openssh unix dev - Mar 2006 - HostKey checking and DNS finger print verification

Hello All,

I have a client-server setup with about 100 nodes. We often install the OS 
and this results in change of host keys in our server. This necessiates the 
need to update all known_hosts files in the client machines. Im using the 
VerifyHostKeyDNS option in the client side where the DNS is updated with new 
finger print each time we change the host key. But still the SSH client 
verifies its known_hosts file even the DNS finger print matches.

Is there any way to overcome clients local database checking if DNS finger 
print matches? What are the security issues associated with this way?

Thanks,
Senthil Kumar.

Senthil Kumar wrote:
> I have a client-server setup with about 100 nodes. We often install the OS 
> and this results in change of host keys in our server. This necessiates the
> need to update all known_hosts files in the client machines. Im using the 
> VerifyHostKeyDNS option in the client side where the DNS is updated with
new
> finger print each time we change the host key. But still the SSH client 
> verifies its known_hosts file even the DNS finger print matches.
> 
> Is there any way to overcome clients local database checking if DNS finger 
> print matches? What are the security issues associated with this way?
If your DNS is trusted (ie DNSSEC) then the fingerprints will be trusted
too.  Otherwise the DNS results are used as an additional check but are
not trusted.

If practical you could also save and restore the host keys during a rebuild.

-- 
Darren Tucker (dtucker at zip.com.au)
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usually comes from bad judgement.