How it began
SSH1 and the SSH-1 protocol were developed in 1995 by Tatu Ylönen, a researcher at the Helsinki University of Technology in Finland. Earlier that year his university network had been the victim of a password-sniffing attack, and Ylönen wrote the program for his own use. When beta versions drew attention he saw that it could be put to wider use. In July 1995 SSH1 was released to the public as free software with source code.
Before it existed
At the time, remote login and file transfer tools such as Telnet, rlogin and FTP sent data, including passwords, in plaintext. An attacker who could listen on the network could capture credentials and reuse them, which is what happened on Ylönen's university network.
How it works
SSH sets up an encrypted channel between a client and a server, protecting the confidentiality and integrity of what passes between them. It uses public-key cryptography, so users can authenticate with key pairs. The original protocol, later called SSH-1, was documented by Ylönen as an Internet Engineering Task Force draft in 1995. It had limitations that could not be fixed without breaking compatibility, so an incompatible new version, SSH-2, with new algorithms was introduced in 1996.
How it spread
By the end of 1995 an estimated 20,000 users in 50 countries had adopted SSH1, and Ylönen was receiving 150 email messages a day asking for support. In December 1995 he founded SSH Communications Security to maintain, commercialize and continue developing the software. The IETF formed a working group on the protocol. OpenSSH, a free implementation developed as part of the OpenBSD project, later became the most widely used implementation. SSH is described as the de facto standard for secure access to remote systems, used by system administrators and developers for remote administration, file transfer and tunneling. SSH-2 remains the current version of the protocol.
