This is mainly just one of those 'I always wondered' things. How secure really is the 128-bit encryption offered in Disk Utility? Is it virtually impossible to crack? Somewhat difficult? How long would it take someone who really knew what they were doing? If anybody wants to try, I made a sample encrypted disk image. See if you can get into it. Its 2MB and you can download it here. After downloading, you'll have to take the .txt off the end of the filename so its just challenge.sparseimage. See if anyone can tell me whats inside.