digsig.sty

%******************************************************************************
% File:     @(#)$OrigId: digsig.sty,v 1.16 2015-06-07 08:57:00+02 martin Rel $
% Contents: LaTeX macros for digital signature fields in PDF files
% Author:   Martin Lottermoser, Braunschweig, Germany;
%	    Martin.Lottermoser at t-online.de
%
%******************************************************************************
%
%	Copyright (C) 2005-2015 by Martin Lottermoser
%	All rights reserved
%
%******************************************************************************
%
% This package is an extension of the "hyperref" package and depends on
% internal interfaces and other properties of that package which are not
% documented and hence might change without notice.
%
% To use this package, proceed as follows:
% - Include "\usepackage{digsig}" in your document. If it has not happened yet,
%   this call will also pull in the "hyperref" package. If you want to specify
%   options in the \usepackage call for "hyperref", include that package before
%   including "digsig".
% - Call the macro \digsigfield to create one or more signature fields. The
%   macro's interface is specified below before its definition.
% - The region of your file where you call \digsigfield should be contained in
%   hyperref's "Form" environment.
% - For generating a PDF file, use either pdfTeX or configure hyperref for a
%   DVI driver (e.g., dvips) for which hyperref supports the \pdfmark command.
%   Using other configurations will not lead to signature fields; this package
%   will issue warnings in this case.
%
% To insert a signature in a signature field, you will also need suitable
% software and, of course, a key. Note that Adobe's free Acrobat Reader is
% capable of signing a signature field in a normal PDF file only since
% version 11.0.7 (May 2014).
%
%
% License
% =======
% It cannot be applied exactly, but you should consider this file to be usable
% in the spirit of the GNU Lesser General Public License, version 2.1
% (LGPLv2.1; see http://www.gnu.org/licenses/lgpl-2.1.html). Basically, I do
% not claim to have any rights in the documents you create with this software,
% you don't have to distribute my macros with your documents, but if you copy
% or modify the macros and offer this derived version for distribution you have
% to do this under the same license and it must be apparent what you have
% copied or modified.
%
% If you have questions concerning this license, contact me for clarification.
%
%******************************************************************************

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{digsig}[2015/06/07 Digital signature fields for PDF]

%******************************************************************************

% No options
\ProcessOptions

%******************************************************************************

% We need the hyperref package.
\RequirePackage{hyperref}

%******************************************************************************

% Macro \digsigfield for creating a PDF signature field, similar in effect to
% hyperref's \TextField etc. macros. Its arguments are:
%   #1: field width
%   #2: field height
%   #3: name of the field; may not contain periods ("."). This is not visible
%	in the printed representation but is usually displayed in a PDF viewer
%	capable of creating or verifying signatures. It depends on internals of
%	the "hyperref" package what happens if you use characters outside the
%	set of printable characters from ISO 646 (vulgo ASCII) or combining
%	control sequences like '\"'. My advice is to first ignore this
%	question, choose a sensible name encoded in your input encoding, and
%	then check the name displayed by your PDF reader. Change and repeat
%	until the result is more or less satisfactory :-).
% From the point of view of TeX, the macro creates an empty box of the
% specified extension with its reference point in the lower left corner.
% Note that the macro does not change TeX's mode; if you want to enforce
% horizontal mode for the environment the box is placed in, you will have to
% take suitable steps yourself before calling the macro.
%
% Until it has been filled in, the field will only become visible in a PDF
% viewer aware of signature fields. Signature-generating software will usually
% create something to appear in the printed representation when you sign the
% field. You can generate a signature field where the signature will not become
% visible on the page by specifying a box of zero width and height. (This is
% not as trivial as it sounds.) However, keep in mind that this field is only
% invisible to the viewer; in terms of TeX, it's a box and may influence
% formatting, in particular in the vertical modes.
%
% The following is an example of a call:
%
%   \begin{Form}
%     \digsigfield{5cm}{2cm}{Author's signature}
%   \end{Form}
%
\newcommand*{\digsigfield}[3]{\hbox{%
  \pdfstringdef\Fld@name{#3}%
  \def\Fld@align{1}%	Is this sensible? Do we need an option?
  \Fld@hiddenfalse
  \dimen255=#1\relax\ifdim\dimen255 < 2sp
    \dimen255=#2\relax\ifdim\dimen255 < 2sp \Fld@hiddentrue \fi\fi
    % No cheating with negative values! :-)
  \setbox0=\hbox{\rule{0mm}{#2}\kern#1}%
  % There has been an unfortunate (and in my opinion ill-considered) change
  % between pdftex 1.10b and pdfetex 1.21a: while \pdfstartlink/\pdfendlink
  % could formerly be called if \pdfoutput was zero, this is no longer
  % permitted in the newer versions. Hence the following is needed twice:
  \def\helper{\expandafter\ifx\csname pdfmark\endcsname\relax
      \box0\PackageWarningNoLine{digsig}{No pdfmark support in selected
	hyperref driver, hence no signature field ``\Fld@name''}%
    \else
      \pdfmark[\box0]{pdfmark=/ANN,Raw={\PDFFormExtension@Signature}}%
    \fi
  }%
  \expandafter\ifx\csname pdfoutput\endcsname\relax
    \helper
  \else\ifnum\pdfoutput > 0
    \pdfstartlink user {\PDFFormExtension@Signature}\box0\pdfendlink
  \else
    \helper
  \fi\fi}}

% Internal macro, similar to the \PDFForm@* macros of hyperref. The omission of
% parameterization for "MK" is deliberate: if you need a border, create it with
% TeX.
\newcommand{\PDFFormExtension@Signature}{%
  /T (\Fld@name)
  /Subtype /Widget
  /FT /Sig
  /F \ifFld@hidden 2\else 4\fi\space
  /Q \Fld@align\space
  /MK << /BC [] >>}

%******************************************************************************

% Record version information for this package if possible
{\expandafter\ifx\csname sourceidentification\endcsname\relax\else
  \sourceidentification{\whatstring
    $OrigId: digsig.sty,v 1.16 2015-06-07 08:57:00+02 martin Rel $}
\fi}

%******************************************************************************

\endinput