SSH
Abbreviation · Development · Origin: 1995
Definitions
SSH, or Secure Shell, is a cryptographic network protocol for establishing secure, encrypted connections between computers over an untrusted network. It replaced insecure predecessors like Telnet and rsh by encrypting all traffic, including passwords and data, between the client and server. SSH is the standard method for remote server administration on Linux and Unix systems, allowing administrators to log in, run commands, transfer files (via SCP or SFTP), and forward network ports through encrypted tunnels. Authentication can use passwords, but public-key authentication is preferred for both security and convenience. SSH also supports agent forwarding, which lets you use your local keys on a remote server without copying them. The most widely used implementation is OpenSSH, included by default in most Linux distributions and macOS. SSH operates on port 22 by default and is an essential tool in every developer's and system administrator's toolkit.
In plain English: A secure way to remotely connect to and control another computer over the internet, like a protected remote desktop for the command line.
Origin Story
Born from a password-sniffing attack on a university network
In 1995, Tatu Ylonen was a researcher at Helsinki University of Technology when a password-sniffing attack hit the university network. Passwords were being transmitted in plain text over Telnet and rlogin, and an attacker was harvesting them by the thousands.
Ylonen decided to write a replacement. In just a few months, he created SSH (Secure Shell), a protocol that encrypted the entire session — passwords, commands, output, everything. He released it as free software in July 1995, and within two years, SSH had an estimated two million users.
Ylonen later founded SSH Communications Security to commercialize the protocol. The free implementation that most people use today is OpenSSH, created by the OpenBSD project in 1999 as a clean-room reimplementation of the protocol. SSH effectively killed Telnet for remote administration and remains the backbone of secure server access.
Coined by: Tatu Ylonen
Context: Helsinki University of Technology, 1995
Fun fact: The OpenSSH project, maintained by a tiny team, secures virtually every server on the internet. It runs on an annual budget smaller than most startups' coffee budget.