pdfSecurity
I have recently been asked to add a digital signature to a report (which I wrote using pdflatex). Is there such a mechanism in the TeX/LaTeX world or am I better of using external software to verify the validity of the report.
I don't necessarily want to password protect the document…or prevent people from copying the text as they commissioned the report!
This may not be limited to TeX so my apologies if in the wrong forum…
According to the PDF specification (p. 446f), it is possible to specify the form fields that shouldn't be changed any more once a signature field has been signed in a so-called sigature field lock dictionary. With the eforms package, the code for your signature field in \mySigField to do this would be:
\sigField[\Lock{/Action/Include/Fields [(name#1)(pos#1)]}]{#1}{#2}{#3}
The names of the form fields that should be locked are given in round brackets. Other possible specifications are \Lock{/Action/All} to lock all form fields, and \Lock{/Action/Exclude/Fields [(field1)(field2)...]} to lock all fields apart from the specified ones.
In your example, the code above would specify non-existing form fields if one or both of the arguments for name and position are supplied, so it is possibly cleaner to use a series of conditions:
\ifthenelse{\equal{#4}{}}%
{\ifthenelse{\equal{#5}{}}%
{\sigField[\Lock{/Action/Include/Fields [(name#1)(pos#1)]}]{#1}{#2}{#3}}%
{\sigField[\Lock{/Action/Include/Fields [(name#1)]}]{#1}{#2}{#3}}%
}%
{\ifthenelse{\equal{#5}{}}%
{\sigField[\Lock{/Action/Include/Fields [(pos#1)]}]{#1}{#2}{#3}}%
{\sigField{#1}{#2}{#3}}%
}%
Unfortunately, I'm not able to test whether this works as expected, as I don't own Adobe Acrobat to actually fill one of the fields with a signature.
A quick solution, with pictures changed:
\documentclass{article}
\usepackage[draft]{graphicx}
\usepackage{url}
\begin{document}
\noindent \begin{tabular}{l l l}
CUSTOMER: & \includegraphics[width=6cm,height=1.5cm,keepaspectratio]{at} & Date: \\%{% now "SHORT_DATE_FORMAT" %}\\
& {\url{ qb_full_name|upper }} & \\
\end{tabular}
\begin{tabular}{l l l}
REP: & \includegraphics[width=6cm,height=1.5cm,keepaspectratio]{at} & Date: \\%{% now "SHORT_DATE_FORMAT" %}\\
& {\url{ qb_rep_name|upper }}
\end{tabular}
\bigskip
Second version:
\bigskip
\noindent \begin{tabular}{lc}
CUSTOMER: & \includegraphics[width=5cm,height=1.5cm]{at}\\
\cline{2-2}
& \multicolumn{1}{r}{ Date: 05/23/2013}
\end{tabular}
\hspace{1mm}
\begin{tabular}{l c}
REP: & \includegraphics[width=6cm,height=1.5cm]{at}\\
\cline{2-2}
& \multicolumn{1}{r}{\rule{0mm}{4mm} Date: 05/23/2013}
\end{tabular}
\end{document}
Two tables in one line. Package url for underline char. Frame around at.png is a picture. I have removed keepaspectratio to show the begaviour of Date: 05/23/2013, one of them with correction of depth.
Best Answer
I've asked question on other side about proving that file has not changed after given time.
It's slightly different than signatures, but IMHO very important aspect of checking validity of report: checking if it has not been changed after creation (and legally provable).
One way of protection are Cryptographic Timestamps.
There are mechanisms based on PKI and digital signatures supported by Adobe PDF.
I've found that Linked Hybrid schemes are most interesting and Keyless Signatures - Cryptographic Timestamps Guard-time Technology looks most intersting and promising with nice cross-platform desktop client and other tools.