\documentclass{article}
\input{6824-preamble}

\begin{document}
\psetnum{9}
\date{2005/03/15}

\begin{pset}
  The system is attackable if users can generate their own
  public/private keypairs, so it must not be possible to do so; the
  only valid keypairs must be those hard-coded into the XOM
  chips. The vendor of the XOM chips can indicate which are valid,
  perhaps by distributing a list of valid keys to software vendors, or
  by signing chips' public keys with some trusted master key. Then
  users will not be able to decrypt the software directly (without the
  XOM chip) unless they can physically extract the private key from
  the chip (and if they can do this, then many other attacks are also
  possible.)
\end{pset}
\end{document}