Re: Feature request
From: PerlBoy (nu-ff-niet_at_geen-idee.nu)
Date: 10/03/04
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Date: Sun, 3 Oct 2004 10:02:23 +0200
"Darren Tucker" <dtucker@dodgy.net.au> wrote in message
news:cjo2oj$1gq$1@gate.dodgy.net.au...
> In article <cjn7g2$9i$1@news.cistron.nl>,
> PerlBoy <nu-ff-niet@geen-idee.nu> wrote:
> [about ssh private key files]
> >Do I understand it correctly that the file on disk is the private key
minus
> >the passphrase?
>
> No, the private key file on disk is the private key encrypted with the
> passphrase. The private key is (in the case of RSA) just a big number
> corresponding to the numbers representing the public key, stored as a
> binary blob. The passphrase can be changed (ie decrypt then re-encrypt
> the blob) without changing the key ("ssh-keygen -p" for OpenSSH).
>
Thanks for explaning. Now that I understand the working of the private key
and passhrase I also understand that there is no way you can control the
passphrase strength for encrypting the private key. Still it would be nice
if somehow the passphrase strength could be enforced on the server side.
> >Okay, but the passphrase belongs to the private keyfile. I wish we could
> >lock the private key for a known to be strong passphrase.
>
> You can't unless you control the hardware and software accessing the
> private key. This is a "smartcard", and several vendors sell them.
>
> [...]
> >Very good point.... I think the whole private keyfile should be sent. But
> >how do you do that secure?
>
> You do it securely by not doing it. By definition, it is *not* secure.
> It's a terrible idea. A single compromised host could capture the private
> key, conduct an offline attack on the passphrase and compromise *all*
> hosts with the corresponding public key.
>
> >Pity! I really love/hate passphrases. They can be very long and strong
but
> >also very short or empty.... It would be nice if SSH
developers/encryption
> >specialist would take look into this feature request, because if we have
no
> >means of controlling passphrase strengths in the future then I think we
are
> >doomed to switch them of by corporate security :-(
>
> What you're asking for is equivalent to wanting telnetd/login to
> reject passwords if the user writes them down on a sticky-note. It's a
> people/policy problem not a technical problem.
>
> --
> Darren Tucker (dtucker at zip.com.au)
> GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4 37C9 C982 80C7 8FF4 FA69
> Good judgement comes with experience. Unfortunately, the experience
> usually comes from bad judgement.
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