Re: Review of draft-saintandre-tls-server-id-check

[Shumon Huque <[e-mail]>]

On Wed, Sep 08, 2010 at 11:08:29PM +0200, Stefan Santesson wrote:
> 
> On 10-09-08 9:53 PM, "Shumon Huque" <[e-mail]> wrote:
> > The output of the SRV record lookup contains a target hostname,
> > not a service name, so it's not applicable to the SRVName name
> > form. The target could be used in another name form (dNSName)
> > as the reference identifier, but then the client needs to convince
> > itself that the lookup was done securely (DNSSEC or some other
> > means) otherwise there's a security problem.
> 
> I disagree,
> 
> A client can use the output from the DNS lookup also from a normal insecure
> DNS server.
> 
> The only thing the client need to do is to verify that the domain name
> provided in the input to the lookup matches the host names provided in the
> output. It can then safely use the host names in the SRV record as reference
> identifiers IF the SRV-ID in the server certificate matches the the
> reference identifier.

This only works if the certificate matching rules say something 
like "match the SRVName AND also match the DNS resolved target
hostname in dNSName". If a client attempts to match _only_ the DNS 
resolved hostname without DNSSEC, there is a security problem.

The question is: what should the certificate matching rules say
when encountering a certificate with multiple identity types?
Right now the draft approximately says "find a match" (ie. find
ANY match), rather than match some logically AND'ed combination of 
identity types.

  http://tools.ietf.org/html/draft-saintandre-tls-server-id-check-09#section-4

-- 
Shumon Huque
University of Pennsylvania.