SSH vs Telnet: why one died and one didn't

Telnet came first. It is a protocol for logging into remote machines over a network, and it works by sending everything as plain text. Your username, your password, every command you type, every line the server sends back: all of it travels across the network unencrypted.

In 1995, that was a real problem. Tatu Ylönen, a Finnish researcher, had his university network sniffed by an attacker who collected passwords. He wrote SSH as a direct response, and eventually published it. SSH encrypts the entire session, including the authentication. You cannot read the session by watching the network traffic.

That is the essential difference. Everything else follows from it.

What Telnet is still used for

Telnet is not completely dead. Network engineers use it to test TCP connectivity on specific ports, not because it is secure but because it is simple:

telnet google.com 80

That command tells you whether port 80 is open and accepting connections. Most people use nc or curl for this now, but Telnet still shows up in documentation and old scripts.

Some old embedded systems and network devices ship with Telnet enabled because they pre-date SSH support or the manufacturer never updated the firmware. These are known security problems and generally should not be exposed to the internet.

What SSH does differently

SSH negotiates an encrypted channel before you send any credentials. It also authenticates the server to you using a host key, which prevents a class of attacks where someone inserts a machine between you and your server to intercept the session. The first time you connect to a new server, SSH shows you the host fingerprint and asks if you trust it. If you say yes and the fingerprint changes on a future connection, SSH warns you that something changed.

SSH also handles key-based authentication, which is more secure than passwords. Instead of sending a password, your client proves it has the private key that matches a public key on the server, without ever transmitting the private key itself. See our RSA vs Ed25519 guide for more on how key types compare.

Should you ever use Telnet for remote login?

No. There is no situation where connecting to a live server with Telnet is preferable to SSH. Even on an internal network, password sniffing is possible if any device on that network is compromised.

If you are running a device that only supports Telnet and you cannot install SSH, the right answer is to isolate that device from networks you do not fully control and plan for replacement.

Connecting over SSH from a browser

If you need SSH access from a device that doesn't have a terminal client, SSHDock provides a full SSH client in the browser. It does not support Telnet, which is the correct decision.