Hi, this is from a discussion I had with Samba developer Andrew
Bartlett. We were discussing usage of the Heimdal kerberos module
hdb-ldap when it turned out that both of us have the same idea on what
to use for - LTSP. 
What do you guys think of the ideas presented here? Has anyone used LTSP
and kerberos together? 

10:29 <tarjei> one of my motivations for doing this is to use it with
linux thin clients
10:30 <tarjei> this means that the box will boot from a nfs root. Do you
think this will pose a problem?
10:30 <abartlet> I see no reason why this cannot work.  This is exactly
what I wish to do with it
10:31 <tarjei> good.
10:31 <abartlet> you will not be able to prove that the KDC is not being
spoofed (as you don't want to put a private key on the workstation NFS
mount)
10:31 <abartlet> but the other servers will certainly tell you...
10:32 <abartlet> (for pam_krb5 I mean.  It can ask for a service key for
the local machine, to detect a spoofed KDC)
10:32 <tarjei> ok, are you planning on doing thin clients in your
environment?
10:32 <abartlet> yes
10:32 <abartlet> not sure of the timeframe, but I do want to do it
10:32 <tarjei> part of the problem might be that kdm (or xdm) runs on
the server
10:32 <abartlet> that's why I wrote the krb5 changes :-)
10:33 <tarjei> two souls same thought
10:33 <abartlet> ok, this is LTSP?
10:33 <tarjei> yes
10:33 <abartlet> ok - that's trivial
10:34 <tarjei> yes ltsp is easy to work with. The plan is to solve the
issues surounding local apps.
10:34 <tarjei> today the suggest you use ssh keys.
10:34 <abartlet> hmm...
10:34 <abartlet> SSH keys, or even gssapi'ed SSH would work
10:35 <abartlet> both would need a private key on the NFS mount
10:36 <tarjei> this is where I expect trouble
10:37 <tarjei> but if you authenticate the user on the nfs'd box,
keeping the keytab in local ram, then maybe you could get around the
issues
10:37 <abartlet> no
10:37 <abartlet> I think you just put the key on the box
10:37 <abartlet> you are already putting the password in-clear over the
network
10:38 <abartlet> for the GDM login
10:38 <abartlet> and if you don't, you can't get 'out' of the server
back to the workstaiton, to start the 'local' app
10:38  * abartlet ponders
10:38 <abartlet> ok, you could run a local GDM, which would secure the
thing quite a bit
10:39 <tarjei> yes that's what I'm saying :-)
10:39 <abartlet> but you would still need the SSH/krb5 private keys, for
the workstations
10:39 <tarjei> didn't you say that pam_krb5 got that?
10:39 <abartlet> local GDM, and the .Xsession being 'ssh -X server
gnome-session'
10:39 <abartlet> you could do this with pam_krb5, and it makes it all
rather secure
10:40 <abartlet> except that it doesn't actually help local apps much
10:40 <abartlet> but the rest is very nicely secure :-)
10:40 <tarjei> this would even imply having secured the link between the
server and the client yes.
10:42 <tarjei> would you mind if the last part of this conversation
(10.29 - > ) was posted to the ltsp list for further comment?
10:42 <tarjei> they might have some ideas.
10:43 <abartlet> that's fine, I've said nothing private here
10:44 <abartlet> I really like the idea of local pam_krb5 and gdm, with
SSH tunnel to the LTSP server
10:44 <abartlet> now, and active attacker can still play a *lot* of fun,
but it locks things down quite a bit...


Tarjei



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