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Date:      Mon, 12 Apr 1999 10:47:29 -0500
From:      David McNett <nugget@slacker.com>
To:        freebsd-security@freebsd.org
Subject:   Re: ssh and scp
Message-ID:  <19990412104729.A62365@dazed.slacker.com>
In-Reply-To: <Pine.BSF.3.96.990409100127.23278B-100000@zerlargal.humbug.org.au>; from Bruce Campbell on Fri, Apr 09, 1999 at 10:26:24AM %2B1000
References:  <199904080936.TAA11475@atdot.dotat.org> <Pine.BSF.3.96.990409100127.23278B-100000@zerlargal.humbug.org.au>

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On 09-Apr-1999, Bruce Campbell wrote:
> Works for me, although I'll admit to being a bit shy of null-password RSA
> keys, which can be alleviated somewhat by restricting which hosts can use
> which keys.

Actually the level of restriction can be much more granular than simply
permitting and denying on a host-by-host basis.  The sshd manpage has
considerable detail on this under the subheading AUTHORIZED_KEYS FILE FORMAT.

In addition to specifying valid remote hosts on a key basis, one can also 
restricte a keypair to a single command with the "command=" directive.

In this way you can prohibit the null-passphrase RSA key to a single task
and not worry about an open shell if the keypair is compromised.

While any null-passphrase situation is by definition an open door, you can
at least limit the scope of the activity that compromise permits.

   from="trust.slacker.com" no-pty no-agent-forwarding no-X11-forwarding
   no-port-forwarding command="/home/luser/bin/only_this_command" 1024 35
   1385747740706965662979092265453243173821775069593500592656102528164588
   1458968562818828612328348480183921191882598263470247545000152074356254
   7885213846674971276953111134546999143676911041828605560207201262339416
   9160927998516632223127781986085086932733750776793503721007278947326141
   39818692207780079452547982359 null passphrase key



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