natural, like a native app.
  • Benefits:
    • Use web technologies for apps without building multiple platform-specific apps.
    • Users can add a PWA icon to their home screen or desktop, launching it like a native app in its own window.
  • Drawbacks:
    • Don't appear in app stores (except Microsoft Store).
    • Users aren't used to installing apps from websites.
    • May not look exactly like native apps (look similar across platforms).
    • May not have the same performance or full access to platform capabilities as native apps.​
Picture
Published on

KembaraXtra – Computer Science – Web Servers

I. Client-Side vs. Server-Side Technologies

  • Client-Side: Primarily deals with what the user sees and interacts with in the web browser. Uses HTML, CSS, and JavaScript.
  • Server-Side: Deals with the logic and data processing behind the website. Any programming language or technology can be used, as long as it communicates over HTTP and returns data in a format the client understands.

II. Static vs. Dynamic Websites

Feature Static Websites Dynamic Websites
Content HTML, CSS, and JavaScript built ahead of time. HTML generated when a request comes in.
Processing Server returns pre-built files without modification. Server processes the request, often querying a database, generating HTML, and then responding.
Complexity Simpler setup. More complex setup, slower response times, potentially heavy server load, increased security risks.
Response Time Typically faster. Typically slower due to processing.
Server Load Lighter load. Heavier load.
Security Generally more secure. Potentially less secure due to increased complexity.
Example Website developed using only HTML, CSS and JavaScript files and hosted on a web server (Projects #37 through #40). A blog where posts are stored in a database and rendered into HTML when requested.

Important Note: The terms "static" and "dynamic" refer to how the content is generated on the server, not whether the website is interactive or has updated content. User experience (interactivity, content updates) is often handled with JavaScript on the client-side, regardless of whether the site is static or dynamic from the server's perspective.

III. How Static Websites Handle Requests

  1. Browser requests a specific URL.
  2. Web server receives the request.
  3. Web server finds the corresponding static file (e.g., /images/cat.jpg) in its directory.
  4. Web server returns the content of that file to the browser.
  5. The server does not modify the content.

IV. How Dynamic Websites Handle Requests

  1. Browser requests a specific URL.
  2. Web server receives the request and determines that it needs to generate HTML.
  3. The server executes code.
  4. The code queries a database and retrieves the relevant data.
  5. The server formats the data as HTML.
  6. The server responds to the client with the generated HTML.

V. The Trend Toward Static Sites

  • In recent years, there has been a shift back towards static sites where possible.
  • Static sites offer simplicity, speed, and security benefits.

VI. Hosting Static Sites

  • You need a web server software that can serve static files.
  • The software is configured to point to a directory containing the website files.
  • When a request comes in, the server returns the contents of the matching file.

VII. Building Dynamic Websites/Web Services

  • You can use existing software or write custom code to generate dynamic pages.
  • Server-side development offers a wide range of technology choices (programming languages, operating systems, databases, etc.).
  • The client doesn't care what technologies are used on the server-side; it only needs a response in a format it can handle.

VIII. Server-Side Technology Choices

  • Programming Languages: Python, C#, JavaScript (Node.js), Java, Ruby, PHP, etc.
  • Databases: Any type of database can be used.
Picture
Published on

KembaraXtra – Computer Science – Web Languages

I. Core Web Languages

A. HTML (HyperText Markup Language)

  • Purpose: Defines the structure of a web page. It determines what is on the page.
  • Key Concepts:
    • Tags: Enclosed in < and > (e.g., <p>, <h1>).
    • Elements: Consist of a start tag, content, and an end tag (e.g., <p>This is a cat.</p>). Some elements don't require end tags (e.g., <img>).
    • Structure: HTML documents have a tree-like structure with parent and child elements.
    • <!DOCTYPE html>: Declares the document as HTML.
    • <html>: The root element, containing everything else.
    • <head>: Contains document metadata (e.g., title, character set).
    • <body>: Contains the content of the web page.
    • <h1> to <h6>: Heading tags, with <h1> being the highest level.
    • <p>: Paragraph tag.
    • <img>: Image tag; src specifies image URL, alt gives alternative text.
    • Whitespace: Browsers ignore extra whitespace. Use indentation for readability.
    • HTML Living Standard: Maintained by WHATWG.
  • Example:
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>A Cat</title>
  </head>
  <body>
    <h1>Thoughts on a Cat</h1>
    <p>This is a cat.</p>
    <img src="cat.jpg" alt="cat photo">
  </body>
</html>

B. CSS (Cascading Style Sheets)

  • Purpose: Defines the appearance/style of a web page.
  • Key Concepts:
    • Rules: Define styles for specific elements.
    • Selectors: Indicate which elements are affected.
    • Cascading: Multiple rules can apply to the same element.
    • Font-family: Defines fallback fonts.
  • Methods of Application:
    • Inline: Within a <style> element – not recommended.
    • External: In a separate .css file and linked using <link> in <head>.
  • Example:
p {
  font-family: Arial, Helvetica, sans-serif;
  font-size: 11pt;
  margin-left: 10px;
  color: DimGray;
}
h1 {
  font-family: 'Courier New', Courier, monospace;
  font-size: 18pt;
  font-weight: bold;
}

C. JavaScript

  • Purpose: Defines behavior/functionality of a web page.
  • Key Concepts:
    • Interpreted Language: Executed at runtime by browser.
    • Minification: Reduces file size by removing whitespace/comments.
    • DOM: JavaScript can access and modify the page structure.
    • Event Handlers: Respond to user actions.
    • Integration: Embedded in HTML or linked via <script src="cat.js"></script>.
  • Example:
document.getElementById('cat-photo').onclick = function() {
  document.getElementById('cat-para').innerHTML += ' Meow!';
};
  • Explanation:
    • Selects element by ID.
    • Assigns a function on click.
    • Appends "Meow!" to the paragraph.
  • ECMAScript: The standardized specification for JavaScript.

    • II. Data Structuring Languages

    A. XML (Extensible Markup Language)

    • Purpose: Text-based language for data exchange.
    • Key Concepts:
      • Custom tags defined by the user.
      • Requires producer-consumer agreement.
    • Example:
    <band name="The Highbury Musical Club">
  <bandMembers>
    <member name="Jane Fairfax" instrument="Piano" />
    <member name="Emma Woodhouse" instrument="Guitar" />
  </bandMembers>
</band>

    B. JSON (JavaScript Object Notation)

    • Purpose: Lightweight data format.
    • Key Concepts:
      • JavaScript-like syntax with {} and [].
      • Compact and readable.
    • Example:
    {
  "name": "The Highbury Musical Club",
  "bandMembers": [
    {
      "name": "Jane Fairfax",
      "instrument": "Piano"
    },
    {
      "name": "Emma Woodhouse",
      "instrument": "Guitar"
    }
  ]
}
  • Usage: Used for API communication between clients and servers.

    • KembaraXtra – Computer Science – Web Browsers

    I. Introduction

    • Definition: Software applications for accessing web pages.
    • Key Functions: Requesting, receiving, and displaying web content.

    II. History of Web Browsers

    • WorldWideWeb: First browser, by Tim Berners-Lee (1990).
    • Mosaic: Brought the web to the masses.
    • Netscape Navigator: Popular in early web history.
    • Internet Explorer: Dominated the late 1990s and 2000s.
    • Modern Browsers: Chrome, Safari, Firefox.

    III. Rendering a Web Page: The Process

    1. Request: Browser sends URL request.
    2. HTML Response: Server returns HTML content.
    3. DOM Creation: Browser parses HTML into a DOM tree.
    4. Resource Requests: Additional resources (images, JS, CSS) are loaded.
    5. Rendering:
      • Displays HTML.
      • Applies CSS.
      • Executes JavaScript.
      • Updates dynamically via JS if needed.

    IV. Web Browser Architecture

    • Rendering Engine: Handles HTML/CSS layout.
    • JavaScript Engine: Runs JS code.
    • User Interface: Provides controls like the address bar.

    V. Rendering Engine Landscape

    • Key Point: Engines affect how pages look.
    • WebKit: Safari and iOS apps.
    • Blink: Chrome, Edge, Opera (Chromium-based).
    • Gecko: Firefox (with SpiderMonkey JS engine).

    VI. Understanding the User Agent String

    • Definition: The technical term for a browser is a "user agent."
    • User-Agent Header: Identifies browser during requests.
    • Example: Mozilla/5.0 (Windows NT 10.0; Win64; x64)...
    • Components Explained:
      • Mozilla/5.0: Compatibility prefix.
      • (Windows NT 10.0; Win64; x64): Platform.
      • AppleWebKit/537.36: Rendering engine.
      • (KHTML, like Gecko): History artifact.
      • Chrome/71.0.3578.98: Browser version.
      • Safari/537.36: Ensures Safari compatibility.
    • Reason for Complexity: Historical compatibility tricks.
    Picture
    Published on
    KembaraXtra -Computer Science -World Wide Web
    Core Attributes
    Distributed
    • Definition: No central authority controls web content.
    • Implications:
      • Anyone can host a web server and publish content.
      • Organizations/countries can block access.
      • Governments can shut down illegal content.
    • Key Point: The web is open and not centrally controlled.
    Addressable
    • Definition: Every web resource has a unique address (URL).
    • URL Components:
      • Scheme: Protocol (e.g., HTTP, HTTPS).
      • Authority:
        • Hostname (e.g., travel.example.com).
        • Optional: Username, Port Number.
      • Path: Location of resource on server (like a file system path).
      • Query: Modifies the resource returned (format varies by site).
    • Relative URLs:
      • Omit scheme, hostname, or full path.
      • Interpreted relative to the current context.
    • Practical URL Reading Example:
    http://travel.example.com/destinations/carolinas?location=beach
    • Uses HTTP protocol.
    • Server: travel.example.com.
    • Path: /destinations/carolinas.
    • Query: location=beach (shows beach locations).
    Linked
    • Definition: Web resources reference each other via hyperlinks.
    • Hyperlinks: One-way references, no permission needed.
    • Hypertext: Documents connected by hyperlinks.
    Protocols of the Web
    HTTP (HyperText Transfer Protocol)
    • Purpose: Transferring web resources (reading, creating, updating, deleting).
    • Foundation: Based on TCP/IP for reliable data transfer and addressing.
    • Model: Request and response.
      • Client sends an HTTP request.
      • Server replies with an HTTP response.
    HTTP Methods (Verbs)
    • GET: Retrieve a resource (no modification).
    • PUT: Create/modify a resource at a specific URL.
    • POST: Create a new resource as a child of an existing URL.
    • DELETE: Remove a resource.
    • Usage:
      • GET is most common (used for browsing and loading resources).
      • Servers often restrict PUT, POST, DELETE.
    HTTP Status Codes
    • Format: 3-digit number.
    • Classes:
      • 100s: Informational.
      • 200s: Success.
      • 300s: Redirection.
      • 400s: Client error.
      • 500s: Server error.
    • Examples:
      • 200 OK: Success.
      • 301 Moved Permanently: Redirect to a new URL.
      • 401 Unauthorized: Authentication required.
      • 403 Forbidden: Access denied.
      • 404 Not Found: Resource not found.
      • 500 Internal Server Error: Server-side error.
    HTTP Message Format
    • Request:
      • First line: Method URL HTTP/Version (e.g., GET /documents/hello.txt HTTP/1.1).
      • Headers: Additional information.
      • Optional message body.
    • Response:
      • First line: HTTP/Version Status Code Response Phrase (e.g., HTTP/1.1 200 OK).
      • Headers.
      • Optional message body.
    HTTPS (HyperText Transfer Protocol Secure)
    • Purpose: Encrypt data transmitted over the internet.
    • Encryption: Encoding data to be unreadable without decryption.
    • Cryptographic Key: Secret sequence of bytes used for encryption/decryption.
    • Encryption Types:
      • Symmetric: Single shared key for both encryption and decryption.
      • Asymmetric:
        • Public key: Encrypts data.
        • Private key: Decrypts data (kept secret).
    • Security:
      • Prevents interception and modification of data.
      • Encrypts the entire HTTP request (URL, headers, body).
    • TLS (Transport Layer Security): Protocol used to encrypt HTTP requests (formerly SSL).
    • HTTPS Handshake:
    i.Client hello: Client sends the server the encryption methods it supports.
    ii.Server hello: Server selects the encryption methods. The server provides its public key.
    iii.The client encrypts a string of bytes with the server's public key, and sends it to the server.
    iv.Server decrypts using its private key. Both compute a shared secret key for symmetric encryption.
    v.All further data is encrypted using the shared secret key.
    The Searchable Web
    • Entry Point: Often accessed through search engines.
    • Search Engines: Non-standard, proprietary systems (e.g. Google). """



    Picture
    Published on
    KembaraXtra-Computer Science-Foundational Internet Capabilities
    1. Dynamic Host Configuration Protocol (DHCP)
    • Purpose: Automatically assigns IP addresses and related network information to devices when they connect to a network.
    • Why it's important: Simplifies network configuration for end-users by eliminating the need for manual IP address assignment.
    • How it works:
      1. Discovery: A device broadcasts a message to discover available DHCP servers.
      2. Offer: The DHCP server offers an IP address from its available pool.
      3. Request: The device requests the offered IP address.
      4. Acknowledgment: The DHCP server acknowledges the request, assigning the IP address to the device.
    • Lease: IP addresses are leased to devices for a limited time. The device must renew the lease to continue using the IP address.
    • DHCP Server: A device on the network configured to provide DHCP services, including managing a pool of available IP addresses.
    2. Private IP Addresses and Network Address Translation (NAT)
    • Problem: Limited number of public IP addresses available, but many networks have multiple devices.
    • Solution: Using private IP addresses for internal network communication and NAT to share a single public IP address.
    • Private IP Addresses:
      • IP address ranges reserved for internal networks (e.g., homes, offices).
      • Ranges: 10.x.x.x, 172.16.x.x to 172.31.x.x, 192.168.x.x.
      • Non-routable on the public internet.
      • Can be used simultaneously on multiple private networks without conflict.
    • Network Address Translation (NAT):
      • Allows devices on a private network to share a single public IP address.
      • The NAT router modifies the source IP address of outgoing packets to its public IP address.
      • When responses return, the router translates the destination IP address back to the correct private IP address.
      • Security benefit: Hides devices on the private network from direct exposure to the public internet.
    • Proxy Server:
      • An alternative to NAT, typically used in corporate networks.
      • Operates at the application layer.
      • Provides additional features: User authentication, traffic logging, and content filtering.
    3. The Domain Name System (DNS)
    • Purpose: Translates human-friendly domain names (e.g., www.example.com) into IP addresses.
    • Why it's important: Makes the internet easier to use by allowing users to remember names instead of IP addresses.
    • Fully Qualified Domain Name (FQDN): The complete DNS name of a computer (e.g., travel.example.com).
      • Consists of a hostname (travel) and a domain suffix (example.com).
    • Domain: A grouping of network resources managed by an organization (e.g., example.com).
    • Resolving a Hostname: The process of querying a DNS server to find the IP address associated with a hostname.
    • Mapping:
      • One-to-many: A single name can map to multiple IP addresses (used for load balancing and geographic distribution).
      • Many-to-one: Multiple names can map to the same IP address (used for web hosting).
    • DNS Records: Entries in the DNS database.
      • A Record: Maps a hostname to an IP address.
      • CNAME Record: Maps one hostname to another hostname (alias).
      • MX Record: Used for email services.
    • DNS Hierarchy:
      • A distributed system with shared responsibility for managing DNS records.
      • Root Domain: Top of the hierarchy, contains records for top-level domains (TLDs).
      • Top-Level Domains (TLDs): (e.g., .com, .org, .edu).
      • Second-Level Domains: Registered under TLDs (e.g., example.com).
    • DNS Resolution Process:
    i.A client sends a DNS query to its configured DNS server.
    ii.If the server has the record in its cache, it returns the IP address.
    iii.If not, the server queries other DNS servers, starting at the root, to find the record.
    iv.The server caches the record for future queries.
    4. Networking in Context of Computing
    • The internet is a network of hardware and software enabling communication between devices.
    • Data transmission over the internet is based on binary data (0s and 1s).
    • Network interfaces (e.g., Wi-Fi, Ethernet) are I/O devices.
    • Operating systems use device drivers and software libraries to facilitate network communication for applications.
    • Networking devices (routers, switches) are specialized computers.
    • Networking extends computing beyond single devices.



    Picture
    Published on
    KembaraXtra-Computer Science - A Trip Through the Internet
    Overview
    This guide summarizes the journey of data across the internet using the TCP/IP model, illustrating how different devices interact at each layer.
    Scenario
    • A client device (connected to Wi-Fi) wants to access a web page hosted on a server (connected via wired connection).
    • The client knows the server's IP address.
    Step-by-Step Data Transmission
    1. Application Layer (Client):
      • The web browser creates an HTTP request.
      • The browser hands off the HTTP request to the OS's TCP/IP stack.
    2. Transport Layer (Client):
      • The TCP layer encapsulates the HTTP payload into a TCP segment.
      • It sets the destination port to 80 (standard for HTTP) in the segment header.
      • If the data is too large, TCP divides it into multiple segments.
    3. Internet Layer (Client):
      • The IP layer wraps the TCP segment in an IP packet.
      • The packet header includes the destination IP address of the server.
      • If necessary, IP divides the packet into smaller fragments.
    4. Link Layer (Client):
      • The IP packet is encapsulated in a frame.
      • The frame header includes the MAC address of the local router.
      • The client's Wi-Fi hardware transmits the frame wirelessly.
    5. Wireless Access Point:
      • Receives the frame.
      • Sends the frame to the router (operates at the link layer).
    6. Router(s):
      • Examines the IP packet to determine the destination IP address.
      • Encapsulates the packet in a new frame with the MAC address of the next router.
      • Sends the new frame on its way.
      • This routing process continues through multiple routers.
    7. Final Router (Server's Subnet):
      • Encapsulates the packet in a frame suitable for the server's local network.
      • The frame header includes the MAC address of the server.
    8. Switch (Server's Subnet):
      • Looks at the MAC address in the frame.
      • Forwards the frame out the appropriate physical port to the server.
      • Doesn't need to look at higher layers.
    9. Server:
      • Receives the frame.
      • The network interface driver passes the TCP/IP packet up to the TCP/IP stack.
      • The TCP/IP stack hands off the HTTP data to the process listening on TCP port 80.
      • The web server software (listening on port 80) handles the request.
    10. Reverse Process (Server to Client):
      • The server replies to the client, and the entire process happens again in reverse order.
    Key Concepts
    • Encapsulation: Each layer adds its own header to the data from the layer above.
    • Decapsulation: Each layer removes its header to reveal the data for that layer.
    • Routers: Operate at the internet layer (primarily) to forward packets between networks based on IP addresses.
    • Switches: Operate at the link layer to forward frames within a local network based on MAC addresses.
    • Ports: Used by the transport layer (TCP/UDP) to identify specific applications or services on a host.
    Important Notes
    • Devices interact at different layers of the TCP/IP stack.
    • The routing process involves multiple routers, each forwarding the packet closer to its destination.
    • The switch forwards data based on MAC addresses within the local network.



    Picture

    Author

    Write something about yourself. No need to be fancy, just an overview.