Ssh

Introduction to SSH Hardening

Securing SSH access is a no-brainer for any Linux administrator. One effective way to harden SSH access is by using mandatory SSH keys and disabling password authentication. I’ve seen this go wrong when people don’t take the time to set it up properly, so let’s walk through the process.

Understanding SSH Keys

SSH keys are a pair of cryptographic keys used for authentication. The private key is stored on the client machine, while the public key is stored on the server. When a user attempts to connect to the server, the client uses the private key to encrypt a message, which is then decrypted by the server using the public key. If the decryption is successful, the user is granted access.

Introduction to SSH Server Certificate Verification

As a Linux user, you’re probably no stranger to Secure Shell (SSH) and its importance in securely accessing remote servers. With the rise of SSH server certificates, I’ve seen this go wrong when not properly verified - it’s crucial to ensure the authenticity and integrity of your SSH connections. In this article, we’ll explore how to use OpenSSL to verify SSH server certificates on Linux clients.

Introduction to SSH Hardening

I’ve seen many Linux systems compromised due to weak SSH security, so I want to share my approach to hardening SSH access. As of 2026, SSH remains a vital tool for system administration, development, and self-hosting, but its widespread use also makes it a common target for brute-force attacks and unauthorized access attempts. To mitigate these risks, I recommend using Fail2Ban and Public Key Authentication to secure SSH on Debian-based systems.

Introduction to OpenSSH Certificates

I’ve seen many Linux admins struggle with managing SSH keys for their users. OpenSSH certificates are a game-changer here - they offer a more secure and convenient way to manage access to your Linux servers. By using certificates, you can avoid the hassle of managing individual SSH keys for each user and reduce the risk of key compromise.

Generating a Certificate Authority

To get started with OpenSSH certificates, you need to set up a Certificate Authority (CA). The CA will be used to sign and verify the certificates. I usually start with generating a CA key pair using the following command:

Introduction to SSH Hardening

Securing your SSH server is one of the most critical tasks as a Linux administrator. I’ve seen this go wrong when systems are left vulnerable to unauthorized access. The recent high-profile vulnerabilities discovered in popular SSH implementations in 2025 serve as a reminder to keep your SSH server up to date and configured securely. In this article, we’ll discuss practical steps to harden your SSH server without making it overly restrictive.