\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{boxedalltt}
\@ifundefined{verbatim@processline}{\RequirePackage{verbatim}}{}
\def\boxedalltt{%
  \def\alltt@processline{%
    {\setbox0=\hbox{\the\alltt@line}%
    \hsize=\wd0 \the\alltt@line\par}}%
  \@minipagetrue%%%DPC%%%
  \@tempswatrue%%%DPC%%%
  \setbox0=\vbox\bgroup \alltt
}
\def\endboxedalltt{%
  \endalltt
  \unskip\setbox0=\lastbox %%%DPC%%%
  \egroup
  \fbox{\box0}% <<<=== change here for centering,...
}