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Re: Scenarios/FAQ

From: Andreas Schmidt <aschmidt@darmstadt.gmd.de>
Date: Tue, 18 Jan 2000 11:19:56 +0100
Message-ID: <38843E4C.EBE5AAC8@darmstadt.gmd.de>
To: John Boyer <jboyer@uwi.com>
CC: DSig Group <w3c-ietf-xmldsig@w3.org>
John Boyer wrote:

> Joseph asked for this to be posted for consideration before the FTF.
> This is a first draft of (some of) the questions that will end up in the new
> scenarios/FAQ document.  In addition, rough notes on what the answers will
> be are given.
> Please feel free to comment on these answers.  Also, certainly there are
> additional useful questions/answers.

I want to briefly comment on FAQs 2) and 5) cited below

> 2) I have a whole XML document.  How do I sign it?
> A1: If the XML document is addressable by a URL, then you could create a
> detached signature. The SignedInfo Reference would include a URI to the XML
> document.
> A2: If you have a copy of the XML document in some temporary file or memory
> buffer, you can put the data in an enveloping signature.  It is likely that
> you will have to base-64 encode the XML document since an entire XML
> document cannot appear as element content.  Alternately, character sequences
> forbidden from content by XML can be escaped using the XML escaping
> mechanism.
> A3: You could create an enveloped signature inside the XML document. The
> SignedInfo Reference would refer to the document’s root element.  The
> signature would have to use transforms to excluded itself from the message
> digested in the Reference’s DigestValue.


> 5) I have an XML document.  How do I combine that document with a signature
> such that, in the resulting document, the signature signs the original
> document?
> A1: Create an enveloping signature around the root element of the document.
> A2: Create an enveloped signature.  The signature is placed inside the
> document, and its SignedInfo Reference contains transforms that omit the
> signature from the document.

First it seems to me, that these two could be combined into a single
question (maybe with subpoints). Two suggestions, that I think would help
the issues:

1. In answers 2) A3 and 5) A2 the _minimum_ content to be omitted by the
transformations (DigestValue and SignatureValue), and that it MUST be omitted
for the signature to validate
should be clearly stated (since I think FAQs are for the non-expert). Editorial:
The URI="" addressing method should be spelled out and a reference to the
defining portion of the spec
should be given.

2. In [1] I made the suggestion that URI="" should automatically omit the stuff
leading to self-referentiality, which was objected in [2,3]. I would suggest
that the design choice
taken for core syntax behaviour is explained at this point (I think including
such stuff in a FAQ
helps clarifying and is therefore generally a good thing). Text proposal:

  "This two step procedure, using URI="" and transformations, has been
prescribed in spite of
    its apparent redundancy for the following reasons: ..."

The reasons given in [2,3] are to be filled in for ...

[1] http://lists.w3.org/Archives/Public/w3c-ietf-xmldsig/2000JanMar/0004.html
[2] http://lists.w3.org/Archives/Public/w3c-ietf-xmldsig/2000JanMar/0005.html
[3] http://lists.w3.org/Archives/Public/w3c-ietf-xmldsig/2000JanMar/0006.html

Received on Tuesday, 18 January 2000 05:18:32 UTC

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