> For the complete documentation index, see [llms.txt](https://blog.syselement.com/home/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://blog.syselement.com/home/courses-notes/practical-networking/practical-tls/1-tls-ssl.md).

# TLS/SSL Overview

## Introduction

[**SSL**](https://www.cloudflare.com/learning/ssl/what-is-ssl/) (**S**ecure **S**ockets **L**ayer) and [**TLS**](https://www.cloudflare.com/learning/ssl/transport-layer-security-tls/) (**T**ransport **L**ayer **S**ecurity) are both protocols used to secure internet communication. SSL was the original, but it has largely been replaced by TLS due to security improvements.

By creating a **secure, protected "tunnel" across the Internet**, they encrypt data to keep it private and secure while it's being transmitted between a client (like a web browser) and a server (like a website). TLS is the newer (SSL renamed by IETF), more secure version that's widely used today. The 2 terms are often used interchangeably.

* **HTTPS** - HTTP secured by an SSL/TLS
* SSL VPN for private corporate network
* SSL VPN via public VPN provider

The purpose of SSL/TLS is to protect the data that can be captured.

* **Confidentiality** - data accessible only by client and server - Encryption
* **Integrity** - data is not modified between client and server - **Hashing**
* **Authentication** - client/server are who they say they are - **PKI**

The data put on the wire is still passing through someone else's network.

* **Anti-Replay** - prevents attackers from reusing intercepted data to gain unauthorized access. It provides sequence numbers built in to integrity and authentication mechanism.
* **Non-Repudiation** - ensures parties can't deny their involvement in a transaction or communication.

The key players of the SSL/TLS ecosystem are:

* **Client** - entity initiating the TLS handshake, `e.g.` web browser, apps, IoT, etc
  * optionally authenticated at the SSL layer (rarely provides a certificate)
* **Server** - entity receiving the TLS handshake, `e.g.` web server, etc
  * always authenticated (the user has to know what server he is talking to)
* **Certificate Authority** (CA) - governing entity that issues digital certificates to servers
  * trusted by client and server
  * provides **Trust Anchor** - if the client trusts the CA, it can trust what the CA trusts
  * [CAs organizations](https://w3techs.com/technologies/overview/ssl_certificate): [Let's Encrypt](https://letsencrypt.org/), [IdenTrust](https://www.identrust.com/), [GlobalSign](https://www.globalsign.com/en), [Sectigo](https://www.sectigo.com/), [DigiCert](https://www.digicert.com/), [GoDaddy](https://www.godaddy.com/), ...

## TLS/SSL Versions

* [SSL Guide – The Complete Guide to SSL/TLS Certificates](https://aboutssl.org/ssl-guide/)

![SSL/TLS Versions - aboutssl.org](/files/VTrFwajXzexEV8Hmouwu)

* [Qualys SSL Labs - SSL Pulse](https://www.ssllabs.com/ssl-pulse/)

![Qualys SSL Labs - SSL Pulse](/files/rHs84WdyovabXbU9YC0m)

Security must be balanced with Accessibility, based on the usage case.

* [TLS vs SSL: What's the Difference? Which One Should You Use? - Kinsta.com](https://kinsta.com/knowledgebase/tls-vs-ssl/)

![TLS 1.3 Usage - Kinsta.com](/files/evqNAU8dz7Faz5C4VkDI)

![TLS 1.2 usage - Kinsta.com](/files/zCMn7KSGxFJGGZKh8hug)

**SSL v3.0** (declared insecure as of Oct 2014 due to POODLE attack), as a complete redesign of SSL v2.0 is the foundation of the following TLS versions (TLS 1.0, 1.1, 1.2).

**TLS v1.0**

* Protocol ownership transferred to [**I.E.T.F.**](https://www.ietf.org/)
* almost identical to SSL v3.0
* Vulnerability: BEAST attack on CBC ciphers
* **protocol deprecated** on March 2021

**TLS v1.1**

* deprecated EXPORT grade ciphers
* protection against CBC attacks
* **protocol deprecated** on March 2021

[**TLS v1.2**](https://datatracker.ietf.org/doc/html/rfc5246)

* improved security of key generation
* support for **AEAD** ciphers (**A**uthentication **E**ncryption with **A**ssociated **D**ata)
* secure, recommended

[**TLS v1.3**](https://datatracker.ietf.org/doc/html/rfc8446)

* major changes from prior TLS/SSL versions, favors security and simplicity
* shorted handshake
* **forward secrecy** required
* 0-RTT resumption
* AEAD ciphers required

***