Understanding the TLS Handshake: Navigating to That Coveted Padlock 🔒

In this article, we delve into the intricate process that occurs between your browser and the website you’re visiting to establish a secure connection, signified by that reassuring padlock symbol. 🔒

To enhance your understanding, I recommend viewing the accompanying infographic that visually summarizes the TLS handshake. You can find it here: TLS Handshake Infographic. It serves as a useful reference while we explore each component of the handshake below.

Introduction to TLS Handshake

To begin, it’s essential to understand the primary objectives of SSL/TLS protocols:

• ✅ Verify the identity of the server.
• ✅ Establish session keys to secure data transfers.

Before we dive into the specifics of the handshake, let’s clarify a couple of key concepts:

Records vs. Packets

In the infographic, each line represents a “Record” exchanged during the TLS handshake. It’s important to note that a single Record may be contained within multiple packets, or vice versa.

Fundamentals of Cryptography

Familiarity with basic cryptographic concepts such as Hashing, MACs and HMACs, and Encryption is beneficial for understanding the TLS handshake. However, this article will focus on the handshake itself without diving deeply into these topics. For those who need a refresher, I encourage checking out the linked videos for more information.

With that context, let’s examine the various records that constitute the TLS handshake.

1️⃣ Client Hello

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

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

These elements collectively support the handshake’s objectives.

1️⃣.1 – SSL Version

The Client indicates the highest version of SSL it supports (e.g., SSL 3.0, TLS 1.0, TLS 1.1, or TLS 1.2). The Server responds with its own supported