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RE: Three Issues for C14N Consideration

From: Richard D. Brown <rdbrown@GlobeSet.com>
Date: Mon, 21 Jun 1999 09:56:43 -0500
To: "'Hiroshi Maruyama'" <MARUYAMA@jp.ibm.com>, <w3c-ietf-xmldsig@w3.org>
Cc: "'Joseph M. Reagle Jr.'" <reagle@w3.org>
Message-ID: <00f501bebbf6$4740a380$0bc0010a@artemis.globeset.com>

> To do context-independent canonicalization, we need to
> consider all the
> namespaces used in a single element (but not a subtree).

Does it mean that every element shall explicitly declare its namespace as
well as the namespaces of its attributes (if different)?

I suppose that, in such circumstances, an element will be always bound to
the default namespace declared on the element and, therefore, will never
contain a namespace prefix. In addition, the element will define the
namespaces ns<x> for each of its attribute that is bound to a namespace
other than the element's namespace. Probably, the rank x for each namespace
prefix will be allocated on a first reference basis after ordering of the

Am I correct?


Richard D. Brown

> example, see
> the "myns:goodbye" element.  This element contains three namespaces
> prefixed by "myns", "yourns", and the default namespace (two
> of them are
> inherited from the surronding context). The canonicalized form
> (context-independent version of JC's C14N) of this document
> is as follows
> (for readability I added extra spaces for indentation).
> <?xml version="1.0" encoding="UTF-8"?>
> <root>
>  <hello xmlns="http://ibm.com/schemaA">
>    <goodbye xmlns="http://ibm.com/schemaB"
>             xmlns:n1="http://ibm.com/schemaA"
>             xmlns:n2="http://ibm.com/schemaC"
>             n1:value="123"
>             n2:value="456">
>       <order xmlns="http://ibm.com/schemaD">
>         <title xmlns="http://ibm.com/schemaD">XML and Java</title>
>         <publisher xmlns="http://ibm.com/schemaD">Addison
> Wesley</publisher>
>         <price xmlns="http://ibm.com/schemaD" unit="USD">39.95</price>
>       </order>
>    </goodbye>
>  </hello>
> </root>
> The "goodbye" element uses the three namespaces, each of
> which is declared
> in the same document.  This is actually more readable than any of the
> hexified versions (either URI or MD5 of URI).  It is not as
> long as the
> hexified versions either if the URIs are not very long.
> --
> Hiroshi Maruyama
> Manager, Network Applications, Tokyo Research Laboratory
> +81-462-73-4576, maruyama@jp.ibm.com
> Also Associate Professor, Dept. of Computer Science, Tokyo
> Institute of
> Technology
> +81-3-5734-3953, maruyama@cs.titech.ac.jp
> From: "Joseph M. Reagle Jr." <reagle@w3.org> on 99/06/18 02:41 AM
> To:   "IETF/W3C XML-DSig WG" <w3c-ietf-xmldsig@w3.org>
> cc:    (bcc: Hiroshi Maruyama/Japan/IBM)
> Subject:  Three Issues for C14N Consideration
> If you have strongly held thoughts on any of these issues,
> let me know (cc
> the list).
> 1. Presently, the C14N of XML includes expanded general entities which
> produces a standalone document. Obviously parameter entities aren't a
> problem, but PIs might be. Do you care about PIs?
> 2. Should the canonical form include an XML declaration with version
> number?
> 3. If C14N fails because of the unavailability of an external
> entity, do
> XML Signature applications want to know?
> *. Next week the Syntax WG will discuss Don and Hiroshi's n1 vs. hash
> prefix
> issue.
> *. Dan Connolly committed to adding a requirement to the XML Schema
> Requirements Document from us and the I18N
> (internationalization) IG that a
> datatype have a normalized/C14N form.
> [1]
> Date: Thu, 17 Jun 1999 09:47:13 -0700
> To: "XML Syntax WG" <w3c-xml-syntax-wg@w3.org>
> From: Tim Bray <tbray@textuality.com>
> Subject: C14n issue N2 - Processing Instructions
> Status:
> Suppose we have PIs in the external DTD subset.  The document can
> still be standalone="yes", so in principle we can't put these in the
> canonical form unless *require* processors to read the
> external subset.
> So I see the following realistic options.  Let's hear opinions and
> nail this down next Wednesday.
> N2-a. Lose PIs from the canonical form entirely
> N2-b. Lose PIs that happen to be in external entities
> N2-c. Lose PIs that happen to be in the DTD, internal or external
> N2-d. Include all PIs, requiring canonicalizers to read all external
>       parts of the DTD.
> Note that both options b and c require information that is not
> currently provided by the infoset, so we have some liaison work to do.
> I must say that the more I think about this, both selection criteria
> (it happens to be in the document entity vs. it happens to be
> in the DTD)
> seem unsatisfactory to me.
> N2-a and N2-D weren't brought up in the meeting, but the more
> I think about
> them, the more I prefer either of them to either of -b and -c.  I have
> an action item to ask the Infoset group about enhancing the
> PI information,
> but I'll hold on that in case this group suddenly develops
> wild enthusiasm
> either for N2-a or N2-d, which would make it unnecessary. -Tim
> [2]
> Date: Thu, 17 Jun 1999 09:47:13 -0700
> To: "XML Syntax WG" <w3c-xml-syntax-wg@w3.org>
> From: Tim Bray <tbray@textuality.com>
> Subject: C14n issue N4 - XML declaration?
> Status:  O
> Should the canonical form include the XML declaration?  Subsidiary
> question: if so, which of the encoding and standalone declarations
> should it include?
> Let's hear opinions and nail this down next Wednesday.
> Minor pro:
>  XML docs with XML declarations are more robustly interchanged
> Minor con:
>  A couple of dozen extra bytes
> Serious issue: if we include the XML declaration, that makes the
> version of XML part of the canonical form. The corollory is that
> should there ever be an XML 1.1 or 2.0, no XML 1.1/2.0 document
> can ever be canonically equivalent to any XML 1.0 document.  Is
> this a good or bad thing?
> Note: if we leave the XML Decl out, and specify that this C14n
> spec applies *only* to XML 1.0 documents, we can postpone the
> decision about whether XML1 and XML2 docs can ever be canonically
> equivalent to the time we write the XML2 c14n spec.  Sounds good
> to me. -Tim
> [3]
> Date: Thu, 17 Jun 1999 09:47:13 -0700
> To: "XML Syntax WG" <w3c-xml-syntax-wg@w3.org>
> From: Tim Bray <tbray@textuality.com>
> Subject: C14n issue N3 - c14n processor
> Status:
> Should we introduce the notion of a canonicalization processor in the
> C14n WD, and define an interface to it, maybe only a return value?
> One advantage is that since canonicalization can fail due to
> inaccessability
> of external entities, it might be nice to have a deterministic way to
> find out when this happens.  On the contra side, every new thing
> added to the spec increases complexity and the chance of introducing
> errors, and makes conformant interoperability harder to achieve.
> Let's hear opinions on this and try to nail it down next
> wednesday. -Tim
> _________________________________________________________
> Joseph Reagle Jr.
> Policy Analyst           mailto:reagle@w3.org
> XML-Signature Co-Chair   http://w3.org/People/Reagle/
Received on Monday, 21 June 1999 10:59:37 UTC

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