Subject: Re: [TLS] TLS-OBC proposal

From: Martin Rex <[email-masked]>
Date: Tue, 6 Sep 2011 22:04:58 +0200 (MEST)

Chris Richardson wrote:
> 
> Should that be a MUST, or at least a SHOULD?  If OBC has been
> negotiated, why would a CA-signed cert be used?

The original design behind TLS client certs is exactly the idea of per-server
client certs.

Each Service operator would run a CA and issue certificates
to clients, and the TLS client would be able to automatically select
an appropriate client cert based on CA listed in the
certification_authorities list sent by the TLS server.

Btw. in SSLv3 and TLSv1.0 the protocol does _NOT_ allow to send
a Certificate Request handshake message with an empty
certification_authorities element, although there are numerous
defective SSL&TLS server implementations out there that ignore
that protocol requirement, so TLS clients usually do not break
on such broken server behaviour.   Our TLS client will unconditionally
send back an "SSL no certificate alert" (for SSLv3) or and empty
Certificate handshake message (TLSv1.0) when receiving an
invalid CertificateRequest handshake message with an empty
certificate_authorities list.

Some extremely broken TLS server implementations (I've heard complaints
about a big network components vendor) even go as far as completely
lacking a possibility to configure CA certificates for the
certificate_authorities field of the CertificateRequest handshake message,
which essentially means that they do support TLS client certificates
_at_all_ (in a fashion compliant to the  TLS protocol spec).

-Martin