On Thu, Sep 24, 2009 at 04:23:03PM +0200, Michael Prinzinger wrote:
> > Are you saying that the accepting system expects X.509 client credentials
> > from the connecting system, but that the payload (encrypted to the
> > receiving node's public key) also contains the same certificate, and
> > you want to check that the peer client matches the encrypted request?
>
> Yes.
>
> > If so, trust chain verification is completely irrelevant here. You
> > don't need to repeat the handshake, rather implement a verification
> > callback that accepts untrusted certificates (X.509 trust anchors seem
> > inapplicable in this context) and compares them (via the public key
> > fingerprint) to the designated certificate in the message payload.
>
> Yes, this would do what I want.
> I would have to call BIO_do_handshake with a customized verification call
> back, that decrypts the payload, reads the certificate and compares them
> to the one offered by the client?
No, your verification callback just always succeeds, allowing invalid
trust chains, expired certificates, ... to be used. After the handshake,
when you receive and decrypt the payload, you compare the enclosed peer
certificate (public key fingerprint) with the peer certificate (public
key fingerprint) from the SSL session.
> Since there are no central trust authorities withtin the context of this
> protocol, I can only directly verify a certificate, resp. some message
> signed with the corresponding private key.
"Verify" is the wrong term here. It suggests X.509 PKI hierarchies and all
that jazz. You just want to validate the peer's client cert against the
message routing data in the payload.
> > If you want something else, you must explain it in a lot more detail.
> >
> > Note, your problem is understanding the crypto protocol design, not
> > OpenSSL. You are using this list to get help with X.509 and cryptography,
> > not really the OpenSSL API, so we are somewhat outside the list charter,
> > but such questions are relatively common here...
>
> Thank you for helping anyways.
> If you know a good resource that explains X.509 infrastructure, I'd be glad
> to read it.
Actively avoid reading anything about X.509 infrastructure. Reading a
decent applied cryptography book + a decent book general about SSL/TLS
would be better (skipping the parts that deal with X.509 "infrastructure").
--
Viktor.
______________________________________________________________________
OpenSSL Project http://www.openssl.org
User Support Mailing List openssl-users@openssl.org
Automated List Manager majord...@openssl.org
