Re: [websec] Alissa Cooper's Yes on draft-ietf-websec-key-pinning-19: (with COMMENT)

[Ryan Sleevi <[e-mail]>]

On Tue, Aug 5, 2014 at 2:27 PM, Alissa Cooper <[e-mail]> wrote:

> Alissa Cooper has entered the following ballot position for
> draft-ietf-websec-key-pinning-19: Yes
>
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> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
>
> I agree with Pete's comment about the first sentence.
>
> It would be nice if in Section 5 or 7 some suggestion could be made for
> UAs to consider the relationship between the functionality they provide
> to clear pins/pinned hosts and the functionality they provide to clear
> (or prevent the storage of) other UA state. E.g., upon clearing one's
> browsing history or entering private browsing mode, it seems like having
> the option to clear pins/pinned hosts or not pin would make sense. This
> is alluded to in Section 7 but not really tied to the threat described in
> Section 5.
>

Just to confirm, you're looking to see an illustrative (non-normative)
example/discussion of UI controls in Section 5, correct?


>
> I'm also curious about whether there is any reason to retain expired
> pins? (Other than the fact that flushing them requires the UA to actively
> check which ones are expired.)
>

I am having a bit of trouble parsing this question. The draft right now
doesn't normatively say one way or the other how to treat expired pins post
expiration. That is, pins are noted, they expire, but there are no
post-expiration steps, since the behaviour is indistinguishable from an
unpinned host.

One reason to avoid proactively erasing pins would be situations of
temporary clock skew, which is, anecdotally, a depressingly common
occurrence. A user who temporarily experienced clock skew would not be
protected from sites they visited during the skew (as pins would be
expired), but could note new pins (following the pinning logic). If the
clock skew was resolved (either manually or through a delayed
reconcilliation, as many modern OSes now go through), the user's original
pins would become viable again (within the expiration window).

This is a client misconfiguration that can't readily be accomodated or
predicted on the server, and it's a complex one, so it seems non-ideal to
document. The observable behaviour, from a server, is that if Client X
attempts to access the Site Y with an expired pin, it's no different than
if they had no Pin. That invariant is retained regardless of which
behaviour the UA implements.