problems with signature fields

problems with signature fields

[Pablo Rodriguez]

Hans,

I have the following sample:

  \setupinteraction[state=start]

  \starttext
  \startTEXpage[offset=1em]
       \definefield[x][signature]
       \field[x]
  \stopTEXpage
  \stoptext

I can only use Acrobat to sign PDF documents with signature fields
generated by ConTeXt. Other tools sign the PDF document not producing a
valid signature (Acrobat cannot read or validate it).

From the source, signature has two objects (copied from the sample above):

  2 0 obj
  <<
    /DA (/rmtf 11.9552 Tf 1.1955 Ts 0 0 0 rg 0 0 0 RG)
    /DV <FEFF>
    /F 4
    /FT /Sig
    /Ff 0
    /Kids 1 0 R
    /MaxLen 1024
    /Q 0
    /Subtype /Widget
    /T <FEFF0078>
    /V <FEFF>
  >>
  endobj

  4 0 obj
  <<
    /Type /Annot
    /DA (/rmtf 11.9552 Tf 1.1955 Ts 0 0 0 rg 0 0 0 RG)
    /F 4
    /Parent 2 0 R
    /Q 0
    /Subtype /Widget
    /Rect [ 14.033054 14.033054 70.40415 25.08072 ]
  >>
  endobj

One of the tools that has issues with two objects for the signature
field is the latest version (1.18) from mupdf-gl.

mupdf-gl adds the signature value to the child (object 4) and not to its
parent (object 2).

I’m afraid this is also the same issue that AutoFirma (a e-signing tool
developed by the Spanish government
[https://firmaelectronica.gob.es/Home/Descargas.html]) has with these
signature fields.

When both objects are merged in one (as Acrobat Reader does when saving
a copy), both tools generate documents contaning signatures totally
unproblematic to be read validated by Acrobat.

I suggested merging both objects back in 2017. You told me that
simplifyng this would introduce too much complexity in ConTeXt only to
save some bytes.

Back then, I thought it was an minor improvement. Now I realized that
this two objects for signature fiels are only valid for Acrobat.

I wonder whether this improvement might be also easier to make in LMTX.

Would it be possible that signature fields may have only one object, so
that mupdf-gl and other tools have no problem signing fields PDF
documents generated by ConTeXt?

Many thanks for your help,

Pablo
--
http://www.ousia.tk
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Re: problems with signature fields

[Hans Hagen]

On 11/11/2020 9:46 PM, Pablo Rodriguez wrote:
> Hans,

> Back then, I thought it was an minor improvement. Now I realized that
> this two objects for signature fiels are only valid for Acrobat.

te hother tools hould be fixed ... indirect objects are pretty valid

> I wonder whether this improvement might be also easier to make in LMTX.

not without changing the implementation of fields (which makes no sense 
... in fact one can start to wonder about widgets of any kind now that 
flash is dropped which is needed/used for rendering of some image types 
in pdf)

> Would it be possible that signature fields may have only one object, so
> that mupdf-gl and other tools have no problem signing fields PDF
> documents generated by ConTeXt?
all is possible but i'm not sure if i want to uglify the implementation 
for the sake of buggy viewers

Hans

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Re: problems with signature fields

[Pablo Rodriguez]

On 11/12/20 12:24 AM, Hans Hagen wrote:
> On 11/11/2020 9:46 PM, Pablo Rodriguez wrote:
>> Hans,
>
>> Back then, I thought it was an minor improvement. Now I realized that
>> this two objects for signature fiels are only valid for Acrobat.
>
> the other tools should be fixed ... indirect objects are pretty valid

Many thanks for your reply, Hans.

I totally agree, these tools need to be fixed.

I reported the issue to one of the projects more than two years ago. I’m
still waiting for a message about the issue report.

>> Would it be possible that signature fields may have only one object, so
>> that mupdf-gl and other tools have no problem signing fields PDF
>> documents generated by ConTeXt?
> all is possible but i'm not sure if i want to uglify the implementation
> for the sake of buggy viewers

In Windows (and I guess in macOS), saving a copy with Acrobat Reader DC
seems to unify both objects.

But I’m afraid Acrobat for Linux is too old for that (9.5.5).

Many thanks for your help,

Pablo
--
http://www.ousia.tk
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