Is there any easy way totrick someone by making a replaced file have the same md5 sum by adding in useless bits at the end or something?
md5 is a cryptographic hash function. These functions do exactly have the property that no two messages (files) should have to the same checksum. [All cryptopeople, please excuse my loose argumentation. I know, I should argument on things like preimage resistance and collosion resistance. I like to put it the easy way here!] It would take you an aweful long time to find two files which map to the same hashvalue. Especially it might not be possible to pad a file with anything to get the same values! See Handbook of Applied Cryptography for further details about hashfunctions and MD5 in general. Cheers Raffy