Re: Key Management

From: Richard E. Silverman (slade@shore.net)
Date: 12/14/01 

From: slade@shore.net (Richard E. Silverman)
Date: 14 Dec 2001 12:47:02 -0500

> > We are trying to implement a campus wide ssh installation here at work.
> > I am trying to find if there is any global key management(LDAP, NIS,
> > ...) that can be built into ssh to manage keys.
> >
> > Thanks.
> >
> > Chris
>
> You *shoudln't*. One of the principles of SSH key management, especially of
> the private key, is that it should never leave the user's hands. It
> definitely shouldn't be shared via any broadcast system such as LDAP or NIS
> designed to broadcast *public* information.

If every computer in the world were equipped with a smartcard reader and
all SSH clients could use them, we might come close to this (but even
then, there's nothing to prevent a Trojaned client from using your
smartcard to sign away your firstborn, as well as logging you in
somewhere). But they don't, and we make compromises -- just having your
private key file in your home directory instead is one. As long as the
distribution method is secured so as to resist disclosing the encrypted
private key for a dictionary attack, I wouldn't reject this idea out of
hand.

Besides, Chris didn't say anything about private keys specifically, and
"key management" can mean more than that. The SSH-2 protocol allows
attaching certificates to keys, and the ssh.com server implementation uses
this feature. With it, you can dispense with known-hosts files -- each
client can simply have a trusted copy of a CA certificate under which your
host key certificates are issued. Host keys can be added, changed,
expired (with CRL support) etc. transparently. Of course, this assumes
(currently) that all your clients are also ssh.com software -- but you can
allow other clients to go the traditional route by providing regular host
keys as well.

Another possibility is using GSSAPI/Kerberos with OpenSSH:

  http://www.sxw.org.uk/computing/patches/openssh.html

This also handles server authentication, taking advantage of your existing
Kerberos key management. 

-- 
  Richard Silverman
  slade@shore.net

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