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RE: AW: Errors and Questions

From: Brian LaMacchia <bal@microsoft.com>
Date: Fri, 28 Jul 2000 13:58:01 -0700
Message-ID: <FB9575840F91DC4EACEB5CD6F573A20D7CEB7E@red-msg-20.redmond.corp.microsoft.com>
To: "'tgindin@us.ibm.com'" <tgindin@us.ibm.com>, Gregor Karlinger <gregor.karlinger@iaik.at>
Cc: Barb Fox <bfox@exchange.microsoft.com>, "Joseph M. Reagle Jr." <reagle@w3.org>, XML <w3c-ietf-xmldsig@w3.org>
The fact that we are continuing to have problems settling on a schema for
X509Data this late in the game causes me to reconsider including X509Data in
the core DSIG specification.  In fact, the more I think about it, the more I
am coming to believe that we should remove X509Data from XMLDSIG and move it
to a parallel, subordinate draft that would be generated by or inconjunction
with the PKIX/X.509 community.  I say this because X509Data is not core to
XMLDSIG and I fear it will hold up progression of the standard.  If other
folks agree we should discuss this in Pittsburgh next week.

Here's my thinking on the matter:

1) Based on our experience so far, it's clear that trying to create an
XML-based representation for X.509/PKIX Part 1 data is a non-trivial task.
The problem Kent raised with RFC 2253 encoding of a DN is one example.  To
quote from his previous mail:

>RFC 2253 has an original method to escape non-ASCII octets.  It
>is strange for XML applications.  An example in RFC 2253,
>	<X509SubjectName>SN=Lu\C4\8Di\C4\87</X509SubjectName>
>is not suitable for XML.  I think XML applications prefer
>following form:
>	<X509SubjectName>SN=Lu&#x10d;i&#x107;</X509SubjectName>

He's absolutely right, RFC2253 isn't XML-friendly.  (How could it be when it
predated XML?)  While we could backpatch 2253 with something like his
proposal, it seems to me that if we're going to define an XML-friendly way
of representing a DN then we really ought to do it following the tenets of
XML.  What I mean is that since a DN is a structured object, its XML
representation should reflect that structure, too.  Using the Subject Name
from Kevin Regan's last S/MIME message to the list as an example, I could
see something like this for X509SubjectName:

<X509SubjectName>
	<E>kevinr@valicert.com</E>
	<CN>Kevin Regan</CN>
	<OU>Digital ID Class 1 - Microsoft Full Service</OU>
	<OU>Persona Not Validated</OU>
	<OU>www.verisign.com/repository/RPA Incorp. by
Ref.,LIAB.LTD(c)98</OU>
	<OU>VeriSign Trust Network</OU>
	<O>VeriSign, Inc.</O>
</X509SubjectName>

(There'd have to be an X.509/PKIX namespace for these elements, of course,
but I've elided that.)  We'd use standard UTF-8 encoding rules for non-ASCII
octets, so Kent's example would become:
	<X509SubjectName><SN>Lu&#x10d;i&#x107;</SN></X509SubjectName>

Obviously, this is just the tip of the iceberg when it comes to X.509/PKIX
Part 1.  There are many portions of that specification, and the related
specifications that could have a lightweight XML-based representation.  (I
don't think, though, that the XML representation should necessarily be
derived from the ASN.1 representation; seems to me a better job could be
done looking at the actual data structures.)

2) X509Data is not core to XMLDSIG.  This is clear from RFC 2807 (the
requirements doc), esp. 2.3.2 and 2.5.  We've said that trust semantics are
specifically outside the standard, and support for X509Data is already
OPTIONAL in XMLDSIG.  The more we dig into X509Data the more complexity we
find.  Some folks want to communicate entire chains fo certs...how should we
represent chains?  It's not as easy as just embedding all the certs, because
you might want to reference published certificates for part of the chain to
keep message size down.  How should complex cross-certification webs be
represented?   Is it even the job of X509Data to communicate ordering
information, or is it just a bag of certs?

3) X509Data and the "everyting in a KeyInfo element relates to a single key"
dictum.  It's clear that we still can't decide what it means for X509Data
that "[m]ultiple declarations within KeyInfo refer to the same key."
Follwing that convention we have chains represented as follows:

<KeyInfo>
  <X509Data><X509Certificate>...cert A data...</X509Certificate></X509Data>
  <X509Data><X509Certificate>...cert B data...</X509Certificate></X509Data>
  <X509Data><X509Certificate>...cert C data...</X509Certificate></X509Data>
  <X509Data><X509Certificate>...cert D data...</X509Certificate></X509Data>
</KeyInfo>

Where A, B, C and D all "relate" to the same key, e.g. part of a chain.
Gregor, I believe you and Tom may have misread/misinterpreted Barb's
previous statement.  "One per clause" means you can have exactly one
X509Certificate element per X509Data.  A chain would be represented as
multiple X509Datas within a single KeyInfo, as in my example.  If this isn't
satisfactory, perhaps the WG needs to revisit the decision from Victoria,
but in any case the continuing confusion/discussion is further evidence that
X509Data isn't ready for prime time.

4) PKI data neutrality.  Finally, it seems weird to me that this working
group is spending so much of its limited resources arguing over one
particular type of trust-related data for keys.  We agreed to give the other
IETF-recognized trust semantics (PGP and SPKI) a slot in the standard where
they could plug in their own sub-elements.  With PGP we went slightly
further and put out a proposed set of PGPData elements, but I have no idea
if that's really going to be sufficient for their needs.  SPKI we've
explicitly said will be defined by the SPKI WG.  Seems to me that we should
deal with X509Data on equal terms.

So, in summary, I propose that we remove the detailed element schema from
sections 4.4.4-4.4.7 (X509Data, PGPData, SPKIData and MgmtData) and spin
thouse sections out to subordinate drafts.  We can reserve the tags
"X509Data", "PGPData", "SPKIData" and "MgmtData" within the XMLDSIG
namespace, and work on a spec for X509Data can happen in parallel with the
finishing up XMLDSIG starting with what we currently have in 4.4.4 as a
strawman.  X509Data is not core to the standard nor many important scenarios
(certainly I have scenarios that don't require X509Data), so this seems the
best way to allow further work on this particular component to happen
without holding up the entire standard.

					--bal


-----Original Message-----
From: tgindin@us.ibm.com [mailto:tgindin@us.ibm.com]
Sent: Friday, July 28, 2000 11:55 AM
To: Gregor Karlinger
Cc: Barb Fox; Joseph M. Reagle Jr.; XML; Brian LaMacchia
Subject: Re: AW: Errors and Questions


     I agree with you.  I don't see why we should shift from having lots of
certificates allowed, with no guaranteed relationship between them, to
having only the EE certificate allowed and not allowing chains.  It makes
more sense, IMO, to set requirements on which certificates are allowed
along the lines of some earlier suggestions - for example, allowing only
one EE certificate and requiring that all other certificates be part of a
certification chain for that one.  We could even require that there be only
one chain and that the certificates appear in leaf-first order - it would
still be better than just a leaf and it would not be very hard to
implement.

          Tom Gindin

"Gregor Karlinger" <gregor.karlinger@iaik.at>@w3.org on 07/27/2000 03:54:06
AM

Sent by:  w3c-ietf-xmldsig-request@w3.org


To:   "Gregor Karlinger" <gregor.karlinger@iaik.at>, "Barb Fox"
      <bfox@Exchange.Microsoft.com>, "Joseph M. Reagle Jr." <reagle@w3.org>
cc:   "XML" <w3c-ietf-xmldsig@w3.org>, "Brian LaMacchia"
      <bal@microsoft.com>
Subject:  AW: Errors and Questions




Sorry, I hit the  wrong key on my keyboard, and the message was gone ...

Hi Barb,



 > [GK20]Only a single certificate possible  here?  [Barb]  Yes. One per
clause.


Please see my comment on [GK20] in my  previous message:

http://lists.w3.org/Archives/Public/w3c-ietf-xmldsig/2000JulSep/0176.html

Regards,  Gregor
---------------------------------------------------------------
Gregor  Karlinger
mailto://gregor.karlinger@iaik.at
http://www.iaik.at
Phone +43 316  873 5541
Institute for Applied Information Processing and  Communications
Austria
---------------------------------------------------------------
Received on Friday, 28 July 2000 16:58:46 GMT

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