Maxim Dounin mdounin at mdounin.ru
Wed Oct 23 00:25:25 UTC 2013


On Tue, Oct 22, 2013 at 02:31:01PM +0100, Rob Stradling wrote:

> On 22/10/13 13:09, Maxim Dounin wrote:
> >Hello!
> >
> >On Mon, Oct 21, 2013 at 10:40:43PM +0100, Rob Stradling wrote:
> <snip>
> >>The following approach seems to work:
> >>
> >>#if OPENSSL_VERSION_NUMBER >= 0x10002000L
> >>     // OpenSSL 1.0.2 lets us do this properly
> >>     Call SSL_CTX_add1_chain_cert(ssl->ctx, x509)
> >>#else
> >>     If (number of ssl_certificate directives > 1)
> >>         // Put this intermediate in the "trusted certificates store"
> >>         Call X509_STORE_add_cert(ssl->ctx->cert_store, x509)
> >>     Else
> >>         // This is what Nginx does currently
> >>         Call SSL_CTX_add_extra_chain_cert(ssl->ctx, x509)
> >>     End If
> >>#endif
> >
> >An unwanted side effect would be that this will allow client
> >certificate authentication to use certs from a server's
> >certificate chain.  Probably not something we want to happen.
> Yes, that's a potentially unwanted side effect.  But unfortunately,
> AFAICT, putting the intermediates into the "trusted certificates
> store" is the only way to implement this feature with OpenSSL
> <1.0.2.
> Could you live with this side effect if the user had to explicitly
> enable it?  Like this...

I think this should be left up to a user.  That is, if user want 
us to work this way, he can use the ssl_trusted_certificate directive 
to supply needed certs.


> >>(A side effect is that I'm seeing "OCSP_basic_verify:signer
> >>certificate not found" from the stapling code in both cases where I
> >>don't call SSL_CTX_add_extra_chain_cert() - another thing to look
> >>into!)
> >
> >OCSP Stapling code uses certificate chain as available via
> >SSL_CTX_get_extra_chain_certs() to look for issuer cert, see
> >ngx_ssl_stapling_issuer().
> Yep, I'd found that.
> >Though certs from a trusted store should be used too.
> ngx_event_openssl_stapling.c provides OCSP_basic_verify() with 3
> places to look for certs: inside the OCSP Response, the
> extra_chain_certs and the "trusted certificate store".
> OCSP_basic_verify() calls ocsp_find_signer() to locate the
> certificate that signed the OCSP Response, but this function only
> looks in the first 2 of those 3 places.  (There's a comment "/*
> Maybe lookup from store if by subject name */", but no associated
> code).

Err, sorry, I've somehow misread you mail and tought you are 
talking about "issuer certificate not found" errors.  The 
OCSP_basic_verify() indeed will likely require additional fixes 
and/or workarounds.

> This is a problem for OCSP Responses that are signed directly by the
> CA certificate (rather than by a delegated OCSP Response Signing
> Certificate).  It currently works because that CA certificate is
> almost certainly present in extra_chain_certs.  But, to support
> RSA+DSA+ECC certs signed by different intermediates, we already
> established that we can't use extra_chain_certs.
> To workaround this, I think the only option would be to pass to
> OCSP_basic_verify() a different STACK_OF(X509) that includes all of
> the extra_chain_certs plus whatever other CA certificates that Nginx
> can lay its hands on!

Given the number of problems, it might be easier to assume the 
chains must be the same.  How it looks from a CA point of view?

Maxim Dounin

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