Just to add to this, I'm sure there's a program called 'md5sum' or similar that calculates a 128 bit MD5 checksum on its argument. This could be integrated fairly easily - as long as the judge trusts you not to just output a pre-calculated string (e.g. 'blitwrite ac3f:12d1:094b:c008:9a37:3827:5601:de6b') and actually checks the file in question...

Save the whales. Feed the hungry. Free the mallocs.