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Re: Enveloped Signature Transform

From: Christian Geuer-Pollmann <geuer-pollmann@nue.et-inf.uni-siegen.de>
Date: Thu, 07 Feb 2002 14:17:52 +0100
To: Mauro Arcolini <arcolini@sec.di.unipi.it>, w3c-ietf-xmldsig@w3.org
Message-id: <3774158071.1013091472@crypto>


--On Donnerstag, 7. Februar 2002 11:48 +0100 Mauro Arcolini 
<arcolini@sec.di.unipi.it> wrote:

>
> Example:
>> <test:a ...>
>>   ...
>>   <ds:Signature ... >...</ds:Signature> <!-- first signature refers to
>> test:a -->    <ds:Signature ... >...</ds:Signature> <!-- second signature
>> refers also to test:a -->  </test:a>
>>
>> Both of these signatures contain enveloped transform and refer to the
>> same "test:a" element.  According to the specification the first
>> signature should sign the second one and the second one should sign the
>> first.  The same problem arise during verification phase. Is there any
>> reccomendation for this case?
>
>>> When you add sig1 to the document, you sign the document (which does
>>> include sig1 and the data) and exclude sig1. Then you add sig2 which
>>> signs  the document (data + sig1 + sig2) and then exclude sig2;
>
>>> Verification of sig2 will work ok, but verification of sig1 fails: You
>>> verify the document (data + sig1 + sig2) and exclude sig1. So you
>>> verify  (data + sig2) which was not signed (only data was signed).
>
>>> Solution: Use an XPath which omits all Signature, not only the current
>>> one.
> The XPath is only for the first ds:Signature??. If yes, there are no
> problem for verification  of the first ds:Signature, after adding other
> ds:Signature, but for the second ds:Signature?  The second ds:Signature
> signs also the first, but after adding other ds:Signature, the
> verification fails  Solution: For each ds:Signature use an XPath omits
> all ds:Signature added after.  But it really exists an XPath for this
> problem??

Sorry, I don't understand why the second signature has a problem? By adding 
the second signature to the content which is signed by the first signature, 
you break signature 1. The second signature covers the data _and_ the first 
signature.

Christian
Received on Thursday, 7 February 2002 14:17:16 GMT

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