{\TeX\ and controlled access to information}
{Boris Veytsman}
{While we in the \TeX\ community usually strive to make information open, there
are cases when controlling access to information is legitimate.  We do
not want to publish our passwords, medical histories and other
sensitive details.  Sometimes the information is not confidential, but
different audiences require different levels of detail: consider
students' and teachers' versions of a textbook.

There are two approaches to this problem in \TeX.  Output-level access
control means that we have a single \TeX\ source which can produce
different \PDF\ files depending on the compilation options.  In some
cases we need source-level access control, when we distribute different
versions of \TeX\ file obtained from the same master source.

In this talk we discuss the tools for both these approaches and their
implementation in a \TeX\ system.}