Subject: tsv-dir review of draft-ietf-xcon-bfcp-connection-04

From: [email-masked]
Date: Fri, 23 Mar 2007 20:49:45 -0400

I've reviewed this document as part of the transport area
directorate's ongoing effort to review key IETF documents.
These comments were written primarily for the transport
area directors, but are copied to the document's authors
for their information and to allow them to address any
issues raised.

This is a relatively straightforward draft about how a
client opens a TCP connection to a BFCP server when it
has the server's transport address information.

Section 3 ventures into the area of IP address selection -
it references RFC 3484 (which is good) and then goes on to
make additional comments and recommendations on usage and
state of deployment of the techniques specified in RFC 3484.
While there's nothing technically wrong with this text, the
additional comments and recommendations are not specific
to BFCP, and may belong in a more generic document.

Section 4 starts with "All BFCP entities implement TLS ..."
That is correct, as RFC 4582 requires this, but it would be
better to cite RFC 4582 as part of this statement, e.g.,
"[RFC 4582] requires that all BFCP entities implement TLS ..."

In the second paragraph of Section 4, I would change
"can request the use of TLS" to "SHOULD request the use
of TLS".

Section 5.1 specifies that SubjectAltName identities in
certificates are to be preferred to Subject identities.
Is this specific to BFCP or more general?

The following text appears to be an oversight:

   If the client knows the server's IP address, the iPAddress
   subjectAltName must be present in the certificate and must
   exactly match the IP address known to the client.

The client *always* knows the server's IP address (e.g.,
DNS returns it).  I think the intended case here is that
the client contacts the server using the server's IP address
and as a result does not know the server's hostname.  Rephrasing
in that sort of fashion would also express a preference for
hostname as certificate identity, which I believe is desirable.

Section 6 disturbingly shifts between "password" and
"pre-shared key" and appears to get a few things wrong in
the process.  To begin with, the statement that "TLS PSK mode
is subject to offline dictionary attacks." is false when
the PSK is high-entropy.  OTOH, it is correct when the PSK
is low-entropy (e.g., a password, or derived from a password
without introduction of additional entropy).  The discussion
in Section 7.2 of RFC 4279 applies, especially the last
paragraph about PSK generation.  The section needs to be
carefully revised to distinguish between "password" and
"pre-shared key", especially given the mention of use of
PBKDF2 to generate the latter from the former.

Thanks, 
--David
----------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
[email-masked]        Mobile: +1 (978) 394-7754
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