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Posted to users@pdfbox.apache.org by Jonathan Barbero <jo...@gmail.com> on 2016/10/29 16:47:49 UTC

Detect modifications between signatures

Hi,

 How could I detect any modification between two signatures (visibles or
not) ?

For example:

 An application signs a PDF with PDFbox. A user downloads it, and should
sign it (visible signature). I would like to check that the user didn't add
any modification after the app signature (except it's own user signature).

How could I check it? I guess it's different between a visible signature
and not visible.

Thanks in advance,
 Jonathan.

Re: Detect modifications between signatures

Posted by Jonathan Barbero <jo...@gmail.com>.
Hi Tilman,

 Yes, I want to do that.
I'm going to look at the COS tree structure.

Thanks!

On Wed, Nov 2, 2016 at 4:10 PM, Tilman Hausherr <TH...@t-online.de>
wrote:

> Am 29.10.2016 um 18:47 schrieb Jonathan Barbero:
>
>> Hi,
>>
>>   How could I detect any modification between two signatures (visibles or
>> not) ?
>>
>> For example:
>>
>>   An application signs a PDF with PDFbox. A user downloads it, and should
>> sign it (visible signature). I would like to check that the user didn't
>> add
>> any modification after the app signature (except it's own user signature).
>>
>> How could I check it? I guess it's different between a visible signature
>> and not visible.
>>
>
> I assume that what you want is to have something similar to Adobe Reader,
> which can detect whether users did more than just add a signature, and then
> tells "page X was changed".
>
> I can't think of a way to do this out of the box. Maybe compare the COS
> tree of both PDF structures.
>
> Tilman
>
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Re: Detect modifications between signatures

Posted by Tilman Hausherr <TH...@t-online.de>.
Am 29.10.2016 um 18:47 schrieb Jonathan Barbero:
> Hi,
>
>   How could I detect any modification between two signatures (visibles or
> not) ?
>
> For example:
>
>   An application signs a PDF with PDFbox. A user downloads it, and should
> sign it (visible signature). I would like to check that the user didn't add
> any modification after the app signature (except it's own user signature).
>
> How could I check it? I guess it's different between a visible signature
> and not visible.

I assume that what you want is to have something similar to Adobe 
Reader, which can detect whether users did more than just add a 
signature, and then tells "page X was changed".

I can't think of a way to do this out of the box. Maybe compare the COS 
tree of both PDF structures.

Tilman

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