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RE: KeyInfo questions/comments

From: Barb Fox <bfox@Exchange.Microsoft.com>
Date: Mon, 13 Mar 2000 15:02:37 -0800
Message-ID: <997DBB511DD1D311A47A00508B6FB330ED3675@df-sparky.platinum.corp.microsoft.com>
To: "'Carl Wallace'" <cwallace@erols.com>, Barb Fox <bfox@Exchange.Microsoft.com>, dsig <w3c-ietf-xmldsig@w3.org>
Cc: pmhesse@cygnacom.com
Hi Carl!
Sorry, but I can't agree that implementing KeyValue is a burden for
developers. It can't be.  If PKIX developers are using AKI-SKI chaining
(which they would have to for any meaningful path discovery), then they
would need to resolve to keys anyway. Unfortunately, MANDATORY can't be
"either - or".  The underlying IETF concept here is to assure base
interoperability, not offer a negotiation opportunity. So, I stand by our
wg's decision for KeyValue as the only semantically neutal option.  
On DSA: I pulled down Santosh's paper and re-read it, and while it may have
been "accepted in the X.509 world", I see no reason that it applies here for
the reason I stated before. Parameter substitution is always an issue which
is why we decided that it takes all of the components (y, g, p, q) for a key
to match a "trusted" verification key.  
-----Original Message-----
From: Carl Wallace [mailto:cwallace@erols.com]
Sent: Monday, March 13, 2000 12:05 PM
To: Barb Fox; dsig
Cc: pmhesse@cygnacom.com
Subject: Re: KeyInfo questions/comments

Yes I am saying KeyValue would be a burden for developers.  Implicit in the
KeyValue requirement is an attempt to bridge trust management methods.  Such
a bridge is not the charter of this group.  If trust management schemes are
not interoperable, so be it.  Forcing KeyValue on a PKI-aware environment as
inappropriate/difficult as forcing X509Data support on a non-PKI environment
environment.  Furthermore, it is quite likely that the methods taken by
different implementers to provide support for KeyValue in specific
environments will introduce their own interoperability issues.  Why not
require implementations that use KeyInfo to implement either KeyValue or
X509Data/X509Certificate?  That seems like a reasonable solution.  
The DSA issue is related to parameter substitution.  The paper at the link I
gave describes it in detail.  The premise of the paper is accepted in the
X.509 world and there seems to be no reason to violate it here.    

----- Original Message ----- 
From: Barb Fox <mailto:bfox@EXCHANGE.MICROSOFT.com>  
To: 'Carl Wallace' <mailto:cwallace@erols.com>  ; Barb Fox
<mailto:bfox@EXCHANGE.MICROSOFT.com>  ; dsig
Sent: Monday, March 13, 2000 2:02 PM
Subject: RE: KeyInfo questions/comments

Hi Carl:
KeyInfo is already optional. Are you saying that implementing KeyValue is a
burden for developers?  We chose KeyValue as mandatory to implement because
it's the only semantically-neutral option. Every other choice indirects the
public key, so this approach should guarantee the greatest range of
For DSA, think of the "key" as including these group parameters. To use a
key for validation of a signature, the recipient would need to have all
components of it (y, g, p, q) match the "key" he trusts.  

-----Original Message-----
From: Carl Wallace [mailto:cwallace@erols.com]
Sent: Monday, March 13, 2000 10:24 AM
To: Barb Fox; dsig
Subject: Re: KeyInfo questions/comments


If the intent is to leave out issues related to trust management then I
suggest my proposal that no KeyInfo element be required is the best
solution. A digital signature specification that chooses to leave out trust
management issues is bound to have interoperability issues in that domain.
Attempting to find a common ground for interoperability without addressing
trust management is a tall order, and I contend that KeyValue only
complicates the issue for implementers. Consider an implementation that is
deployed in a PKI-enabled environment, a likely scenario. Why force it to
deal with KeyValue-related trust issues out-of-band, or otherwise, when such
issues can be dealt with cleanly using some combination of the X509Data
elements? There are plenty of places in the spec where application-specific
content can hinder interoperability, perhaps this should be another one. 

As for DSA parameters, there is no trust management architecture in which
DSA parameters used to validate a signature should be extracted from the
message they will be used to verify. As such, they need never be present in
the message and users can be spared passing around thousands of needless
bits by requiring their absence. 

- Carl

----- Original Message ----- 

From: Barb Fox <mailto:bfox@Exchange.Microsoft.com>  
To: 'Carl Wallace' <mailto:cwallace@erols.com>  ; dsig
Sent: Monday, March 13, 2000 12:24 PM
Subject: RE: KeyInfo questions/comments

In response to your first issue:  Do not assume that because an application
includes a KeyValue as KeyInfo that the recipient does not have some a prior
validation for that key.  Unlike PKIX, we explicitly chose to leave trust
managment mechanisms out of this standard, and we selected KeyValue as the
MUST implement option to assure basic interoperability.  I believe that
presumption of a trust model (as in values passed must be trusted) is also
the basis of your second issue. 
Barbara Fox
-----Original Message-----
From: Carl Wallace [mailto:cwallace@erols.com]
Sent: Monday, March 13, 2000 8:18 AM
To: dsig
Subject: KeyInfo questions/comments

1) Why require support for unprotected, unvalidated keys?  It seems a little
strange to make KeyInfo OPTIONAL to accommodate applications that, for
whatever reason, do not wish to disclose KeyInfo then to mandate that
applications wishing to use some form of KeyInfo provide support for what
may be the weakest option.  Perhaps no KeyInfo option should be required.  

2) DSA support is required.  Where the KeyValue element is used to identify
a DSA key the presence of parameters is required (see section 6.4.1).  The
DSA parameter problem present in X.509 described by Santosh Chokhani (see
<http://www.cygnacom.com/downloads/dsaflaw.zip> ) is also a problem here.
Parameters found in KeyValue cannot be trusted, should not be used and thus
need not be included.  The requirement that parameters must be included
should be replaced with a requirement that parameters must be absent and be
obtained from a trusted source.

3) Section 4.4 states that "applications may define and use any (KeyInfo)
mechanism they choose through inclusion of elements from a different
namespace."  This doesn't appear to be possible given the current DTD and
schema definitions.
Carl Wallace
CygnaCom Solutions
Received on Monday, 13 March 2000 18:03:55 UTC

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