Module::Signature adds cryptographic authentications to CPAN
distributions, via the special SIGNATURE file.

If you are a module user, all you have to do is to remember
running "cpansign -v" (or just "cpansign") before issuing
"perl Makefile.PL" or "perl Build.PL"; that will ensure the
 distribution has not been tampered with.

For module authors, you'd want to add the SIGNATURE file to
your MANIFEST, then type "cpansign -s" before making a distribution.