History of SSH protocol

The first version of SSH protocol (SSH-1) was initially developed by Tatu Ylonen at Helsinki University of Technology, Finland. Tatu Ylonen was a researcher at Helsinki University of Technology. The reason behind the development was a password sniffing attack at the University. The initial purpose of SSH was to find a more secure alternative to TELNET protocol.

SSH is a new protocol compared with TELNET. TELNET was initially developed during late 1960’s. SSH-1 was first released in July 1995. Since the number of SSH protocol users rose to more than 20,000, in December 1995, Tatu Ylonen started a company to provide support for SSH. The name of the company was SSH Communications Security, Inc. The current name of the SSH company at Finland is SSH Communications Security Corp ( Please visit the following link to learn the history of the company, SSH Communications Security Corp.

SSH-2 is the newer version of SSH protocol. SSH-2 was adopted as RFC by Internet Engineering Task Force (IETF) in 2006. The new SSH protocol was named as SSH-2, because the previous version was SSH-1. SSH-2 had many new algorithms and was not compatible with SSH-1 protocol. Some initial RFCs related with SSH-2 are RFC 4250, RFC 4251, RFC 4252, RFC 4253, RFC 4254, RFC 4255 and RFC 4256. Note that, many of the initial RFCs are updated later, with new RFC numbers.

The last free version of the original SSH was 1.2.12. Many restrictions to use SSH came after the last free version of SSH, on its path to become a commercial product. Some OpenBSD developers wanted to make SSH more free. Their work paved the way for OpenSSH (, which is a free implementation of the SSH-2 protocol from the OpenBSD project ( OpenSSH supports both SSH-1 and SSH-2. Please visit following link to view the history of OpenSSH.

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