Handshake Protocol

The Handshake Protocol is a critical component of SSL/TLS that establishes a secure communication channel between a client (such as a web browser) and a server. During the handshake, both parties agree on encryption methods, verify each other’s identities through digital certificates, and generate shared cryptographic keys for encrypting the session. This process ensures that any data exchanged afterward is both confidential and tamper-proof. Without the handshake, encrypted communication on the internet would not be possible, making it one of the most important steps in secure online interactions.

How it works

  1. Client Hello → The client sends a request to the server with supported encryption algorithms and a randomly generated value.
  2. Server Hello → The server responds with its chosen encryption method, a digital certificate, and another random value.
  3. Key Exchange → The client and server exchange information (often using RSA, Diffie-Hellman, or Elliptic Curve methods) to establish a shared session key.
  4. Authentication → The client verifies the server’s certificate against a trusted Certificate Authority (CA).
  5. Session Established → Both sides now use the shared session key to encrypt and decrypt communication.

Why it matters

The handshake protocol ensures that communication is secure from the very beginning of a connection. It prevents attackers from intercepting or altering data by confirming the server’s identity and establishing encryption before any sensitive information is shared. A secure handshake is fundamental to online banking, e-commerce, private messaging, and any service that relies on encrypted connections.

Examples

  • When visiting an HTTPS website, your browser and the web server complete a TLS handshake before loading the page.
  • VPN clients establish a secure handshake with VPN servers before tunneling encrypted traffic.
  • Mobile apps that connect to APIs perform TLS handshakes to secure data exchanges.