Re: mod_ssl and critical extensions

[Ben Laurie <be...@algroup.co.uk>]

Stephane Bailliez wrote:
> Hi,
> 
> 
> I'm facing an annoying issue during a PKI deployment and integration 
> within an organization.
> 
> The CA is created with the authority key identifier set as a critical 
> extension.
> 
> OpenSSL (including 0.9.7g) chokes (voluntarily) on critical extensions 
> and as a default issue an error such as "Certificate Verification: Error 
> (34): unhandled critical extension"
> 
> The piece of code involved is in 
> crypto/x509/x509_vfy.c::check_chain_purpose
> 
>         if (!(ctx->flags & X509_V_FLAG_IGNORE_CRITICAL)
>             && (x->ex_flags & EXFLAG_CRITICAL))
>             {
>             ctx->error = X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION;
>             ctx->error_depth = i;
>             ctx->current_cert = x;
>             ok=cb(0,ctx);
>             if (!ok) goto end;
>             }
> 
> There is the flag X509_V_FLAG_IGNORE_CRITICAL which can be set when 
> creating the SSL context, unfortunately, mod_ssl does not support any 
> options related to context flags in its configuration, thus it of course 
> fails during authentication with the message above.
> 
> Is there any interest in adding SSL context options to mod_ssl, and if 
> yes, what is the recommended way if it has been thought ?

Its a pretty dumb idea to ignore critical extensions, so I don't think 
this sounds like a great idea...

-- 
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Re: mod_ssl and critical extensions

[Stephane Bailliez <sb...@apache.org>]

Hi Ben,

Thanks for your reply. Comments follow:

Ben Laurie wrote:
>> The CA is created with the authority key identifier set as a critical 
>> extension.
>>
>> OpenSSL (including 0.9.7g) chokes (voluntarily) on critical extensions 
>> and as a default issue an error such as "Certificate Verification: 
>> Error (34): unhandled critical extension"
[...]
>> There is the flag X509_V_FLAG_IGNORE_CRITICAL which can be set when 
>> creating the SSL context, unfortunately, mod_ssl does not support any 
>> options related to context flags in its configuration, thus it of 
>> course fails during authentication with the message above.
>>
>> Is there any interest in adding SSL context options to mod_ssl, and if 
>> yes, what is the recommended way if it has been thought ?
> 
> 
> Its a pretty dumb idea to ignore critical extensions, so I don't think 
> this sounds like a great idea...

I have been reading RFC 3280 says in section 4.2:

    Each extension in a
    certificate is designated as either critical or non-critical.  A
    certificate using system MUST reject the certificate if it encounters
    a critical extension it does not recognize; however, a non-critical
    extension MAY be ignored if it is not recognized.  The following
    sections present recommended extensions used within Internet

    certificates and standard locations for information.  Communities may
    elect to use additional extensions; however, caution ought to be
    exercised in adopting any critical extensions in certificates which
    might prevent use in a general context.



About my case, RFC 3280 make it clear that the authority key identifier 
must not be marked critical (4.2.1.1), so this is one is solved anyway.


Cheers,

Stephane