What is an RSA host key?

Question

I get this message saying:

Permanently added the RSA host key for IP address '192.30.252.130' to the list of known hosts

What is the meaning of the RSA key and what is the concept behind known hosts?

Answer 1

The RSA key is a private key based on the RSA algorithm. The private key is used for authentication and a symmetric key exchange during establishment of an SSL/TLS session.

So this simply means that the host '192.30.252.130' is now a trusted host (one of known hosts) and you can now have a secured connection with this host. This could be used in multiple cases, like using them for logging into your computer(s) via OpenSSH or other secured shell.

Once you connect to a host and the host key is saved to the known_hosts file, your client uses the key to verify all subsequent connections. The same host key information is on the server as well, in case the host key changes, your client would smell something fishy (maybe a man-in-the-middle attack ) and act accordingly.

Refer to Wikipedia for details of the RSA algorithm and the process.

Also refer to a similar question on Unix and Linux .