SSH vs Telnet: Why One Replaced the Other and When Each Makes Sense

If you've ever needed remote terminal access to a server, router, or network device, you've likely used SSH. You might also have encountered Telnet. They accomplish similar things — a text-based session over a network — but they represent completely different eras of computing.

Telnet: Remote Terminals Before Security Mattered

Telnet was designed in 1969 as one of the first internet protocols. Its job is simple: establish a bidirectional byte stream between two hosts so you can run a terminal session. It works, and it's remarkably simple — the protocol overhead is minimal.

The fundamental problem with Telnet is that everything travels in plaintext. Your username, your password, every command you type, and every line of output the server sends — all of it is readable to anyone on the network path between you and the server. In 1969, the ARPANET had a few dozen nodes and was a trusted research network. By the 1990s, this was obviously a disaster.

SSH: Encryption First

SSH (Secure Shell) was created in 1995 specifically to replace Telnet and similar tools. Every byte of an SSH session is encrypted using modern cryptography. Even if someone captures all your network traffic, they see ciphertext they can't read without your private key.

SSH also solves authentication properly. Instead of just sending a password (which could be captured), SSH supports:

• Password authentication — still over an encrypted channel, so the password itself is protected in transit
• Public key authentication — your client signs a challenge with your private key; the server verifies with your public key. Your private key never leaves your machine.
• Certificate authentication — used in larger organisations where SSH certificates are issued by a central authority

SSH also does host key verification. The first time you connect to a server, you get its public key. On subsequent connections, SSH verifies that the key matches what was seen before. If it doesn't — because the server changed, or because someone is intercepting your connection — you get a warning. This protects against man-in-the-middle attacks.

When Is Telnet Still Used?

Telnet still appears in specific contexts where security either doesn't apply or is handled at a different layer:

• Legacy network devices — older routers, managed switches, and industrial equipment often only support Telnet and predate SSH support
• Testing and debugging — Telnet is useful as a generic TCP debugging tool; telnet host port lets you manually send text to any TCP service (checking if port 25 responds, testing an API server)
• Isolated networks — on a completely isolated local network with no external access, the plaintext risk is reduced (though not zero)
• Public services — some intentionally public services (like Telehack, a retro ARPANET simulator) use Telnet because authentication isn't the goal

In Practice

For any server or device you care about, use SSH. The setup is straightforward, the clients are universal, and the security improvement over Telnet is enormous. If you're managing a legacy device that only speaks Telnet, consider whether you can put it behind a VPN or access it only over a network you fully control.

ShellPad supports both SSH and Telnet, with saved connections, key-based authentication, and multiple simultaneous sessions — so you can handle both modern servers and legacy gear from one app.