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Re: Enveloped signatures

From: Joseph M. Reagle Jr. <reagle@w3.org>
Date: Wed, 10 May 2000 08:29:00 -0400
Message-Id: <>
To: Petteri Stenius <Petteri.Stenius@remtec.fi>
Cc: "IETF/W3C XML-DSig WG (E-mail)" <w3c-ietf-xmldsig@w3.org>

At 11:35 2000-05-10 +0300, Petteri Stenius wrote:
 >6.6.5 Signature Exclusion
 >    http://www.w3.org/2000/02/xmldsig#exclude-signature
 >The transform excludes the ancestor Signature element of the DigestValue
 >element that is being calculated. The intention is to support enveloped
 >signatures where the DigestValue calculation would overlap with itself.

Petteri, the idea was that it would be somewhat elegant if we specified the
identifier and defined its behavior using an XPath expression (the
equivalent of your natural language text above). That way, people that don't
expect to implement XPath can implement the feature rather simply; those
that already have XPath don't have to do something special, and both will

The challenge then is to find the XPath equivalent of your description
above. This seemed to be potentially tricky in that the context node in your
description above is "the ancestor Signature element of the DigestValue
element that is being calculated" and if you go the XPath/XML route, it
isn't going to know this (what is being calculated), you just hand it XML.
Then the XPath processor sets the context node at the root root, and then
you have to specify an expression that finds and excludes the right
Signature (if they are nested.) There might be a clever way to do this
though, and I think Boyer might've mentioned you might be able to achieve
this by passing arguments from a function ... ? But we concluded by saying
let's give it some thought and discuss it on the list.

At the meeting, we had agreement to include this feature in the Candidate
REC / Proposed Draft, I'm waiting/hoping/thinking about if we can define it
as an XPath expression as well.

Joseph Reagle Jr.   
W3C Policy Analyst                mailto:reagle@w3.org
IETF/W3C XML-Signature Co-Chair   http://www.w3.org/People/Reagle/
Received on Wednesday, 10 May 2000 08:30:04 UTC

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