Generic Counter Mode implementation in pure Perl. The Counter Mode module
constructs a stream cipher from a block cipher or cryptographic hash funtion
and returns it as an object. Any block cipher in the Crypt:: class can be
used, as long as it supports the blocksize and keysize methods. Any hash
function in the Digest:: class can be used, as long as it supports
the add method.

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