Re: SSH Cracking Attempts

From: Jon Dowland (dowland_at_gmail.com)
Date: 09/30/04

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    Date: Thu, 30 Sep 2004 12:15:45 +0100
To: Debian List <debian-user@lists.debian.org>

    On Wed, 29 Sep 2004 16:08:53 -0500, Jacob S <stormspotter@6texans.net> wrote:
    > On Wed, 29 Sep 2004 21:55:59 +0200
    > Matthijs <vanaalten@hotmail.com> wrote:
    >
    > > In the dutch computer magazine C't, I read an article a few months ago
    > > about protecting your computer using a port knocking system. If I
    > > remember correctly, you can close a port (your SSH port, for example)
    > > and only open it when a pre-defined pattern of access attempts on a
    > > pre-defined port (unused for applications) is applied. The SSH port
    > > can then be set to open in your firewall, perhaps only for the
    > > IP-adress that performed the knocking sequence.
    >
    > hmm... You're right, it's not what I'm looking for, but it still sounds
    > like a good concept. I'd be interested in learning more about that, if
    > not for this use with ssh, I have a couple other applications it could
    > work with on servers.

    Quick pro-cons: pro: if a remote root exploit for ssh is found, you
    aren't vulnerable unless the attacker knows your port-knocking code.
    pro-ish: a portscan doesn't show an ssh service running (which you
    might like). cons: you need to have software which supports port
    knocking to open up the port, which you may not have to hand in say
    e.g. a friends house, an internet cafe. con: depending on
    implementation, you might be vulnerable to exploits in the
    port-knocking daemon (so a tradeoff with the first pro). 

    -- 
Jon Dowland
dowland@gmail.com
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