Learn what SSH (Secure Shell) is, how it provides encrypted communication for managing servers remotely, and why it replaced older protocols like Telnet. This guide covers the basics of its cryptographic handshake and how to connect.
Publish date: 9/15/2025
If you've ever needed to manage a server that isn't sitting right in front of you, you've probably come across SSH. It's the standard tool for remotely accessing and controlling computers over a network, and for good reason.
But what exactly is it, and how does it keep your connection safe?
Before SSH came along in the mid-90s, system administrators often relied on tools like Telnet. The problem was, Telnet sent all information, including your username and password, in plain text. Anyone "listening" on the network could easily intercept your credentials and gain full access to the server. It was clear that a secure alternative was needed, and that's where SSH stepped in.
SSH stands for Secure Shell (or Secure Socket Shell), and it's a cryptographic network protocol for operating network services securely over an unsecured network. That's a technical way of saying it creates a safe, encrypted tunnel for you to send commands to a remote machine.
When you connect to a server using SSH, you get a shell prompt, just like the one you'd have on your local terminal. From there, you can run commands, manage files, install software, and perform any administrative task as if you were physically there. The key difference is that your entire session is encrypted, protecting your credentials and data from being exposed.
The magic of SSH lies in its use of cryptography to establish a secure connection. It doesn't just encrypt everything with a single method; it uses a combination of techniques in a sequence called the SSH handshake. Let's break it down into a few steps.
known_hosts file on your computer. On future connections, your client checks the server's key against the stored version to make sure you're connecting to the same server and not an imposter.Because public key authentication is so much safer, it's one of the first things any administrator should set up. In fact, combining it with other techniques is fundamental to protecting your server, which we cover in our guide on 7 quick and easy ways to secure SSH on a Linux server.
Connecting via SSH is straightforward. On Linux, macOS, or modern Windows, you can just open a terminal and use the OpenSSH client that's already built-in.
The basic command structure is:
ssh username@server_ip_or_hostname
For example, to connect to a server at 192.0.2.1 with the username admin, you would run:
The first time you connect, you'll see a message like this:
The authenticity of host '192.0.2.1 (192.0.2.1)' can't be established.
ED25519 key fingerprint is SHA256:AbCdEfGhIjKlMnOpQrStUvWxYz1234567890abc.
Are you sure you want to continue connecting (yes/no/[fingerprint])?
This is the host key verification step we mentioned earlier. Type yes and press Enter. The server's key will be saved, and you'll be prompted for your password or authenticated with your SSH key.
The default port for SSH is TCP port 22. For security, it's a common practice to change this to a different, non-standard port to reduce exposure to automated bots that scan for open port 22s.
No, they are different protocols for different purposes. SSH is used to create a secure shell for remote administration and file transfers. SSL (Secure Sockets Layer) and its successor, TLS (Transport Layer Security), are primarily used to secure web traffic with HTTPS, as well as email and other application traffic.
Yes. Modern versions of Windows 10 and 11 include a built-in OpenSSH client, allowing you to use the ssh command directly from the Command Prompt or PowerShell. For years, the most popular third-party SSH client for Windows has been PuTTY, which is still a great option. You can also use the Windows Subsystem for Linux (WSL) to get a full Linux environment, which includes SSH.
A password is a secret that you know and send to the server to prove your identity. If it's guessed, stolen, or intercepted on an insecure connection, it can be used by an attacker. An SSH key pair is a set of cryptographic files. You prove your identity by showing you possess the private key, without ever revealing the key itself. This makes it almost impossible to steal through network sniffing or brute-force guessing.
SSH is an essential tool for anyone managing servers. It provides a reliable and secure way to execute commands, transfer files, and maintain your infrastructure from anywhere. Understanding how it works is the first step toward using it effectively and keeping your systems safe.
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