Hardening your Pinebook Pro

[Arwen]

One other thing that probably should be done, is re-create the host SSH keys. SSH host keys should be unique per host. From what I can tell, the default Debian comes with host SSH keys already created from July 11, 2019;

Code:

# ls -l ssh_host_*
-rw------- 1 root root  668 Jul 11 16:55 ssh_host_dsa_key
-rw-r--r-- 1 root root  609 Jul 11 16:55 ssh_host_dsa_key.pub
-rw------- 1 root root  227 Jul 11 16:55 ssh_host_ecdsa_key
-rw-r--r-- 1 root root  181 Jul 11 16:55 ssh_host_ecdsa_key.pub
-rw------- 1 root root  411 Jul 11 16:55 ssh_host_ed25519_key
-rw-r--r-- 1 root root  101 Jul 11 16:55 ssh_host_ed25519_key.pub
-rw------- 1 root root 1675 Jul 11 16:55 ssh_host_rsa_key
-rw-r--r-- 1 root root  401 Jul 11 16:55 ssh_host_rsa_key.pub

Plus, remove the in-secure DSA host key.


Here is how to do it.
As user "root", simply run the following commands. If you like, you can put the hostname in the comment, like "MyHost rsa hostkey".

Code:

cd /etc/ssh
rm ssh_host_*
ssh-keygen -t 4096 -t rsa -C "rsa hostkey" -f ./ssh_host_rsa_key
ssh-keygen -t 521 -t ecdsa -C "ecdsa hostkey" -f ./ssh_host_ecdsa_key
ssh-keygen -t ed25519 -C "ed25519 hostkey" -f ./ssh_host_ed25519_key

Note that you will be asked for a passphrase. Per SSH manual page, host keys must have an empty passphrase. Simply hit return when prompted, (twice per key).