[Standards] XMPP Certificate checking algorithm

Shumon Huque shuque at isc.upenn.edu
Thu Feb 21 21:02:40 UTC 2008

On Thu, Feb 21, 2008 at 12:58:03PM -0800, Justin Karneges wrote:
> On Thursday 21 February 2008 9:49 am, Peter Saint-Andre wrote:
> > First let's take Shumon's example of upenn.edu, which resolves via SRV
> > to jabber.upenn.edu. In this case, the certificate would include an
> > SRVName of _xmpp.jabber.upenn.edu, which would help the connecting
> > client (or server) to know that jabber.upenn.edu is the authorized
> > domain for connecting to the canonical XMPP service at upenn.edu (e.g.,
> > thus knowing that the DNS SRV lookup did not return poisoned results).
> This is not my understanding.
> If I resolve SRV for _xmpp-client._tcp.upenn.edu and receive 
> jabber.attacker.com as a result, and then I connect to jabber.attacker.com 
> and receive a certificate containing SRVName of 
> _xmpp-client.jabber.attacker.com, then I don't see the security improvement.

No, you'd be expecting to see SRVName of _xmpp-client.upenn.edu.

Presumably the operator of jabber.attacker.com would not be able
to persuade a reputable CA to issue him a certificate with
_xmpp-client.upenn.edu populated in the SRVName field.


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