[kwlug-disc] Tightening up SSH

Johnny Ferguson hyperflexed at gmail.com
Mon Jul 19 08:37:38 EDT 2010

I'm relatively new to SSH, though I've come to love it very quickly.

Recently I've been seeing a lot of activity in /var/log/auth.log (of the 
sshd sort). Sometimes 5 straight hours of brute force attacks. I've 
currently only whitelisted a single user. While I feel reasonably safe 
and nothing has cracked yet, I live in constant fear of my account 
getting cracked open, at which time it would take no more than:

sudo rm -rf /

SO, just wondering what advice anyone could offer on hardening SSH. I 
might be a little paranoid, but I think it's still in the range of being 


P.S. How do 2 machines determine an encryption key and communicate this 
to eachother without giving the key away? Are there any good articles on 
how SSH works and what potential vulnerabilities are?

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