Re: [secdir] dir review of draft-laurie-pki-sunlight-05

Ben Laurie <benl@google.com> Wed, 30 January 2013 10:15 UTC

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Date: Wed, 30 Jan 2013 10:15:09 +0000
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From: Ben Laurie <benl@google.com>
To: Jeffrey Hutzelman <jhutz@cmu.edu>
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Cc: The IESG <iesg@ietf.org>, draft-laurie-pki-sunlight.all@tools.ietf.org, "secdir@ietf.org" <secdir@ietf.org>
Subject: Re: [secdir] dir review of draft-laurie-pki-sunlight-05
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On 29 January 2013 21:28, Jeffrey Hutzelman <jhutz@cmu.edu> wrote:
> On Tue, 2013-01-29 at 11:35 +0000, Ben Laurie wrote:
>> On 24 January 2013 19:06, Jeffrey Hutzelman <jhutz@cmu.edu> wrote:
>> > Similarly, as an anti-spam measure, this document proposes that logs accept
>> > only certificates which chain back to a known CA, and requires that logs
>> > validate each submitted certificate before appending it to the log.  This
>> > sounds good, but it's not the only possible mechanism, and so I think MUST
>> > is too strong here.  Additionally, there is no discussion of the security
>> > implications if a client depends on a log to do this and the log does not
>> > actually do so.  Rather than requiring that logs validate every submitted
>> > certificate, the document should only RECOMMEND that they do so, and make
>> > clear that clients MUST NOT depend on such validation having been done.
>>
>> On second thoughts, whilst that is an effective anti-spam measure, it
>> is also part of the functionality of CT: i.e. to identify misissue and
>> give some means to do something about it. The CA check ensures we have
>> someone to blame for misissue.
>
> Hrm.  I sort of thought the idea was for the logs to be untrusted
> repositories, able to be audited but not themselves expected to detect
> problems.  If logs are expected to do validation of this sort, is there
> a way for a third party to discover whether they are doing so (or at
> least, whether they are accepting certificates they shouldn't)?

A third party can indeed verify this - they just watch the log like
any monitor does.

>> I am not averse to suggestions that achieve the overall aim, but I
>> don't see the virtue of leaving it vague in the description of the
>> experiment we are actually running.
>
> I'm not suggesting vagueness; rather, I'm merely suggesting downgrading
> a MUST to a SHOULD, which is still quite strong.  What happens if
> someone wants to start logging certs issued by a private CA, or
> self-signed certs they have observed, or...?

I don't see an issue with logging certs from a private CA. As for
self-signed certs, I don't see the point, but I guess if someone
figures out a point we can relax it in the next version.

> I'm suppose I'm OK with keeping the scope narrower than that for
> purposes of the experiment, as long as it is possible to relax the
> requirement later without breaking the system.  Hence the importance of
> making it clear that clients must not rely on logs to have done
> validation (on which point I think we've already reached agreement).

Cool.