RE: Absent keyUsage in certificates

["David Cross" <dcross@xxxxxxxxxxxxx>]

I agree for CA certificates, the Key Usage extension MUST be asserted.
However, in client (end entity) certificates, this is extremely
disadvantageous as it makes deployments and future application
consumption difficult.  In fact, many many companies and oragnizations
have demanded the acceptance and usage by applications EE certs with
this extension absent to indicate all purposes. 


David B. Cross 


-----Original Message-----
From: owner-ietf-pkix@xxxxxxxxxxxx [mailto:owner-ietf-pkix@xxxxxxxxxxxx]
On Behalf Of Sam Roberts
Sent: Monday, May 30, 2005 7:25 AM
To: ietf-pkix@xxxxxxx
Subject: Re: Absent keyUsage in certificates


Wrote Peter Gutmann <pgut001@xxxxxxxxxxxxxxxxx>, on Mon, May 30, 2005 at
09:04:15PM +1200:
> If anyone from Verisign-called-Thawte is reading this, could you 
> please fix your certs to include the keyUsage extension?  They're 
> currently being issued without any keyUsage indication (or at least 
> some of them are), which is causing some debate about how to apply 
> them (the contact details I have for someone at Verisign seem to be
out of date).
> 
> Also, could the current wording around keyUsage in bride-of-3280 be 
> improved to indicate what the correct usage is if the extension is 
> absent?  Squinting at the text sideways, it currently says that the 
> key can be used for anything
> *except* cert and CRL verification, a rather strange 
> allow-some/deny-some interpretation when it's more normal to have a 
> default of either allow-all or deny-all (fail-open/fail-closed) in the

> absence of any further instructions,

I agree that allow-all or deny-all is sensible, and special-casing two
of the bits would be weird, but isn't allow-all what is specified now?

This interpretation is based on the validation rules, section 6.1.4,
rule (n):

  If a key usage extension is present, verify that the keyCertSign bit
  is set.

I can't see anything that says that absence of Key Usage should trigger
chain validation failure.  Its a long RFC, an you point to the text you
are "squinting sideways" at?

> but this is quite hard to see for anyone who doesn't already know in 
> advance how keyUsage works.  The sentence "Conforming CAs MUST include

> this extension in certificates that contain public keys that are used 
> to validate digital signatures on other public key certificates or
CRLs" is particularly obtuse.
> 
> I would suggest adding either:
> 
>   Conforming CAs MUST include this extension in all certificates.

Why MUST an end-entity cert include a Key Usage, not including it is a
good way of specifying allow-all. You want to forbid allow-all?

Cheers,
Sam

--
http://www.certicom.com