Re: S/Key & OPIE Database Vulnerability

From: Eivind Eklund (eivindat_private)
Date: Thu Jan 27 2000 - 02:36:39 PST

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    On Wed, Jan 26, 2000 at 11:53:05AM -0800, Steve VanDevender wrote:
    > Ultimately I wonder how much of a future S/Key has now that SSH and
    > similar utilities are widely deployed and provide much more
    > sophisticated protections, especially session encryption.
    
    S/key is still useful, even when you do use SSH.  By using S/Key, you
    can avoid replay attacks if somebody compromise a workstation or
    temporarily compromise the server (ie, you are secure after reinstall
    and moving skeykeys over.)
    
    You don't get the same effect by using ssh RSA authentication, partly
    you either have
    (1) Users that key in the passphrase each time they connect to the
        server
    OR
    (2) Agent forwarding, which means that if any computer they have an
        account on is compromised, so is your box.  Without any logging in
        their end.  Without any *possibility* of proper logging in their
        end, as the authentication challenges do not themselves contain
        any authentication.
    OR
    (3) Extremely clued users, who either remember to type -a on all ssh
        connections, don't have agent forwarding at all (disabled for the
        machine), or has patched ssh to add the -A keyword (now default
        included in Debian, and possibly in OpenSSH)
    
    Eivind.
    



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