Come on, man. I thought there could be a built in fuction or a core module that can deal with crc-stuff since it is so common task now a day.

There are many common tasks, not everything is in core....

CRC site:perldoc.perl.org ► http://perldoc.perl.org/Compress/Zlib.html

You don't need to give me a lecture on how to use cpan nor on why reinventing will sucks:)

Well :D two sentences don't make a lecture, though it does appear you need it :)