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Re: [widgets] Jar signing vs. XML signatures

From: Thomas Roessler <tlr@w3.org>
Date: Tue, 14 Apr 2009 12:01:39 +0200
To: Henri Sivonen <hsivonen@iki.fi>
Message-Id: <6344D556-5F3E-438A-BBD4-763BDF2060E2@w3.org>
Cc: public-webapps <public-webapps@w3.org>
On 14 Apr 2009, at 11:42, Henri Sivonen wrote:

> I don't find the string anyURI in the spec, but anyURI is a great  
> example of why defining syntax in terms of XSD datatypes is a bad  
> idea:
> http://hsivonen.iki.fi/thesis/html5-conformance-checker#iri

anyURI is used in XML Signature.  I don't know off-hand whether or not  
it's used within the widget signature profile.

> XSD datatypes are too vague, allow whitespace where the spec writer  
> didn't mean to allow whitespace or allow surprising values (like "0"  
> and "1" when the spec writer though (s)he'd be allowing "true" and  
> "false"). It is much safer to define datatypes in precise English  
> prose like HTML5 does than to expect XSD to match what is really  
> meant.

There's an interesting discussion to be had here; however, I doubt  
it's in scope for this WG.  (In other words, this strikes me as a  
rathole.)

>>> When you need to reserialize XML, you import all the troubles of  
>>> serializing XML (see e.g. https://issues.apache.org/bugzilla/buglist.cgi?query_format=advanced&product=Security&component=Canonicalization&cmdtype=doit 
>>>  ).
>>
>> The only place where you actually need canonicalization is when  
>> hashing the SignedInfo element inside the signature file (i.e.,  
>> once per signature verification).
>>
>> Given that the signature format is profiled down pretty heavily in  
>> the widget signing spec, I'd dare a guess that most of the  
>> complexity isn't ever used, so a careful implementation might be  
>> able to write a c14n implementation that bails out on anything that  
>> doesn't look like a signature that follows the constraints in this  
>> format.
>
>
> If you need to do canonicalization even in one place, you need a  
> properly debugged implementation of it. If the signature format is  
> profiled heavily, doesn't it mean you can't even use an off-the- 
> shelf implementation of XML signatures?

Much of the complexity of canonicalization (and signature in general)  
comes from the need to deal with pretty arbitrary nodesets generated  
by transform chains.  The widget signature profile does not use (i.e.,  
it's a MUST NOT) any transform chains.

Since the use of transforms is a choice of the signature application,  
you shouldn't have any trouble using existing toolkits.
Received on Tuesday, 14 April 2009 10:01:49 GMT

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