SecureCRT® supports two versions of the Secure Shell protocol. What's the difference between SSH1 and SSH2?

The SSH protocol has two generations: SSH, the initial draft protocol dating to 1995, which is now labeled SSH1, and SSH version 2, usually called SSH2, which was first published in 1998. SSH2, the current version of the Secure Shell protocol, was developed under the Internet Engineering Task Force (IETF) Secsh working group.

SSH1 was developed through 1998, when the technical focus on security issues and optimization shifted to SSH2. The SSH2 protocol was a complete reconception of the protocol and is intended to remove limitations in SSH1, such as the absence of message authentication codes (MACs). The SSH1 draft documentation is not part of the IETF process, and does not match the current SSH1 server implementations. SSH1 has a significant installed base, particularly among early adopters of Secure Shell, and has a more open server licensing for some organizations. However, the maturity and improved security of SSH2 make it VanDyke Software's preferred protocol.