[cabfpub] Definition of an SSL certificate

[Ryan Hurst]

Jeremy,

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.

Thoughts?

Ryan



On Thu, Dec 19, 2013 at 8:05 AM, Jeremy Rowley
<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.
>
>
>
> Thanks!
>
>
>
> Jeremy
>
>
>
>
>
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