TLS: Explanation & Insights

The term "TLS" refers to Transport Layer Security, a cryptographic protocol designed to provide communications security over a computer network. In this blog post, we are going to dive into the world of TLS, learn how it works, and how to set it up on your own Linux server.

What is TLS?

Transport Layer Security (TLS) is a protocol that ensures privacy between communicating applications and their users on the internet. When a server and client communicate, TLS ensures that no third party may eavesdrop or tamper with any message. TLS is the successor to the Secure Sockets Layer (SSL).

Why is TLS Important?

TLS is important because it helps provide privacy and data integrity between two communicating computer applications. It is typically used for web browsers and other applications that require data to be securely exchanged over a network, such as file transfers, VPN connections, and voice over IP (VoIP).

Understanding How TLS Works

TLS operates by using a combination of symmetric and asymmetric cryptography. Here's a simplified breakdown of how it works:

  • The client sends a "hello" message to the server, indicating that it wants to establish a secure connection.
  • The server responds with a "hello" message of its own, and provides its public key.
  • The client uses this public key to encrypt a pre-master secret and sends it to the server.
  • Both the client and the server use this pre-master secret to generate a session key.
  • All further communication between the client and server is encrypted with this session key.

Typical Problems with TLS

Setting up TLS can sometimes be a challenge, especially for beginners. Some of the typical problems include:

  • Misconfiguration: One of the most common problems is simple misconfiguration, such as forgetting to include a necessary parameter in your nginx or Apache configuration files.
  • Certificate issues: Problems with SSL certificates, such as expired certificates or certificates issued by an untrusted authority, can also cause TLS issues.
  • Compatibility issues: Sometimes, older versions of certain software may not support the latest versions of TLS, which can lead to compatibility issues.

Setting up TLS on a Linux Server

Here's a basic guide on how to set up TLS on a Linux server, using OpenSSL to generate a self-signed certificate.

sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/ssl/private/apache-selfsigned.key -out /etc/ssl/certs/apache-selfsigned.crt

This command generates a new self-signed certificate that is valid for 365 days. The -x509 option tells OpenSSL that we want a self-signed certificate, while the -nodes option tells OpenSSL to skip the option to secure our certificate with a passphrase. We would have to enter this passphrase every time we restart the server, so skipping this option saves us from that headache.

After generating the certificate, you would typically configure your web server to use this certificate for serving HTTPS traffic. The exact steps would depend on your web server software.


TLS is a critical part of secure internet communication and understanding how it works is essential for anyone running a Linux server. While it can be a bit complex to set up, especially for beginners, the security benefits it provides are well worth the effort.

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