Security of ssh across a LAN, public key versus password

[David Lang]

There is room for differences of opinion here.

other factors
do you reuse the password elsewhere (or use a passwork close enough, most people 
tend to use a static prefix and have a cycling value at the end)

do people use a password manager

do you always start from the same system? or do you use different systems at 
different times. If you use different systems, how do you manage your certs and 
have them in the right place? (can you use a hardware fob to store them, what do 
you do when you forget/lose it, etc)?

is your key passphrase similar to your password?

A cert is a single factor, so is a password. Cert authentication is only two 
factor if you trust that the password is not stored along with the cert (which 
is on the untrusted client)

This is why I push for challenge/response tokens, not simply cert 
authentication, and really wish that FIDO (such as yubikey) was an option, but 
the discussions I've seen about suporting that have not been encouraging.

David Lang

On Mon, 21 Oct 2024, Chris Green wrote:

> I have a small LAN at home with nine or ten systems on it running
> various varieties of Linux.  I 'do things' on the LAN either from my
> dekstop machine or from my laptop, both run Xubuntu 24.04 at the
> moment.
>
> There's a couple of headless systems on the LAN where login security
> is important to me and I've been thinking about the relative merits of
> password and public-key authentication.
>
> Obviously public-key is more secure as regards the actual login
> process but it seems to me that's not really where the vulnerabilities
> are.  If someone 'breaks in' (in the physical or computer sense) to my
> desktop then how might they attack another system on the LAN?  It's
> not physically accessible to them (it's quite a big LAN, one system in
> particular is in another building).  So they can try and guess my
> key's passphrase if I'm using public-key, or they can try and guess my
> password if I'm using password.
>
> It **is** possible to brute force a key passphrase, all the bits you
> need are almost certainly to hand in ~/.ssh.  However I don't think it's
> possible to brute force a password on a remote system, each login will
> take several seconds and you'll get thrown off after very few retries.
>
> My public-key passphrases are going to be similar length and
> complexity to my passwords, they have to be if I'm going to be able to
> remember them.  They are mostly 11 or more characters long with all
> the 'good things' like special characters, mixed case, etc.  Thus I
> suppose they'll be difficult to guess (or brute force). However
> password login can have the same, complex, password strings so I don't
> see how using public-key helps and (as I said above) it seems slightly
> more breakable.
>
> It's also **much** more dificult to keep all those keys etc. well
> organised.  What has brought me to this question is the mixed
> collection of RSA and ed25519 keys all over lots of systems getting
> very difficult to keep under control, and thus error prone (=insecure).
> If I went back to all passwords life would be so much easier!
>
> So, is this right?  It goes against a lot of advice one sees.  Please,
> if I'm talking rubbish please tell me! :-)
>
>