[cabfpub] Definition of an SSL certificate

Stephen Davidson S.Davidson at quovadisglobal.com
Fri Dec 20 22:24:01 UTC 2013

Note that there is cross over between this topic and the Certificate Transparency.

As currently discussed, CT will only apply to EV.

However, if it is to expand to all BR-compliant SSL, we need to be able to define better which certificates must be logged in CT.

Best, Stephen

From: public-bounces at cabforum.org [mailto:public-bounces at cabforum.org] On Behalf Of Ryan Hurst
Sent: Friday, December 20, 2013 6:08 PM
To: Jeremy Rowley
Subject: Re: [cabfpub] Definition of an SSL certificate

One issue with my proposal is that while it is true browsers can update themselves fairly well (in about 3y you have 80% ubiquity of a change) this is not true of all of the other SSL clients that are at risk of the practices of CAs who do not follow the current assumptions of deployed clients.

And even in the case of browsers you are exposed to risks of this bad issuance practice for the duration of the deployment window.

Issuance practices and who is trusted however can change much quicker (excluding bureaucracy) and could stop the issue in its track.

Ryan Hurst

Chief Technology Officer

GMO Globalsign

twitter: @rmhrisk

email: ryan.hurst at globalsign.com<mailto:ryan.hurst at globalsign.com>

Sent from my phone, please forgive the brevity.

On Dec 20, 2013, at 1:38 PM, "Jeremy Rowley" <jeremy.rowley at digicert.com<mailto:jeremy.rowley at digicert.com>> wrote:

   That is the goal since intent is irrelevant once an attacker has a certificate.

   I agree with your OID approach. Requiring BR DV/OV/IV/EV OIDs to enable server authentication is really the fastest way to scope the BRs and determine whether a certificate needs to comply.  All other solutions require a lot coordination with government bodies, meaning we won’t see any real change for several years.  I highly doubt the entire EU community will move away from using anyEKU over the next 5 years.

   From: Ryan Hurst [mailto:ryan.hurst at globalsign.com]
   Sent: Friday, December 20, 2013 1:17 PM
   To: Jeremy Rowley
   Cc: CABFPub
   Subject: Re: [cabfpub] Definition of an SSL certificate


   The proposal seems to be to re-write the definition to represent the intent of the issuer (I only expected this to ever be used in this way) vs what the technical capability of the certificate that they have issued.

   In my opinion the problem with this approach is that whats material is not what the intent of the action was but what the result of it is. Basically any certificate that is technically capable of being used as a publicly trusted SSL certificate IS a publicly trusted SSL certificate even if that was not the intent.

   If the group decides to go this way I think that browsers should change what they require of SSL certificates so that only those that match this intent can be technically used.

   This of course is quite difficult since the group has refused to mandate certificate policies map to the common CABF OIDs for the corresponding policies but  not addressing this seems to expose the internet to risk.



   On Thu, Dec 19, 2013 at 8:05 AM, Jeremy Rowley <jeremy.rowley at digicert.com<mailto:jeremy.rowley at digicert.com>> wrote:

   We are looking to clarify the scope of the BRs.  Right now the BR scope is very loose and subjective: “This version of the Requirements only addresses Certificates intended to be used for authenticating servers  accessible through the Internet.”

   This loose definition excludes internal names (which are not typically accessible through the Internet), a type of certificate the BRs are clearly designed to regulate (see 11.1.4).  In addition, a CA could easily issue a certificate outside of the BRs  that could later be used in a TLS/SSL attack simply because the certificate wasn’t intended to be used for SSL.

   Issuance of certificates outside the BRs may not be intentional, especially by CAs who aren’t regularly issuing SSL certificates.  These CAs may not be aware that the BRs apply to their certificates and may not realize their client certificates could be used for SSL since “authenticating servers” is not a well-defined term.

   Clarifying the scope will ensure that every CA is aware of the minimum standards and what they cover.  Originally, the idea was to tie the scope to the values in the EKU.  Unfortunately, there are several obstacles to this approach:

   1)      Grid Certificates require serverAuth in the EKU.  It’s unclear whether these certs should be covered.

   2)      Per 5280, browsers treat the absence of an EKU and the anyEKU as serverAuth, meaning they are enabled for TLS Server Authentication.

   3)      The FBCA requires anyEKU in several certificates.  These are clearly client certificates and are outside the BR scope.

   4)      Qualified certificates in the EU have either the anyEKU present or omit the EKU.  They are client certs and clearly not covered by the BRs.  However, they can be used  for server authentication.

   For qualified certificates, Moudrick provided the following guidance:

   “Certificates using applications MAY require that the extended key usage extension be present and that a particular purpose be indicated in order for the certificate to be acceptable to that application.

   If a CA includes extended key usages to satisfy such applications, but does not wish to restrict usages of the key, the CA can include the special KeyPurposeId anyExtendedKeyUsage ***in addition to the particular key purposes required by the applications***.

   So a QC pretending to be RFC 5280/BR and ETSI (web server QCs) compliant would have to at least have:

   QC + [anyEKU] + id-kp-serverAuth + {DV/OV/EV}

   I'm quite confident that the absolute majority of QCs issued so far (that have anyEKU, see Mark Janssen's 08/08/2013 - thank you Stephen) do not contain any DV/OV/EV policy IDs, so why not accept them as BR compliant but not sufficient for TSL/SSL establishment?

   In order for a QC to have a TSL/SSL capability, BR may require:

   QC + {{id-kp-serverAuth and/or id-kp-clientAuth} + {DV/OV/EV}} (optionally no anyKEY allowed).

   A practical interpretation: a WEB server that also does some web site related document/content signing.”

   There appears to be a significant conflict between the CAB Forum’s work and the standards set by other bodies.  In particular, their use of the anyEKU or omission of an EKU is permitting the realm of client certs to overlap SSL certs.  Approaching each government body to stop this practice is not feasible and will take a very long time to complete

   Hopefully this summary helps inspire ideas on where we can go from here.  I’m looking forward to ideas.



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