I am making a grease-monkey plugin for a website that has many flash files. I'd like to make a hash of the flash, the problem is that the flash files are up to 10(total) * 10MEGS. This is slow; I'd like to be able to only grab the first 80KB to hash. The end result would be an easy way to blacklist certain flash files containing unwanted content. Is this possible? Suggestions? Code examples are greatly appreciated!