SSH and GPG Keys

Reto Bachmann-Gmuer reto at gmuer.ch
Wed Jun 1 13:23:25 UTC 2005


Am Mittwoch, den 01.06.2005, 13:37 +0100 schrieb James Wilkinson:
> Stephen R Laniel wrote:
> > The SSH private key is just as secure as the GPG key. The
> > only reason I can think of that it *wouldn't* be as secure
> > is if a lot of people had signed your GPG key. Then when
> > signing into a remote host, the host could check the
> > signature. It's a decent idea, but I've never seen it
> > implemented.
> 
> Actually, it can be *more* secure.
Hmm, as you say later passing the public-key directly if possible even
with GPG, but the web-of-trust stuff is missing in SSH

But I would find it elegant to have one key-pair for SSH/GPG/SSL are
there fundamental barriers making this impossible? 

I've looked at httpsy[1] which basically describes an https-variant
without the need of certificate authorities. I'd like to see this
combined with the mutual key signing of gpg. And I'd like to have one
key wich identifies me as client-certificate when I access a website,
sign an email, open an ssh connection and certifies that my blog is
indeed mine.

reto


[1] http://www.waterken.com/dev/YURL/httpsy/

> 
> Ideally, you should be able to generate a server host key on one
> machine, take a copy of the public key from
> /etc/sshd/ssh_host_*_key.pub, carry it on something like a floppy disk,
> and put it into the ~/.ssh/known_hosts file on the other computer. Then
> you don't have to worry about the "degrees of trust" of a GPG key: you
> *know* that the key was generated on the computer you were interested
> in. So if SSH (or PuTTY) connect to it without complaint, you *know*
> you're connnecting to the right computer. [1]
> 
> You can do something similar with personal keys.
> 
> What's important is to work out what the security is giving you. For
> SSH, what's important is that the remote machine is the one you think it
> is (and that the user is the one the server thinks he or she is). [2]
> It's practical to do something like this for SSH, because most people
> only SSH into a few computers.
> 
> It would be possible to do something like this for GPG if you only ever
> e-mailed a few people. Since that isn't normally the case, the Next Best
> Thing is to establish a "web of trust" so you can be *pretty* sure that
> the person who e-mailed you is who they say they are, even if you've
> never met them.
> 
> James.
> 
> [1] Barring Trojan binaries or stolen keys, at any rate.
> 
> [2] SSH sessions are encrypted anyway, with strong cryptography that
> isn't based on your username, password, passphrase, or key (once the
> connection has been set up). All you have to worry about is "man in the
> middle" attacks, where you're connecting to the wrong computer. That's
> what all the host key business is about.
> -- 
> E-mail address: james | Cardinal Fang: you are hereby charged that you are
> @westexe.demon.co.uk  |                crunchy and good with ketchup.
>                       |     -- The megahal program, trained on my quote file.
> 





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