Thk perlfan too, other very well suggestion is use "hash of the reverse of the file" I dont thinking in that but is really good.

Please note that CRC is mostly used to check transmition but in fact the CRC is a "simple" method to transform any size of input data in a fix integer size, not less, not more, you can use that to anything that you want.

The bad think about this it's very short an can be colition.

Thk a lot to all.