As far as checksum, it might be CRC32, or they may be reading a hash value like MD5 or SHA-1. If it is SHA-1, forget about cracking it.
Trying to force a checksum or hash on a file period is damn near improbable. I'm not sure about CRC32 or MD5, but SHA-1 is, if I'm not mistaken, birthday attack-proof (or at least resistant)...that kills off a faster way of finding two known values that produce the same hash. All I will say is that it most likely won't happen in at least our lifetime.
This post has been edited by EvilWays: Feb 8 2004, 04:53 AM