5 Best Free and Open Source Tools for SSH Intrusion Prevention
SSH was designed as a replacement for Telnet and for unsecured remote shell protocols such as the Berkeley rsh and the related rlogin and rexec protocols. Those protocols send information, notably passwords, in plaintext, rendering them susceptible to interception and disclosure using packet analysis. The encryption used by SSH is intended to provide confidentiality and integrity of data over an unsecured network, such as the Internet.
There are many ways to make a server running SSH more secure. Here are some examples: Disable root logins, use private key authentications (rather than ssh passwords), enable two-factor authentication, change the port used by SSH, don’t listen on every interface, limit users’ SSH access, and make sure the operating system is kept up-to-date.
There are more steps you can take to harden the server. This article recommends open source software that employ different techniques to make it harder for a server running SSH to be compromised.