Subject: [Dime] Issue39: What to verify in TLS certificates

From: "Asveren, Tolga" <[email-masked]>
Date: Sun, 15 Apr 2007 13:47:19 -0400

If we use subjectAltName for a postcheck for TLS certificates in the following way:
a) dNSName contains the name of the domain, the host claims to be in (OriginRealm in CER/CEA)
b) otherName contains the Id of the application, which the host claims to host for the realm specified in a)

Do we need to verify that the TLS certificate is valid for the domain of the server which was returned by the DNS query as well? It doesn't seem necessary to me, afterall what we care is that the host is valid to provide a given service for a given domain.

As an example if we are interested in getting serviceA for domainA and if at the end of DNS queries we end up with host5.thirdpartydiamnetwork.com, are we really interested that we have a valid certificate for the domain thirdpartydiamnetwork.com?

Currently, in RFC3588 we have the following:

If the server is using a site certificate, the domain name in the query and the domain name in the replacement field MUST both be valid based on the site certificate handed out by the server in the TLS or IKE exchange. 

Does that text refer to the type of usage I think as unnecessary?

   Thanks,
   Tolga 

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From: Victor Fajardo <[email-masked]>
Date: Mon, 16 Apr 2007 11:12:36 -0400

Hi Tolga,

> Do we need to verify that the TLS certificate is valid for the domain of the server which was returned by the DNS query as well? It doesn't seem necessary to me, afterall what we care is that the h…

My personal preference is not to even deal with this issue in the base 
protocol simply because certificate ownership/usage validation is may 
not be limited to diameter only. The "issue" may also be relevant to 
other protocols so its probably better to "specify" the solution (if 
there isn't already one) in more relevant security related documents 
which the base protocol can simply refer to.

> If the server is using a site certificate, the domain name in the query and the domain name in the replacement field MUST both be valid based on the site certificate handed out by the server in the…

The example you mentioned above re-enforces my idea so I agree that it 
maybe better to remove these text from the base spec. It also helps 
simplify the base protocol similar to the removal of the IPsec usage.

regards,
victor

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From: "Asveren, Tolga" <[email-masked]>
Date: Mon, 16 Apr 2007 11:48:33 -0400

Hi Victor,

I think we need to agree on some form of post check for TLS certificates
for interoperability purposes. AFAICS, there is nothing we need to
define new from technology perspective; we just need to decide the
fields to use in the certificate and the meaning of the corresponding
values. Overall, this probably will be a few paragraphs.

I don't know what is the best place to define this, just thinking a
separate document only for this issue could be an overkill (I don't know
whether there are plans for a security type of document).

    Thanks,
    Tolga

-----Original Message-----
From: Victor Fajardo [mailto:[email-masked]] 
Sent: Monday, April 16, 2007 11:13 AM
To: Asveren, Tolga
Cc: [email-masked]
Subject: Re: [Dime] Issue39: What to verify in TLS certificates

Hi Tolga,

Comments inline:

> Do we need to verify that the TLS certificate is valid for the domain
of the server which was returned by the DNS query as well? It doesn't
seem necessary to me, afterall what we care is that the host is valid to
provide a given service for a given domain.

> As an example if we are interested in getting serviceA for domainA and
if at the end of DNS queries we end up with
host5.thirdpartydiamnetwork.com, are we really interested that we have a
valid certificate for the domain thirdpartydiamnetwork.com?
> If the server is using a site certificate, the domain name in the
query and the domain name in the replacement field MUST both be valid
based on the site certificate handed out by the server in the TLS or IKE
exchange. 

regards,
victor

---

From: "Asveren, Tolga" <[email-masked]>
Date: Wed, 18 Apr 2007 09:17:02 -0400

I saw that this issue has been discussed as well in the last IETF
meeting. I agree that a "write once use everywhere" approach makes
sense. One warning though: For Diameter we probably need to verify more
than just domain names (unlike SIP for example). We probably want to
verify domain name+appId pairs. So, I don't know how this could be
addressed in a generic document.

   Thanks,
   Tolga
> From: Asveren, Tolga
> Sent: Monday, April 16, 2007 11:49 AM
> To: [email-masked]
> Subject: RE: [Dime] Issue39: What to verify in TLS certificates
> 
> 
> Hi Victor,
> 
> > b) otherName contains the Id of the application, which the host
claims
> to host for the realm specified in a)
> >