Understanding the TLS Handshake: Unlocking the Secrets Behind Secure Connections
In today’s digital landscape, the presence of a small padlock icon in your browser symbolizes trust and security. But have you ever wondered what happens beneath the surface to establish that secure connection? In this blog post, we will delve into the intricate process of the TLS (Transport Layer Security) handshake, the critical step that ensures safe communication between your web browser and the websites you visit.
To enhance your understanding, it might be useful to refer to an informative infographic detailing the messages exchanged during a TLS session. You can find the graphic here. Consider keeping this image open in another tab as we explore the handshake process.
Introduction
Before we dive into the handshake itself, let’s acknowledge that the primary objectives of SSL/TLS are twofold:
- ✅ To authenticate the server’s identity.
- ✅ To generate session keys that secure the data exchanged during the session.
Key Concepts to Note
As we navigate the TLS handshake, it’s important to clarify two fundamental aspects:
Record vs. Packets
Each entry in the infographic corresponds to a “record” in the TLS handshake. It’s essential to distinguish these records from packets; multiple records can be encapsulated within a single packet, or a single record might span several packets.
Cryptographic Principles
To fully appreciate the details of the TLS handshake, some background in cryptography will be beneficial. Key concepts include:
While this post won’t dive deeply into these concepts, familiarity with them will enhance your comprehension of the handshake procedure.
Now, let’s dissect the records that comprise the TLS handshake.
1️⃣ Client Hello
The handshake commences with the client sending a Client Hello message. This message includes five pivotal fields:
- SSL Version
- Random Number
- Session ID
- Cipher Suites
- Extensions
Each of these components plays a significant role in achieving the handshake’s goals.
1️⃣.1 — SSL Version
The client identifies the highest SSL/TLS
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