IPsec (Internet Protocol Security) is a suite of protocols used to secure communications over IP networks—like the internet or private networks. It’s especially common in VPNs (Virtual Private Networks), where it helps keep data private and tamper-proof.

🧩 What IPsec Does

• Encrypts data so unauthorized parties can’t read it
• Authenticates the source of data to ensure it’s legitimate
• Ensures integrity, meaning the data hasn’t been altered in transit
• Protects against replay attacks, where old data packets are resent maliciously

🛠️ How It Works

IPsec operates in two main modes:

• Transport Mode: Encrypts only the payload (the actual data), leaving the header intact—used for end-to-end communication between devices
• Tunnel Mode: Encrypts the entire IP packet—used for network-to-network communication, like between two VPN gateways

It uses two key protocols:

• AH (Authentication Header): Provides authentication and integrity
• ESP (Encapsulating Security Payload): Provides encryption, authentication, and integrity

🔑 Key Management

IPsec relies on IKE (Internet Key Exchange) to securely negotiate and manage cryptographic keys between devices.

🧪 Real-World Use

Imagine sending a confidential letter through the mail. Without IPsec, it’s like writing your message on a postcard—anyone can read it. With IPsec, it’s sealed in an envelope, signed, and tracked to ensure it reaches the right person without tampering.