[cabfpub] Certificate lifetimes: end state or trajectory?

[Ryan Sleevi]

I doubt the substance of the conversation will change much here - it's an
emergent fact that our organizations have differing expectations of
security, and how much or how little cost we externalize to our users to
achieve that definition.

I can appreciate that CAs are both much more relaxed in their definition -
by virtue of the fact that their goals are not aligned with browsers'
goals, in ways both positive and negative for the ecosystem - and that CAs
are not concerned about those costs, because they are costs they do not
directly bear. So it's very easy to have opinions - that browsers should
relax their expectations of user security, or to accept these costs as
acceptable - but it's rather difficult to actually make that case a
compelling argument, and as such, we're unlikely to make progress.

I'm not sure a police officer, if she pulled me over, would find much
solace in my argument that I wasn't wearing a seatbelt, because I only
planned to crash gently. So too should we be suspicious of arguments that
fail to protect users from attack.

However, I also suspect that this disagreement relates to our fundamental
disagreement about what is a 'valid' attack - and what are 'attacks' for
which CAs are concerned about, but which browsers and site operators are
not.

On Fri, Mar 10, 2017 at 6:06 PM, Ben Wilson via Public <public at cabforum.org>
wrote:

> +1  (Sometimes it depends on the type of crash you're involved in.)
>
> -----Original Message-----
> From: Public [mailto:public-bounces at cabforum.org] On Behalf Of Robin Alden
> via Public
> Sent: Friday, March 10, 2017 3:44 PM
> To: 'CA/Browser Forum Public Discussion List' <public at cabforum.org>; 'Kirk
> Hall' <Kirk.Hall at entrustdatacard.com>; 'Phillip Hallam-Baker'
> <philliph at comodo.com>
> Cc: Robin Alden <robin at comodo.com>
> Subject: Re: [cabfpub] Certificate lifetimes: end state or trajectory?
>
> Adam is cleverer than a whole box-full of the rest of us, but he isn't
> infallible and you cannot quote his blog as incontrovertible fact.
>
> It is not true that it only works when you don't need it.
> It is true that it doesn't always work when you need it, but that is not
> the
> same thing by any manner of means.
>
> > This is because "[A]n attacker who can intercept HTTPS connections [so
> > as to use their bad cert for an MITM] can also make online revocation
> > checks appear to fail and so bypass the revocation checks."
> Maybe.  Maybe not.
> It depends where the attacker is situated.
> If you're in the same coffee shop as him, you're toast.
> If the attacker is sitting in the data center that hosts the site with the
> cert, then the attacker can't touch the path between the client and the CA,
> so you've overstated the case.
>
> The perfect can be the enemy of the good.
>
> Regards
> Robin Alden
> Comodo
>
>
> > -----Original Message-----
> > From: Public [mailto:public-bounces at cabforum.org] On Behalf Of Gervase
> > Markham via Public
> > Sent: 10 March 2017 12:37
> > To: Kirk Hall <Kirk.Hall at entrustdatacard.com>; CA/Browser Forum Public
> > Discussion List <public at cabforum.org>; Phillip Hallam-Baker
> > <philliph at comodo.com>
> > Cc: Gervase Markham <gerv at mozilla.org>
> > Subject: Re: [cabfpub] Certificate lifetimes: end state or trajectory?
> >
> > On 03/03/17 20:34, Kirk Hall wrote:
> > > Gerv - on the issue of revocation checking, not everyone is asking
> > > for browsers to turn on hard fail if the browser fails to get a
> > > response to a revocation query in a reasonable time..  We would be
> > > very happy to continue with soft fail - but please, turn on
> > > revocation checking again.  Even if the browser doesn't get a timely
> > > response in (say) 10% of queries, if it does receive a response
> > > "revoked" in the other 90% of queries, and displays that to users,
> > > that would be a great increase in user security.
> >
> > As noted by Adam Langley, "[S]oft-fail revocation checks are like a
> > seat-belt that snaps when you crash. Even though it works 99% of the
> > time, it's worthless because it only works when you don't need it."
> >
> > https://www.imperialviolet.org/2012/02/05/crlsets.html
> >
> > This is because "[A]n attacker who can intercept HTTPS connections [so
> > as to use their bad cert for an MITM] can also make online revocation
> > checks appear to fail and so bypass the revocation checks."
> >
> > Gerv
> > _______________________________________________
> > Public mailing list
> > Public at cabforum.org
> > https://cabforum.org/mailman/listinfo/public
>
> _______________________________________________
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