Subject: [dane] "First" request TLSA records?

From: John Gilmore <[email-masked]>
Date: Thu, 16 Feb 2012 01:13:41 -0800

Section 5 says:

   An application that complies with this document first requests TLSA
   records in order to make certificate associations.

I don't see why an application must "first" request TLSA records.

Is there any problem with applications that "first" open a TCP
connection to the destination TLS server, and "second" request
TLSA records?

Talking to the server will require at least two or three round-trips,
for the TCP 3-phase open, plus the TLS client's initial transmission,
plus the TLS server's response, before any of the TLSA records are
actually needed by the TLS client.  While this is happening, a UDP DNS
request for a TLSA record could frequently return the record,
incurring no additional delay.

This section already says that if TLSA processing fails, the TLS
connection should be "not started or, if the TLS negotiation is
already in progress, MUST cause the connection to be aborted", so it
clearly anticipates this ordering.

Also, it is presumably OK to cache DNS RRsets and reuse them
throughout the TTL (without making a second DNS query for them),
yet this specifies that the application "requests" the records
in order to comply.

I recommend removing the word "first", and also clarifying that
it's talking about making DNS requests, not some other kind of
requests:

   An implementation of this protocol makes a DNS query for TLSA
   records (or uses already-retrieved TLSA records, cached within
   their time to live value), validates these records using DNSSEC,
   and uses the resulting TLSA records and validation status to modify
   its responses to the TLS server.

I also think there's a problem with the name of section 5: "Use of TLS
Certificate Associations in TLS".  I think it was meant to say "Use of
TLSA Certificate Associations in TLS".  But I think it would be
clearer to say "Use of TLSA Records in TLS".  As explained in an
earlier comment, I found the concept of "certificate associations" to
be an unnecessary complication in the description.

(There's a second mention of "TLS certificate associations" in
the first graf under the name, which I think was meant to refer
to "TLSA certificate associations" since the cited section 2.1 
is about the TLSA RDATA, not about TLS.)

	John

---

From: Paul Hoffman <[email-masked]>
Date: Thu, 16 Feb 2012 12:55:52 -0800

>   its responses to the TLS server.

Works for me. Does anyone have any objections to this?

> TLSA Certificate Associations in TLS".  

Yipes! Yes.

> But I think it would be

Your proposed new section title is better even if we leave "certificate associations" in the document because using the records might lead to no certificate associations.

> is about the TLSA RDATA, not about TLS.)

Got it.

--Paul Hoffman