Understanding the TLS Handshake: Unveiling the Magic Behind HTTPS

When you browse a website and see that reassuring little padlock icon 🔒 in your browser’s address bar, you can feel secure knowing that your connection is protected. But what really happens behind the scenes to establish this secure connection? In this article, we will explore the TLS Handshake process, highlighting the vital steps that ensure your data remains safe while you navigate the online world.

To assist in our exploration, you might find this infographic useful: . Having it open in another tab will provide valuable context for our discussion.

The Purpose of SSL/TLS

Before diving into the details of the handshake itself, let’s clarify the fundamental objectives of SSL/TLS:

• ✅ Authentication: Ensures the server is genuinely who it claims to be.
• ✅ Data Protection: Establishes session keys to secure the data transmitted between client and server.

Key Concepts

Before we examine the handshake steps in detail, it’s important to understand two concepts:

• Records vs. Packets: Each line in the infographic represents a “record” transmitted during the TLS handshake, which differs from a packet. Sometimes, multiple records can fit within a single packet, and vice versa.
• Essential Cryptography: To fully grasp the TLS Handshake, it’s helpful to be familiar with key cryptographic concepts such as Hashing, MACs and HMACs, and Encryption.

With those principles in mind, let’s begin to unpack the various components of the TLS Handshake.

Step 1: Client Hello

The handshake process commences with the client (your web browser) sending a Client Hello message. This includes several crucial fields:

1. SSL Version: The highest version of SSL/TLS supported by the client.
2. Random Number: A 32-byte random value to ensure security in key generation.
3. Session ID: Used for session resumption when reconnecting.
4. Cipher Suites: A list of algorithm combinations the client can support