Understanding the TLS Handshake: The Journey to the Secure Padlock 🔒

In today’s digital landscape, the presence of a secure padlock symbol on your web browser indicates that your connection to a website is safeguarded. But what goes on behind the scenes to achieve this security? In this article, we will delve into the intricacies of the TLS (Transport Layer Security) Handshake—the essential process that happens each time you access a secure site.

To enhance your understanding, it may be useful to reference an infographic that outlines the communication between your web browser (the Client) and the web server you are accessing. Consider keeping this image open in a separate tab as you read through the steps below.

Introduction

Before diving into the details of the handshake, it’s crucial to understand the primary objectives of SSL/TLS:

• ✅ Authentication: To verify that the server is indeed the entity it claims to be.
• ✅ Confidentiality: To create session keys that protect the data exchanged during your online sessions.

The handshake comprises various records sent between the Client and the server, and it’s essential to distinguish between records and packets.

Records vs. Packets

Each line in the referenced infographic corresponds to a “Record” in the handshake. It’s important to note that these records are different from packets; multiple records can fit into one packet and vice versa.

Cryptographic Foundations

Familiarity with certain cryptographic terms will help you grasp the complexities of the TLS Handshake:

• Hashing
• MACs and HMACs
• Encryption

We won’t explore these concepts in depth here, allowing us to focus solely on the handshake. However, for those not accustomed to the terminology, resources are available through various educational videos.

With that foundation laid, let’s break down the TLS Handshake step by step!

1️⃣ Client Hello

The TLS Handshake begins with the Client initiating the conversation by sending a Client Hello message. This message contains five vital fields:

1. SSL Version: The highest version of SSL/TLS supported by the Client.
2. Random Number: A 32-byte random value generated by the Client.
3. Session ID: Used for session resumption in future handshakes.
4. Cipher Suites: A list of supported encryption algorithms.
5. Extensions: Additional features that extend the protocol’s functionality.

Each of these components