Re: [Podofo-users] digital signatures

[Alvaro C. <alv...@gm...>]

Hello Leonard, thanks for your reply. What do you think about the next code?
bool isSignatureField(const PdfMemDocument &doc, const PdfObject *const pObj)
{
   if (pObj == 0) return false;
   if (not pObj->IsDictionary()) return false;

   const PdfObject *const keyFTValue =
pObj->GetDictionary().GetKey(PdfName("FT"));
   if (keyFTValue == 0) return false;

   string value;
   keyFTValue->ToString(value);
   if (value != "/Sig") return false;

   const PdfObject *const keyVValue =
pObj->GetDictionary().GetKey(PdfName("V"));
   if (keyVValue == 0) return false;

   const PdfObject *const signature =
doc.GetObjects().GetObject(keyVValue->GetReference());
   if (signature->IsDictionary()) return true;
   else return false;
}

int getNumberOfSignatures(const PdfMemDocument &doc)
{
   /// Find the document catalog dictionary
   const PdfObject *const trailer = doc.GetTrailer();
   if (not trailer->IsDictionary())
       throw std::invalid_argument("Document invalid, non-dictionary trailer!");

   const PdfObject *const catalogRef =
trailer->GetDictionary().GetKey(PdfName("Root"));
   if (catalogRef==0 or not catalogRef->IsReference())
       throw std::invalid_argument("Invalid /Root entry");

   const PdfObject *const catalog =
doc.GetObjects().GetObject(catalogRef->GetReference());
   if (catalog==0 or not catalog->IsDictionary())
       throw std::invalid_argument("Invalid or non-dictionary
referenced by /Root entry");

   /// Find the Fields array in catalog dictionary
   const PdfObject *acroFormValue =
catalog->GetDictionary().GetKey(PdfName("AcroForm"));
   if (acroFormValue == 0) return 0;
   if (acroFormValue->IsReference())
      acroFormValue = doc.GetObjects().GetObject(acroFormValue->GetReference());
   if (not acroFormValue->IsDictionary()) return 0;

   const PdfObject *fieldsValue =
acroFormValue->GetDictionary().GetKey(PdfName("Fields"));
   if (fieldsValue == 0) return 0;
   if (fieldsValue->IsReference())
      fieldsValue = doc.GetObjects().GetObject(acroFormValue->GetReference());
   if (not fieldsValue->IsArray()) return 0;

   /// Verify if each object of the array is a signature field
   int n = 0;
   const PdfArray &array =fieldsValue->GetArray();
   for (unsigned int i=0; i<array.size(); i++) {
      const PdfObject *const obj =
doc.GetObjects().GetObject(array[i].GetReference());
      if (isSignatureField(doc, obj)) n++;
   }

   return n;
}

I tested it with some pdf files and it seems to work correctly, but I
am not sure about its completeness (sorry but I am newbie using podofo
and the pdf standard).

-
Alvaro
On 30 December 2011 14:51, Leonard Rosenthol <lro...@ad...> wrote:
> You have to iterate over all the fields in the Fields array in the AcroForm dictionary looking for those of type Sig.
>
> Of course, that will only tell you the number of signature fields.  For each field, you'll need to see if it's signed or not.
>
> Leonard
>
> -----Original Message-----
> From: Alvaro Cuno [mailto:alv...@gm...]
> Sent: Friday, December 30, 2011 10:10 AM
> To: pod...@li...
> Subject: [Podofo-users] digital signatures
>
> Hi,
>
> Is it possible to obtain the number of digital signatures in a pdf file directly? How can get a reference for them?
>
> -
> Alvaro
>
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