Laurie: Improving SSL certificate security [LWN.net]

Laurie: Improving SSL certificate security

Posted Apr 6, 2011 20:31 UTC (Wed) by jthill (subscriber, #56558)
In reply to: Laurie: Improving SSL certificate security by djao
Parent article: Laurie: Improving SSL certificate security

So to go for brevity at the expense of putting it too crudely, the basic idea is that any user too dull to be suspicious of a new key isn't going to have enough brainpower to understand any explanation anyone can offer. Looked at that way, I'd call the new-site-new-key warnings that browsers pop now "unnecessary drama" (which I think is accurate, and doesn't dilute the other term). It's the most common situation for getting a new key and the least likely to be a sign of trouble, so fer cryin out loud just install the thing and maybe post a diffident "It doesn't appear you've used this site before from this browser. As an [identifier] they offered [this]; I'll remember it as theirs from now on. [OK]" For changed keys, put enough stutter-steps in the procedure that if they do have the wit to be suspicious they might even click the "How do I know this isn't an impostor?" button in the UI for that.

Yes? I think that's a very good point, now I just hope it's yours and I understood your reasoning correctly.

I think getting that done would have to be a matter of just doing it -- the political opposition to offering an alternative to CAs would be fierce. How hard would it be to maintain a patch getting mozilla or chromium to act this way?

Laurie: Improving SSL certificate security

Posted Apr 7, 2011 11:50 UTC (Thu) by tialaramex (subscriber, #21167) [Link] (5 responses)

The Microsoft research found (I am paraphrasing but you should be able to find it easily enough) that users basically ignore everything except a hard stop.

Red or missing icons, "Are you sure?" messages, changed site layout, missing authentication steps, none of those clue in the ordinary users Microsoft studied that something is wrong. A Firefox-style full-page warning which requires considerable extra steps tugs at them slightly, but not enough to stop most from continuing to enter valuable financial details.

Users don't have the sophistication we assume in our security designs. Even in djao's much simplified system.

SSH works better mostly because it's used by more technical users. Boring, but true.

Any system that doesn't have a hard stop won't be effective. The response to any validation failure, security problem, error etc. has to be "You can't view that website". No "If you're really sure click this" because every single ordinary user will click the button for an easier life. It's just human nature.

Laurie: Improving SSL certificate security

Posted Apr 7, 2011 15:09 UTC (Thu) by djao (guest, #4263) [Link] (2 responses)

To be clear, OpenSSH and the official SSH clients (with strict host checking on, which is the default setting) do come to a full stop when they detect a key change, and this is what I recommend. You have to run a separate program (ssh-keygen with the -R option), or hand-edit the authorized_keys file using a text editor, and delete the offending cached entry in order to connect. The ssh client's error message does not tell the user how to do these things, so you have to know it already, or look it up in man pages etc., something that a non-technical user will not do. (Other SSH implementations handle this differently.)

Although there are obviously legitimate reasons for key changes, on balance they should be rare, unusual events. (Cryptographers will scream and protest, since frequent key changes lead to more interesting problems, more research grants, etc., but let's face it, real world users operate under different assumptions and have different needs.) Let's provide the correct incentives to achieve the optimal balance, rather than the current system which encourages frequent and superfluous key changes.

It is true that SSH has a more technical userbase, and that even the simplest system that I can think of is still too complex for regular users. But this is hardly a reason to support the current certificates system.

Laurie: Improving SSL certificate security

Posted Apr 7, 2011 16:38 UTC (Thu) by nybble41 (subscriber, #55106) [Link] (1 responses)

Cached SSH host keys are stored in known_hosts, not authorized_keys. The latter file is where you put the public keys used to identify SSH clients instead of, or in addition to, password authentication.

Laurie: Improving SSL certificate security

Posted Apr 7, 2011 16:58 UTC (Thu) by djao (guest, #4263) [Link]

Oops, yes, typo (or thinko). The rest of my post is accurate to my knowledge.

Laurie: Improving SSL certificate security

Posted Apr 7, 2011 17:27 UTC (Thu) by jthill (subscriber, #56558) [Link]

I think that makes the division of responsibility pretty clear. Why users behave that way is a research question. That there's limits to what a browser can do to keep them safe is established.

But I don't see how it affects the observation that CAs don't help in either case. Keeping the CA infrastructure is abdicating real responsibility in pursuit of an illusory one. Either way, the real security theater is here, not with any onoz.gif warnings.

And SSH might work better because of what djao said: it does exactly what the research says is necessary. It refuses to connect on a key mismatch.

Laurie: Improving SSL certificate security

Posted Apr 21, 2011 12:36 UTC (Thu) by robbe (guest, #16131) [Link]

My company uses a SSL MITM to do virus scanning of https streams. This poses other problems, but a nice feature is that whenever this MITM proxy can't validate a certificate (expired, no link to a trusted root), the user just gets an error page. No simple way around it, the only option is to call an admin, who will do some serious vetting (hopefully!) of the cert, and maybe put it on the exception list.