Ubuntu / Debian Linux Regenerate OpenSSH Host Keys
Q. How do I regenerate OpenSSH sshd server host keys stored in /etc/ssh/ssh_host_* files? Can I safely regenerate ssh host keys using remote ssh session as my existing ssh connections shouldn't be interrupted?
A. To regenerate keys you need to delete old files and reconfigure openssh-server. It is also safe to run following commands over remote ssh session. Your existing session shouldn't be interrupted.
Step # 1: Delete old ssh host keys
Login as the root and type the following command:
# /bin/rm /etc/ssh/ssh_host_*
Step # 2: Reconfigure OpenSSH Server
Now create a new set of keys, enter:
# dpkg-reconfigure openssh-server
Sample output:
Creating SSH2 RSA key; this may take some time ... Creating SSH2 DSA key; this may take some time ... Restarting OpenBSD Secure Shell server: sshd.
Step # 3: Update all ssh client(s) known_hosts files
Finally, you need to update ~/.ssh/known_hosts files, otherwise everyone will see an error message:
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that the RSA host key has just been changed. The fingerprint for the RSA key sent by the remote host is f6:67:01:41:e6:20:06:4b:4b:fa:4b:c1:f1:45:45:e0. Please contact your system administrator. Add correct host key in /home/vivek/.ssh/known_hosts to get rid of this message. Offending key in /home/vivek/.ssh/known_hosts:12 RSA host key for 202.54.xx.abc has changed and you have requested strict checking. Host key verification failed.
Either remove host fingerprint or update the file using vi text editor.
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Tags: dpkg-reconfigure command, fingerprint, host identification, host key, host keys, hosts files, man in the middle attack, openssh, rm command, secure shell, server host, shell server, ssh client, ssh connections, ssh session, system administrator
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