[cabfpub] Revisiting CAA

Sat May 3 16:28:07 UTC 2014

Well put, Ryan – but I would point out that the “variety of requests for confirmation from CAs that we [Google]  do not do business with about the legitimacy of certain requests” you mention below sound like the results of the vetting process itself – and the vetting process appears to be working well at filtering out illegitimate requests.   Why add yet another step?

No one can identify any mis-issued certs from the past decade that would, in fact, have been prevented by CAA.  Current vetting practices are working.  They can be strengthened if needed, but until we find cases of CA mis-issuance after vetting, the current practices seem to be working well.

CAA clearly is an impediment to competition among CAs, and imposes another administrative and engineering burden on cert issuance.  And yet there are no real business rules around what to do with a contrary CAA result after completion of all vetting for a cert request (using a third party confirmed phone number to call “Google, Inc.,” checking WhoIs, etc.  I can predict with confidence that many large organizations will lose track of who is maintaining the CAA records in various hosting locations, and how to make a change.  The CAA record will then become inaccurate and out of date.  Someone who is authorized to buy certs for a company then signs a deal with a new CA (at a better price and service level), but the contrary CAA record is found.  Either the parties ignore the record as “something we’ll clean up later” or the deal is delayed or prevented because no one can get the CAA record updated.  Either way, after proper vetting of a cert request by an organization the CAA record is not very useful.

CAA strongly favors incumbent CAs, for little or no demonstrated value to the security structure (especially as each CA gets to craft its own response or non-response to a CAA record).  It also lacks DNS support.  To me, it has more potential negative aspects than positive.

From: Ryan Sleevi [mailto:sleevi at google.com]
Sent: Friday, May 02, 2014 6:15 PM
To: Kirk Hall (RD-US)
Cc: Gervase Markham; public at cabforum.org
Subject: Re: [cabfpub] Revisiting CAA

Kirk,

Your parenthetical comment leaves me believing you still do not see the significant value of CAA. Allow me to attempt to explain.

Considering that, at it's most basic level, a certificate is a binding to a DNS record - which is a perfectly acceptable form of validating the legitimacy of the request (according to the BRs), there is no entity more authorized to make decisions on certificate purchases than the DNS operator.

At Google, we have received a variety of requests for confirmation from CAs that we do not do business with about the legitimacy of certain requests. It's not uncommon to see these requests generated by acquisitions, but can also be generated inhouse. There are several means for an applicant to satisfactorily demonstrate control without the involvement of the DNS operator - Options 1, 6, and 7 of Section 11.1.1 of BRs 1.1.7. While these requests are not in line with our internal policies, they are made, and CAs receive them, and with respect to the BRs, they are "valid requests".

Because Google is (fortunately?) a high-value target, such requests are (almost always, unfortunately) deemed High Risk Requests (Section 11.5), and thus either those of us involved in the CA/B Forum, or our Security team, or our DNS operations team will receive a confirmation of the request - for which we always respond "NO"

CAA - if it is actually respected - would allow us to centrally announce our issuance policies (since we centrally manage the DNS for these acquisitions), and potentially avoid this entirely. Of course, that's assuming the CA is concerned about safety and reputation and performs meaningful actions with such signals (eg: treating as a high risk request).

Now, for all the other organizations - whether they be smaller, larger, or the same size as Google - who deal with these same problems (again, Options 6 and 7 are huge enough holes that any competent social engineering/sob story could drive right through) can benefit, even if they're not already on the CA's high risk target list.

In my view - every one of those requests (... including those that were, unfortunately, satisfied) - would count as a misissuance. Unfortunately, because we lack solutions like CT in active deployment, it's hard to quantify those - and even harder, since those most affected by it neither participate nor have a voice here.

On Fri, May 2, 2014 at 5:54 PM, kirk_hall at trendmicro.com<mailto:kirk_hall at trendmicro.com> <kirk_hall at trendmicro.com<mailto:kirk_hall at trendmicro.com>> wrote:
Another concern we have with CAA (apart from the fact that it would not have avoided any known cases of certificate mis-issuance in the past) is that often in larger companies (the most typical fraud targets), the person who buys the certs is not the person who manages the DNS -- and often, the person who buys the certs doesn't even know who is managing the DNS.

Gerv -- at one point, you were going to conduct a test within Mozilla on this point -- how easy/hard was it to get CAA notations put in the proper DNS records, and how easy was it to coordinate the buyer(s) of certs for Mozilla with the various people in charge of the DNS for Mozilla's websites.  As I recall, you found it somewhat difficult to discover and coordinate the two groups.  Is that correct?

-----Original Message-----
From: Phillip Hallam-Baker [mailto:philliph at comodo.com<mailto:philliph at comodo.com>]
Sent: Friday, May 02, 2014 10:54 AM
To: Gervase Markham; Kirk Hall (RD-US); Rick Andrews; public at cabforum.org<mailto:public at cabforum.org>
Subject: Re: [cabfpub] Revisiting CAA

Gerv makes a good point. But I will point out that the reason the CAA spec says nothing about what the CA has to do in response to a non-compliant request is that the IETF is the wrong forum to discuss such issues.

What approaches are appropriate are going to depend on takeup by the domain name holders and what attacks we see. those will change over time. So CABForum is a better place to discuss such issues.

-----Original Message-----
From: Gervase Markham
Sent: Friday, May 02, 2014 11:54 AM
To: kirk_hall at trendmicro.com<mailto:kirk_hall at trendmicro.com> ; Rick Andrews ; public at cabforum.org<mailto:public at cabforum.org>
Subject: Re: [cabfpub] Revisiting CAA

On 02/05/14 16:40, kirk_hall at trendmicro.com<mailto:kirk_hall at trendmicro.com> wrote:
> Can anyone identify one case -- even one -- of mis-issuance of a
> certificate by a CA that would have been prevented by CAA?  (I can't
> think of one.)

It depends how CAs implement CAA. If the CA implements CAA as, among other things, a separate automated sanity check on all certificates, just before they go out the door, using an isolated system - and certs which fail have to be manually approved - then I can see it catching several of the recent misissuances.

If the CA implements CAA as a printed warning on the certificate issuance screen that the operator can choose to deal with or ignore, I imagine it would catch fewer misissuances.

Gerv
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