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Re: gnutls fails to use Verisign CA cert without a Basic Constraint

From: Simon Josefsson
Subject: Re: gnutls fails to use Verisign CA cert without a Basic Constraint
Date: Mon, 12 Jan 2009 16:50:09 +0100
User-agent: Gnus/5.110011 (No Gnus v0.11) Emacs/23.0.60 (gnu/linux)

"Douglas E. Engert" <address@hidden> writes:

> Simon Josefsson wrote:
>> "Douglas E. Engert" <address@hidden> writes:
>>> Simon Josefsson wrote:
>>>> The default is to reject V1 CA's, so the application need to supply
>>>> either flag if they want a particular behaviour.
>>>> By default, gnutls_x509_crt_list_verify rejects V1 CAs, but it takes a
>>>> flags parameter.  If you call the verification through
>>>> gnutls_session_verify_peers, you can use the
>>>> gnutls_certificate_set_verify_flags function to set the flags to use
>>>> (like cli.c does).
>>> That will be a problem, as the application is ldap used by nss-ldap.
>>> I have not looked at how they call gnutls, but we don't want to have to
>>> changes these too.
>>> One could argue the application already provides the list of CA certs
>>> it is willing to trust, so why does it need to provide an additional flag?
>> I believe it would break ABI/API compatibility to change this now --
>> applications assume that V1 CA are rejected since that has been the
>> documented behaviour for several years.
>> It seems like a bug in the ldap/nss-ldap code that it doesn't pass the
>> V1 flag if it really wants GnuTLS to permit V1 CA's.
> Its not the application that wants it. As far as I can tell previous
> versions of ldap using OpenLDAP do not have the problem, and only
> after Ubuntu back ported the December fixes did this problem start
> occuring.

The December fixes solved a security problem where some CA certificates
were simply ignored by the validation code, so maybe it only worked by
accident before.

> I understand that you don't want to change your code.

I don't see anything wrong with the code -- with the patch installed on
gnutls 2.6.x, it should behave as per the documentation.

>> For things that aren't documented, I think we can be pragmatic and come
>> up with quick fixes and apply them to the v2.6.x branch as needed.  But
>> anything that changes documented and intended behaviour is not
>> appropriate for our stable branch IMHO.
>>> If the code change on you TODO list to stop when an intermediate CA cert
>>> is found on the trusted CA list, then this would solve my problem,
>>> as the intermediate cert is V3 and has CA:TRUE, and is trusted.
>> Yup.  Fixing that would be neat, and could go onto the v2.7.x branch
>> which we could release as the next stable branch relatively quickly.
> Actually I wrote a mod on this Friday, to do this. I need to clean it
> up today and send it in for your review.
> The CA in question is a Verisign cert used to sign an intermediate cert:
> So trusting this intermediate V3 cert would work for us.

Thanks!  Several people have asked about this feature, solving it would
be useful.

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