[cabfpub] Profiling OCSP & CRLs

Thu May 11 07:02:32 MST 2017

Certainly the risk profile is greater for long-lived CRLs and long-lived OCSP responses than it is for long-lived OCSP responder certificates, since CRLs and OCSP responses could be replayed to hide a subsequent revocation without compromising the CA’s infrastructure, whereas doing bad things with a long-lived OCSP responder certificate would require the private key of the OCSP responder certificate to be compromised.

So the most obvious suggestion to me is that we should have the same key protection requirements (e.g. HSMs) for OCSP responder keys as for online CA keys, at least for OCSP responder certificates with lifetimes over a certain threshold.  In that scenario, I don’t see a disadvantage to allowing validity that matched the lifetime of the CA itself, since the responder is no more vulnerable than the CA (assuming it’s an online CA.)

I recognize that there’s still a gap in security level for offline CAs though, in that their responders are at the security level of an online CA.  That’s the harder problem.  But addressing it with shorter validity requirements pushes a CA towards making their offline roots easier to access, which could cause more security harm than good.  Perhaps we could allow pre-production of a year’s worth of shorter-validity OCSP responder certificates as a mitigation against this without requiring the offline CAs to be accessed more frequently?  To get value out of this approach, though, the not-yet-in-service responders would need to be protected differently than the in-service one, so we’d need to come up with some rules around that to strike a balance between operational feasibility and security.

From: Public [mailto:public-bounces at cabforum.org] On Behalf Of Ryan Sleevi via Public
Sent: Wednesday, May 10, 2017 4:58 PM
To: CA/Browser Forum Public Discussion List
Cc: Ryan Sleevi
Subject: Re: [cabfpub] Profiling OCSP & CRLs

I'm not trying to disagree here, but I'm trying to find out how we can best specify reasonable expectations.

That is, there's a lot - a *lot* - that can go wrong with 1 year OCSP responders/CRLs. So if we're going to allow them, we need CAs to think about the technical risks and make proactive suggestions on how best to codify that. Because just a blanket "1 year responder" can go very wrong

On Wed, May 10, 2017 at 4:40 PM, Ben Wilson via Public <public at cabforum.org<mailto:public at cabforum.org>> wrote:

I agree that a one-year validity for OCSP Responders / CRLs is a reasonable timeframe for off-line CAs.

Ben Wilson, JD, CISA, CISSP

VP Compliance

+1 801 701 9678<tel:(801)%20701-9678>

From: Public [mailto:public-bounces at cabforum.org<mailto:public-bounces at cabforum.org>] On Behalf Of Doug Beattie via Public
Sent: Wednesday, May 10, 2017 11:15 AM
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Cc: Doug Beattie <doug.beattie at globalsign.com<mailto:doug.beattie at globalsign.com>>

Subject: Re: [cabfpub] Profiling OCSP & CRLs

There are CAs that are kept off-line other than roots, so perhaps the requirement should apply to all “off-line” CAs, assuming we can come to agreement on what that means.

Doug

From: Public [mailto:public-bounces at cabforum.org] On Behalf Of Peter Bowen via Public
Sent: Wednesday, May 10, 2017 1:09 PM
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Cc: Peter Bowen <pzb at amzn.com<mailto:pzb at amzn.com>>
Subject: Re: [cabfpub] Profiling OCSP & CRLs

Ryan,

This seems reasonable when you are dealing with an online CA. When you are dealing with a root CA, it is currently reasonable to only bring it online once a year to update the CRL, as that is the required frequency.  For many offline CAs it is quite a production to use the HSM, so I think the maximum duration of delegated responder certificates signed by root CAs should be at least a year.

Thanks,

Peter

   On May 8, 2017, at 4:51 PM, Ryan Sleevi via Public <public at cabforum.org<mailto:public at cabforum.org>> wrote:

   I think 30 days is what we should target as the upper-bound, so would that be suggesting that we should target 15 days as a SHOULD with 30 as a MUST?

   Or were you suggesting 30 as a SHOULD, 45 as a MUST, which in practice means... well, 45? :)

   On Thu, Apr 27, 2017 at 12:57 PM, Curt Spann <cspann at apple.com<mailto:cspann at apple.com>> wrote:

      Hi Ryan,

      Regarding delegated OCSP responder certificate validity, if 30 days is a desired goal (or a similar timeframe), I would recommend 45 days to allow the renewal to occur every 30 days, with a 15 day buffer for operational issues. Basically, for whatever target validity period we should add some buffer time.

      Cheers,

      Curt

         On Apr 25, 2017, at 4:53 PM, Ryan Sleevi via Public <public at cabforum.org<mailto:public at cabforum.org>> wrote:

         Hi folks,

         In response to various investigations about OCSP performance, operation, and trying to figure out how we can move to a world of more ubiquitous OCSP stapling, one of the things that comes up is that OCSP responses are very much like the pre-BR wild-west of certificates.

         I've tried to capture a starting point for discussion at https://github.com/sleevi/cabforum-docs/pull/2/files?diff=split<https://scanmail.trustwave.com/?c=4062&d=hv-T2ehmPgHfPw10yT5w5XfsN1lhtpSp1lY6OosA_A&s=5&u=https%3a%2f%2fgithub%2ecom%2fsleevi%2fcabforum-docs%2fpull%2f2%2ffiles%3fdiff%3dsplit> . I've tried to annotate the changes, and the reason for the changes, so that people can understand them, their goals, and the implications.

         While I'd like to get this to the point of a Ballot, it's not quite there yet. In particular, it doesn't state Effective Dates, because I want to get a sense of the challenges that each bit may pose :)

         If people find this approach useful, I'd like to also reform the CRL profile in a similar fashion.

         There's also a lot of ways to express these requirements. I considered using a table approach, which I suspect some of our ETSI-audited CA members will be familiar with, and which I find useful, but I thought it best to keep the initial discussions simple and textual, and then we can make it pretty once we're happy with the substance.

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