🔐 Encryption
Protects data from unauthorized users. Algorithms: AES-256, RSA, SHA.
VPN
✅ What is a VPN?
VPN (Virtual Private Network) is a technology that creates a secure, encrypted connection over a public network (like the Internet) to another network (such as your company's internal network or a private server).
🔧 How VPN Works (Step-by-Step)
-
📌 Step 1: VPN Client Initiates Connection
User (client) opens a VPN app and connects to a VPN server.
-
📌 Step 2: Authentication
The VPN client authenticates with the VPN server using credentials (username/password, certificates, etc.).
-
📌 Step 3: Tunnel is Created
A secure tunnel is established between the client and the server using protocols like:
- OpenVPN
- IPSec
- L2TP
- WireGuard
-
📌 Step 4: Data is Encrypted
All internet traffic from the user’s device is encrypted before leaving the device.
-
📌 Step 5: Data Travels via VPN Server
Encrypted data goes to the VPN server → decrypted → sent to the destination.
-
📌 Step 6: Response Comes Back
Data comes back to the VPN server → encrypted → sent to the client → decrypted.
📦 Use Cases of VPN
| Use Case | Description |
|---|---|
| 🔒 Secure Public Wi-Fi | Protects data from hackers on public Wi-Fi. |
| 🌍 Bypass Geo-Restrictions | Access blocked sites (e.g., Netflix USA from India). |
| 👨💼 Remote Work | Secure access to company resources from home. |
| 🕵️♂️ Online Privacy | Hides your IP address and encrypts traffic. |
| 🚫 Bypass Censorship | Access restricted sites in censored countries. |
| 🏢 Site-to-Site VPN | Connects two office networks securely. |
| 🧪 Testing from Different Locations | Test websites from different regions. |
🧠 Important Concepts to Know for Interviews
🌐 Tunneling Protocols
Encapsulate and encrypt data. Examples:
- PPTP – Fast but outdated
- L2TP/IPSec – Secure, widely supported
- OpenVPN – Secure, open-source
- WireGuard – New, fast, lightweight
📡 IP Masking
Replaces your real IP with server’s IP.
🛡️ Kill Switch
Cuts off internet if VPN drops.
🔄 Split Tunneling
Some traffic uses VPN; some goes direct.
🏛️ Types of VPN
- Remote Access VPN
- Site-to-Site VPN
- Client-based VPN
- Browser-based VPN
🔍 VPN vs Proxy
| Feature | VPN | Proxy |
|---|---|---|
| Encryption | Yes | No |
| Anonymity | High | Low |
| Speed | Slower | Faster |
| Application | Entire device | Specific apps |
⚠️ VPN Limitations
- Slower speed (due to encryption)
- Server can still track
- Not a substitute for antivirus
- Some sites block VPNs
✅ Interview-Ready Points
- Provides confidentiality, integrity, secure access.
- Encryption & tunneling are key.
- Used for secure comms over public networks.
- Helps bypass geo-blocks & censorship.
- Features: split tunneling, kill switch.
- Used in personal & corporate scenarios.