[NTG-context] PDF Signature Fields

Andreas Schneider aksdb at gmx.de
Thu Mar 10 11:04:17 CET 2016


Hello Hans,

after comparing eforms and the result of a document edited by Acrobat, 
the relevant portions in the spec (PDF 32000-1:2008) are:
Section 12.7.4.5, with tables 232 and 233.

 From what I see it should be possible to add a field /FT /Sig with and 
without a /Lock dictionary.
The /Lock dictionary created by Acrobat also specifies the optional 
/Type /SigFieldLock (eforms doesn't, but when in doubt, I trust Adobe 
more than eforms ;-))

Here is an example from the PDF stream of a document manually forged 
with Acrobat:
%% Object stream: object 167, index 37; original object ID: 475
<<
   /AP <<
     /N 188 0 R
   >>
   /DA (/Helv 0 Tf 0 g)
   /F 4
   /FT /Sig
   /Lock 187 0 R
   /MK <<
   >>
   /P 196 0 R
   /Rect [
     253.965
     163.306
     525.056
     186.143
   ]
   /Subtype /Widget
   /T (Gehnehmiger Unterschrift)
   /Type /Annot
>> 
%% Object stream: object 187, index 57; original object ID: 495
<<
   /Action /Exclude
   /Fields [
     (Einrichter Name)
     (Einrichters Unterschrift)
   ]
   /Type /SigFieldLock
>> 

("Einrichter Name" is another Text Field --> /FT /Tx [...] /Subtype 
/Widget [...] /T (Einrichter Name)
  "Einrichters Unterschrift" is another Signature Field)

Best regards
Andreas


Am 2016-03-09 16:16, schrieb Hans Hagen:
> On 3/9/2016 2:11 PM, Andreas Schneider wrote:
>> Hello all,
>> 
>> is there currently any mechanism in ConTeXt similar to the LaTeX 
>> digsig
>> or eforms package?
>> I want to add a form field that can be digitally signed (which is now
>> already possible with Acrobat Reader, not just with Acrobat Pro).
>> 
>> Additionally (like the mentioned eforms package) it would be nice, if
>> you could specify other form fields that should be locked once the
>> signature field is actually signed (according to the PDF spec this is
>> simply set via a dictionary).
> 
> it's probably something trivial to implement so what are the relevant
> fields (paragraphs/tables/dics/fields in the pdf spec) .. i'm not
> going to reverse engineer some package but start from the spec
> 
>> Anyway: can this currently be achieved with ConTeXt? If not: is there
>> any chance to get that feature added sometime? :-)
> 
> so far i never bothered with anything signature (i must say that i
> never ran into such docs and it would not make them more valid to me
> anyway)
> 
> Hans
> 
> -----------------------------------------------------------------
>                                           Hans Hagen | PRAGMA ADE
>               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>       tel: 038 477 53 69 | www.pragma-ade.com | www.pragma-pod.nl
> -----------------------------------------------------------------


More information about the ntg-context mailing list