Subject: ExtendedKeyUsage for TLS Client Authentication

From: Johannes Merkle <[email-masked]>
Date: Tue, 20 Sep 2005 17:56:51 +0200

Hi,
RFC 3280 defines the ExtendedKeyUsage clienthAuth for TLS client
authentication. However, it is not specified whether this
extendedKeyUsage is mandatory for TLS client certificates.

Do clients and servers commonly require this extendedKeyUsage for
TLS client certificates or can it be omitted?

regards,
Johannes

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From: [email-masked] (Peter Gutmann)
Date: Wed, 21 Sep 2005 18:21:23 +1200

>TLS client certificates or can it be omitted?

I've seen it appear in one or two certs from boutique CAs, but I'm not aware 
of anything that cares about it.  It's hard enough finding software that'll 
pay any attention to keyUsage values, let alone extKeyUsage.

In other words you can include or omit it as it suits you.

Peter.

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From: Sam Roberts <[email-masked]>
Date: Wed, 21 Sep 2005 10:50:14 -0400

> >TLS client certificates or can it be omitted?

The SSL/TLS specs (maybe 1.1 is different) say almost nothing about cert
val, they just say "X.509 cert" and reference PKIX, essentially. I guess
you could use an X.509 attribute cert, technically.

The PKIX specs don't specify SHOULDs or MUSTs for particular protocols,
thats up to the protocol group. Though they define an OID to be used for
that protocol I'm not aware of any RFC saying what to use it for. Last
time I looked for more information on this, I found it a bit murky, in
my opinion. Murk is a problem.

Cheers,
Sam

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