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Re: XForms and XML Signatures : How to get the presentation layer?

From: David Landwehr <david.landwehr@picoforms.com>
Date: Wed, 20 Jun 2007 10:36:05 +0200
Message-ID: <4678E6F5.8030704@picoforms.com>
To: duryodhan <duryodhan125@gmail.com>, www-forms@w3.org

Hi,

I did not reply to the list because you did not in your reply to me ;-)

I'm sorry if I'm starting to iterate or write about something you 
already is aware of or other did write to you about, however here it 
comes: It is clear what is to be signed has to be displayed to the user 
to make sure he knows what he is signing. Depending on legal stuff in 
the country and what the application needs there might be strict 
requirements to the signature and the content. E.g. some countries 
requires that the signature is composed of the bitmap for what is 
signed, this is e.g. what adobe reader is doing and I would guess Dr. 
Boyer's implementation as well. Only by having the bitmap you will be 
certain what was presented to the user (corner cases could here be that 
the TFT screen had a bunch of fallouts and therefore the user did not 
see some part of the screen, but legaly that would not hold). When 
signing xhtml+xforms you will soon discover that presenting this to the 
user to be sure what he is signing is difficult, e.g. CSS styling might 
hide fields depending on states and so (or styling could obscure some 
part of the screen e.g. with overflow or fixed boxes). Also with firefox 
you might have a shadow DOM and other pieces of information wich is in 
or not in the DOM. So considering this it seems to be quite problematic 
to solve the signing problem in an elegant way in XForms simply because 
signing is actual about presentation and not so much about the data 
being signed. A note here is that it is not enough simply to sign the 
bitmap without signing the data along with it, as the system also have 
to be sure what the user signed (e.g. if the user can sign a bitmap and 
not the data he might be able to signed a bitmap and submit it to the 
server with some other kind of data which the server cannot likely 
validate since it will not be able to read the bitmap, but I guess I 
would not have needed to explain this)...

Now I was writing this I came up with an idea for what would be a good 
solution in Firefox. Firefox implements the canvas element which is 
actually able to catch part of the screen as bitmap and display it to 
the user. It is also able to convert the bitmap to base64. So you could 
implement the bitmap approach in Firefox... Let me know if you want to 
explore this option and I will eloborate.

Best regards,
David


duryodhan skrev:
> Hey,
>
> Oops! Sorry about that!
>
> I was talking not about the XForms recommendation but the stuff
> reported in 
> http://2006.xmlconference.org/programme/presentations/100.html
>  and also the 
> http://www.xsmiles.org/presentations/conference/signed_forms_pres_icwe2005.pdf 
>
>
> As authors of both are reputed members of the forms WG , I thought it
> was part of the recommendation. On checking , it seems I am wrong.  I
> am sorry for my oversight. But anyways, you have inlcuded the first
> link in the main page of your WG page, I was hoping that you all had
> already come up with an example of what to sign and what not to
> sign....
>
> Is anyone clear as to what needs to be signed and an example of it for
> XForms with XHTML doc?
>
>> I'm puzzled about you writing "Aren't the concerns you are raising valid
>> over there too? "
>
> I was talking of "over there" as in the WG recommendations / the
> presentations , not the geographical "over there". :D
>
> Why did you not reply to the list? Should I send this to the list or
> not ( I haven't as of now)?
>
> Regards,
> duryodhan


-- 
David Landwehr
Senior Product Architect
PicoForms
web:    http://www.picoforms.com
e-mail: david.landwehr@picoforms.com
phone:  +45 24 27 55 18
Received on Wednesday, 20 June 2007 08:36:52 GMT

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