Crypt::License decodes an encrypted file and attempts to decrypt it by first,
looking for a hash pointer in the caller program called $ptr2_License. The
hash contains the path to the License file and an optional 'private' key list
of modules which will decrypt only with the 'private' key. OR, a hash key of
'next' with no particular value that indicates to look to the next caller on
the stack for the License pointer. If the pointer is not present or the
License file is not found successfully, then no further action is taken. If the
License file is successfully opened, and the contents validated then the
attached encrypted module is loaded and the seconds remaining until License
expiration are returned or now() in the case of no expiration. Undef is
returned for an expired license (module fails to load).

WWW: http://search.cpan.org/dist/Crypt-License/