Textbook of Linux

b. 1968, Finland — Original author of the SSH protocol and the first SSH implementation

Also known as: Ylönen

Tatu Ylönen designed the SSH (Secure Shell) protocol in 1995 while a researcher at Helsinki University of Technology, after a password-sniffing attack on the university network. His original implementation became SSH 1; the protocol was specified as SSH 2 and later standardised by the IETF as RFC 4250–4256.

Ylönen founded SSH Communications Security Corp in 1995 to commercialise SSH. The original SSH 1 codebase became proprietary, prompting the OpenBSD project under Theo de Raadt to reimplement it as OpenSSH in 1999 — the version now shipped on nearly every Unix-like system.

Ylönen's protocol — not his code — is the enduring contribution: SSH replaced telnet, rlogin, and rsh on the internet and has remained the dominant remote-access mechanism for three decades.