SSH

Notifying the Users of the Host Key Change

Administrators that have other users connecting to their server should notify the users of the host key change. If you do not, the users will receive a warning the next time they connect because the host key the users have saved on their disk for your server does not match the host key now being actually provided by your server. The users may not know how to respond to this error.

You can run the following to display a fingerprint of your new public host key which you can provide to your users via some unalterable method (for example, by a digitally signed e-mail or by displaying the fingerprint on a secured bulletin board):

$ /opt/tectia/bin/ssh-keygen-g3 -F hostkey.pub

When the users connect and receive the error message about the host key having changed, they can compare the fingerprint of the new key with the fingerprint you have provided to them, and ensure that they are connecting to the correct sshd2 daemon. Inform your users that they should notify you if the fingerprints do not match, or if they receive a message about a host key change and do not receive a corresponding message from you notifying them of the change.

This procedure can help ensure that you do not become a victim of a man-in-the-middle attack, as your users will notify you if the host key fingerprints do not match. You will also be aware if the users encounter host key change messages when you have not regenerated your host key pair.

If you want to avoid the risk associated with the first connection, you can do one of the following: