The SSH Cryptosystem
In this article you'll see how the SSH cryptosystem provides privacy protection, integrity, and authenticity of data as it traverses a network.
If you're using at least FreeBSD version 4.0, your FreeBSD system uses OpensSSH and it is installed and ready to go. As the name implies, this is an open source implementation of the SSH cryptosystem.
In a previous article I demonstrated that the telnet utility can be used to login to a remote computer from another system. Once logged in, a user can do anything on that remote system as if he were physically sitting in front of it. That is, every keystroke is sent to the remote system and interpreted as if it had come from the keyboard attached to that remote system (even though that keyboard input first had to travel over a network). We also saw in that article that every single keystroke and response was sent in clear text, meaning that a sniffer could watch the entire session.
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