Re: [pkix] [Technical Errata Reported] RFC5280 (5802) (Martin Rex) Tue, 06 August 2019 21:21 UTC

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To: Russ Housley <>
Date: Tue, 6 Aug 2019 23:21:46 +0200 (CEST)
CC:, "Roman D. Danyliw" <>, IETF PKIX <>, Ben Kaduk <>
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From: (Martin Rex)
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Subject: Re: [pkix] [Technical Errata Reported] RFC5280 (5802)
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Russ Housley <> wrote:
> At the time that these values were assigned, TLS was primarily a
> protocol for WWW security.  It has since been used in may other
> environments.  I do not see how a change to the comment in the
> ASN.1 definition will make any real difference, but I do not really
> have an objection.
> I suggest that this be marked as "Hold for Document Update"

The applicable **STANDARDS** in this area would be
rfc5246 (TLSv1.2) and rfc2818 (HTTP over TLS), and both are
**SILENT** on EKU.

What openssl does is a non-standard, implementation-defined behaviour,
and I consider it a particularly bad idea trying to rewrite history
by filing this as an errata !

I've also seen a public CA (Entrust) issue a TLS server certificate
which asserted id-kp-serverAuth, but was lacking id-kp-clientAuth.
I consider such a certificate a stupid clerical error by Entrust.

Whether TLS client software is willing to use such a certificate
as TLS client certificate, and whether TLS server software is willing
to accept such a TLS server certificate as TLS client certificate
turns out to be *VERY* implementation-specific.

If changing the limited-applicability comment in rfc5280 for
id-kp-serverAuth and id-kp-clientAuth at all, then it should also
include which **application**standards**, if any, gives any meaning
to these EKUs, and where application standards have *NOT* been
giving any meaning all the time, the behaviour is implementation-defined
at best.