SSH keys
Read access to .ssh
Having read access over the .ssh directory for a specific user, we may read their private ssh keys found in /home/user/.ssh/id_rsa or /root/.ssh/id_rsa, and we can copy it to our machine and use the -i flag to log in with it:
vim id_rsa
chmod 600 id_rsa
# If ssh keys have lax permissions, i.e., maybe read by other people, the ssh server would prevent them from working.
ssh user@10.10.10.10 -i id_rsa
Write access to .ssh
Having write access over the .ssh directory for a specific user, we may place our public key in /home/user/.ssh/authorized_keys.
But for this we need to have gained access first as that user. With this technique we obtain ssh access to the machine.
This will give us two files: key (which we will use with ssh -i) and key.pub, which we will copy to the remote machine.
Let us copy key.pub, then on the remote machine, we will add it into /root/.ssh/authorized_keys: