How SSL/TLS handshake Works

In today’s digital landscape, data security is crucial, especially as we share sensitive information online. SSL (Secure Sockets Layer) certificates are foundational to that security, ensuring that data sent between a client (like a web browser) and a server (like a website) is encrypted and protected.

1. What is an SSL Certificate?

An SSL certificate is a digital certificate that authenticates a website’s identity and enables an encrypted connection. Think of it as a digital passport that establishes the credentials of a website. When a browser reaches a site with SSL, it can trust that the connection is secure and private.

Key Points of an SSL Certificate

• Encryption: SSL encrypts data, converting it into code to prevent unauthorized access.
• Authentication: It verifies that the server (website) is who it claims to be.
• Data Integrity: It ensures that data is not altered during transfer between client and server.

2. How SSL Works: The Process Between Client and Server

The SSL process includes several steps, often referred to as the SSL/TLS handshake. Here’s how it unfolds:

Step-by-Step Breakdown

1. Client Hello:
   • The process starts when a client (e.g., your web browser) connects to an SSL-secured website.
   • The client sends a “Client Hello” message, which includes information like the SSL/TLS version it supports, the cipher suites (encryption algorithms) it can use, and a randomly generated number for session uniqueness.
2. Server Hello:
   • The server responds with a “Server Hello” message, choosing the SSL/TLS version and cipher suite that both the server and client support.
   • The server also sends its SSL certificate, containing its public key and identity information. This certificate is issued by a trusted Certificate Authority (CA), like DigiCert or Let’s Encrypt.
3. Certificate Verification:
   • The client verifies the server’s certificate with the issuing CA to ensure it’s legitimate and trustworthy.
   • If the certificate is valid, the client proceeds. If it’s not (for example, if the certificate is expired), the browser usually alerts the user with a warning.
4. Key Exchange:
   • After verifying the certificate, the client generates a “session key” and encrypts it with the server’s public key (provided in the certificate). This is the key the client and server will use to encrypt and decrypt data during the session.
   • The server decrypts the session key using its private key.
5. Session Encryption:
   • Now that both the client and server have the session key, they begin using it to encrypt and decrypt data.
   • This encryption ensures that only the client and server can read the data sent back and forth, protecting sensitive information from hackers.
6. Secure Communication:
   • The encrypted connection is now established, allowing secure communication between the client and server.
   • Data exchanged in this session is kept confidential and protected from interception or tampering.

Diagram of the SSL Handshake

Adding a visual helps clarify these steps. Here’s a simplified diagram you could use to show each stage of the handshake: