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Re: Proposed requirements update related to prefix rewriting

From: Frederick Hirsch <Frederick.Hirsch@nokia.com>
Date: Fri, 23 Oct 2009 13:51:33 -0400
Cc: XMLSec WG Public List <public-xmlsec@w3.org>
Message-Id: <F12F6BC3-65F9-4903-93A4-B779553C21FD@nokia.com>
To: Hirsch Frederick (Nokia-CIC/Boston) <Frederick.Hirsch@nokia.com>
Here is an updated proposal to revise the requirements [1] for prefix  
normalization, taking into account xsi:type:

(1) Change the section titled "Relax certain guarantees" as follows:

Change section title to "Enable optional prefix rewriting" and change  
the text:

"A limited revised version of Canonical XML might be one in which  
namespace prefixes are not guaranteed to be preserved, possibly   
breaking the meaning of QNames."

to

"Canonical XML should support the option of namespace prefix re- 
writing, optionally including rewriting within xsi:type attributes as  
well. In the case of prefix rewriting namespace prefixes are not  
guaranteed to be  preserved, possibly breaking the meaning of QNames.   
The advantage of  using prefix rewriting is to avoid the complexity  
and confusion with prefixes used for different namespaces in different  
subtrees. This avoids mapping issues and the need for an  
implementation to store additional information for each node. When the  
prefix rewriting option is used, the xsi:type attribute may also have  
prefix rewriting as well. "

In section 4.4, "The Canonicalization Element" change #5 from

"5 preservePrefixes whether the prefix name is significant. When there  
are QNames in content, prefixes are probably significant, otherwise  
they could be expanded out into URIs or converted into n1. n2, n3 etc"

to

"5 preservePrefixes whether the prefix name is significant. When there  
are QNames in content, prefixes are probably significant, otherwise  
they could be expanded out into URIs or converted into n1. n2, n3 etc.  
Prefixes in xsi:type attribute values can also be rewritten when  
prefix rewriting  is performed if the xsiTypeAware option is set."

This should close ACTION-402.

regards, Frederick

Frederick Hirsch
Nokia

[1] http://www.w3.org/2008/xmlsec/Drafts/transform-note/Overview.html

On Oct 19, 2009, at 12:08 PM, Hirsch Frederick (Nokia-CIC/Boston) wrote:

> In my absence I received an action (ACTION-402) to update the
> requirements document for ISSUE-136.
>
> ISSUE-136 states: "Is normalization of prefixes a goal for 2.0 c14n"
>
> The 2.0 proposal supports normalization of prefixes as an option, see
> the prefixRewrite parameter described in the Canonical XML Version 2.0
> editors draft
>
> http://www.w3.org/2008/xmlsec/Drafts/c14n-20/#Canonicalization-Parameters
>
> That document also lists requirements, specifically:
> [[
>
> 1.4.3 Robustness
>
> Whitespace handling was a common cause of signature breakages. XML
> libraries allow one to "pretty print" an XML document, and most people
> wrongly assume that the white space introduced by pretty printing will
> be removed by canonicalization but that is not the case. This
> specification adds three techniques to improve robustness:
>
> 	 Remove leading and trailing whitespace from text nodes,
> 	 Allow for QNames in content especially in the xsi:type attribute,
> 	 Rewrite prefixes
> ]]
>
> To complete ACTION-402, I suggest the following requirements document
> changes to the XML Signature Transform Simplification: Requirements
> document
>
> http://www.w3.org/2008/xmlsec/Drafts/transform-note/Overview.html#id83777
>
> (1) Change the section titled "Relax certain guarantees" as follows:
>
> Change section title to "Enable optional prefix rewriting "
> Change
>
> "A limited revised version of Canonical XML might be one in which
> namespace prefixes are not guaranteed to be preserved, possibly
> breaking the meaning of QNames."
> to
>
> "Canonical XML should support the option of namespace prefix re-
> writing. In this case namespace prefixes are not guaranteed to be
> preserved, possibly breaking the meaning of QNames.  The advantage of
> using this option is avoiding the complexity and confusion of prefixes
> that are used for different namespaces in different subtrees, avoiding
> mapping issues and the need to store additional information for each
> node for this mapping."
>
>
>
>
> regards, Frederick
>
> Frederick Hirsch
> Nokia
>
>
>
Received on Friday, 23 October 2009 17:52:26 GMT

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