[cabfpub] (Eventually) requiring id-kpServerAuth for all certs in the chain?

Jeremy.Rowley jeremy.rowley at digicert.com
Thu Nov 13 20:59:01 UTC 2014

I realize it's not normative and it's not really a concern for us - more 
of an observation that requiring an EKU in intermediates is opposite of 
the text in the RFC.  The issue is not that we'd break those other 
groups but that we'd force their intermediates to comply with the BRs, 
which might not be possible for some groups.


On 11/13/2014 1:45 PM, Ryan Sleevi wrote:
> Jeremy,
> that language is hardly normative, nor are there normative 
> restrictions on it, nor would it adversely affect the algorithm of RFC 
> 5280 Section 6 (and indeed, if someone was enforcing that CAs not have 
> the EKU, they'd be violating Section 6.1 para3)
>     While the algorithm could be extended to include checks for
>     conformance to the profiles in Sections 4 and 5, this profile
>     RECOMMENDS against including such checks.
> So I'm not sure I fully understand your concern.
> On Thu, Nov 13, 2014 at 12:40 PM, Jeremy.Rowley 
> <jeremy.rowley at digicert.com <mailto:jeremy.rowley at digicert.com>> wrote:
>     Doesn't all this ignore 5280's recommendation that "In general,
>     this extension will appear only in end entity certificates"?
>     Ignoring this might put browsers at odds with other industry
>     groups also using PKI.
>     On 11/5/2014 2:31 PM, Brian Smith wrote:
>>     Gerv,
>>     Please note that Ryan and I appear to be suggesting exactly the
>>     same thing. And, note that what I'm suggesting here is exactly
>>     the same argument I made for interpreting EKU in end-entity
>>     certificates earlier this year or last year: a lack of EKU is
>>     equivalent to "anyExtendedKeyUsage". This is what all (AFAICT)
>>     certificate verification code does today.
>>     Gervase Markham <gerv at mozilla.org <mailto:gerv at mozilla.org>> wrote:
>>         > However, I'm assuming that for the CAs for which the BRs
>>         apply, it is
>>         > already the case that all or most of their intermediates
>>         conform to the
>>         > BRs.
>>         I would hope so. But is it programmatically detectable that
>>         they do? If
>>         so, how? "Publicly audited" is not a determinable
>>         characteristic of an
>>         intermediate.
>>     Your proposal has the same issue. In both proposals, just by
>>     looking at the certificate chain, you can tell whether the
>>     intermediate is required to conform to the BRs or not. The only
>>     difference is that the way Ryan and I are suggesting already
>>     matches what Chrome (on Windows, at lesat), IE, and Firefox are
>>     already doing, whereas you are proposing that all browsers
>>     eventually (5-10 years from now?) be changed to do something new,
>>     without any protection for users until then.
>>         Also, your proposal 1) requires a re-issue of intermediates
>>         for all
>>         private PKIs, right? Because they all need to have EKUs in them?
>>     If a CA certificate chains to a root for which the BRs apply, and
>>     that sub-CA doesn't want to be held to the BRs (ostensibly
>>     because they don't intend to issue SSL certificates), then they
>>     would need to have their sub-CA cert re-issued (and the old one
>>     revoked) with an EKU extension that does not include
>>     id-kp-serverAuth or anyExtendedKeyUsage, unless their certificate
>>     already has such an EKU. That is the only situation in which
>>     re-issuance would be necessary.
>>     If private CAs don't issue SSL certificates, then it would be a
>>     good idea to replace their CA certificates with ones that contain
>>     an EKU that doesn't have id-kp-serverAuth or anyExtendedKeyUsage,
>>     to follow the principle of least privilege. But, they wouldn't be
>>     required to make any change, because the BRs don't apply to them,
>>     assuming that they don't chain to a trusted root. If they do
>>     chain to a trusted root then they're not private and the above
>>     paragraph applies.
>>     Cheers,
>>     Brian
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