Understanding the TLS Handshake: Unlocking the Secrets Behind Your Secure Connection 🔒

In today’s digital landscape, secure connections are more crucial than ever. We often see that reassuring padlock icon in our web browsers, but what does it truly represent? In this post, we will delve into the intricacies of the TLS Handshake, which establishes your secure connection with a website.

To help illustrate this complex process, we will reference an informative infographic which depicts the various messages exchanged between your web browser (the Client) and the website server (the Server) during a TLS session establishment. For a richer understanding, consider keeping the infographic open in a separate tab while you read through the explanations.

The Purpose of SSL/TLS

Before we get into the handshake details, it’s important to understand the dual objectives of SSL/TLS:

1. ✅ Authentication: Verifying that the server is truly who it claims to be.
2. ✅ Data Security: Establishing session keys to encrypt the data exchanged between the Client and server.

Now let’s break down how the TLS Handshake functions step by step.

Step 1: Client Hello

The handshake kicks off with the Client sending a Client Hello message, which contains five critical fields:

• SSL Version
• Random Number
• Session ID
• Cipher Suites
• Extensions

Each of these components plays a vital role in ensuring a secure connection.

SSL Version

The Client identifies the highest version of SSL/TLS it supports (e.g., SSL 3.0, TLS 1.0, etc.), which the Server also confirms during its response. Presently, only TLS 1.2 and TLS 1.3 are deemed secure.

Random Number

The Client generates a random 32-byte value that adds entropy for creating session keys, enhancing the randomness necessary for encryption.

Session ID

This field is used for session resumption, allowing the Client and Server to bypass the overhead of a full handshake by referencing a previous session if applicable.

Cipher Suites

The Client sends a list of supported Cipher Suites, which specify the algorithms for authentication, key exchange, symmetric encryption, and hashing. The Server will select one of these for the session.

Extensions

Extensions provide additional features that were not part of the original SSL/TLS protocol. For simplicity, we will assume no extensions are included in our example.