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Re: Canonical XML revision

From: John Boyer <boyerj@ca.ibm.com>
Date: Tue, 3 Jan 2006 11:04:26 -0800
To: Joseph Reagle <reagle@mit.edu>
Cc: jose.kahan@w3.org, w3c-ietf-xmldsig@w3.org
Message-ID: <OF704A9180.8C081185-ON882570EB.00637D9A-882570EB.0068CAA0@ca.ibm.com>
Hi Joseph,

>> ... volatility of namespaces.
> I have to agree with John on this point. Yet, unfortunately, this is the 
world that we live in...

It's certainly seeming that way, so I'm glad you agree.
My feeling that c14n should be changed via an erratum amounts to 
recognition that this is the way things are going to be,
so we should align the spec with the world.

> we have had to make compromises, even issue erratum for mistakes, but 
when 
> a change is purposeful and explicit like this (rather than a mistake or
> oversight on our part), I would argue for a new algorithm. John, granted
> that it is a messy world, what is the argument against the new algorithm
?

Well, the world is messy whether we make a new algorithm or issue an 
erratum on c14n 1.0.  In fact,
I think proposing to do an erratum is really more aligned with saying that 
hey the world is not perfect,
so let's just get on with it and let the existing algorithm do what it was 
intended to do.

As to whether this is a mistake or a purposeful change, the distinction 
seems illusory.  Many have complained
that we have made a mistake and would like some kind of fix.  That we did 
not know or believe it was a mistake
is the same as any other kind of oversight in that we did not know or 
believe it was a mistake ;-)

So, the proposal to simply issue an erratum is based on both process and 
technical factors:

1) Process.  This type of issue is exactly what errata are designed for. 
People have misunderstandings that result
in implementations that don't work correctly, so we issue errata to fix 
the problems with W3C recommendations.  They 
aren't set in stone.  Witness, for example, the many errata related to 
attribute values in the core XML recommendation.

2) Technical.  The intent of c14n 1.0 is to be the default 
canonicalization method for XML 1.0.  Other algorithms 
can exist for special purpose results, but you have to explicitly call on 
them to get the special result, and you do
so with an understanding of a special purpose context.  For example, the 
original motivation for creating e-c14n was 
to handle the special context of putting signed XML into a soap envelope 
without breaking the signature.  Problem
is xml:id is not supposed to be a 'special context'.  A recommendation has 
made it part of the core of XML 1.0.

So, because c14n 1.0 is supposed to be the canonicalization method for XML 
1.0, it is what we use by default
for any nodeset to octet stream conversion required during processing of 
the transform sequence.  Such a 
transition is as easy to create as making a same document URI reference 
with *no* expressed transforms.
Even in this case, it is possible to cause problems for inheritance of 
xml:id (e.g. if the referenced element
contained an attribute assigned the type ID by a DTD).  This may sound 
like a bit of an edge case, but with
compound document formats it can actually happen more easily than one 
might at first think.

Hence, the author of a signature element that uses any document subsetting 
would have to also remember to 
fix our bug by manually invoking a new c14n in order to be sure the 
signature will work when applied to documents
that use xml:id-- everywhere in a transform sequence that a nodeset to 
octet stream conversion occurs.
Unless we also issue DSig 1.1 to use C14N 1.1 by default.  That's when 
accepting the messy world and issuing
the erratum starts to look really good. :-)

Best regards,
John M. Boyer, Ph.D.
Senior Product Architect/Research Scientist
Workplace, Portal and Collaboration Software
IBM Victoria Software Lab
E-Mail: boyerj@ca.ibm.com  http://www.ibm.com/software/





Joseph Reagle <reagle@mit.edu> 
12/17/2005 05:47 AM

To
John Boyer/CanWest/IBM@IBMCA
cc
jose.kahan@w3.org, w3c-ietf-xmldsig@w3.org
Subject
Re: Canonical XML revision






On Thursday 15 December 2005 13:46, John Boyer wrote:
> 3) The W3C community seems to be interested in less rigor, not more.
> The thing that's really busted, IMO, is the volatility of namespaces, 

I have to agree with John on this point. Yet, unfortunately, this is the 
world that we live in and unless we can convince the world not to be 
changing the meaning of documents after the fact, we will continue living 
in. (XML is guilty, but for that matter, so is Unicode!) However, since 
our 
concern is security, I would hope we not contribute to the trend. Granted, 

we have had to make compromises, even issue erratum for mistakes, but when 

a change is purposeful and explicit like this (rather than a mistake or 
oversight on our part), I would argue for a new algorithm. John, granted 
that it is a messy world, what is the argument against the new algorithm?
Received on Tuesday, 3 January 2006 19:04:57 UTC

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