Hey. So this is a project that I slapped together in an evening - it performs an exceptionally simple encryption / decryption for blend files real-time, meaning it's a (very small) extra step to prevent users from opening your externally packed blend files.
The BlendCrypt script has an Encrypt function that turns the blend file into a binary text file and writes a custom key string that you can change into it. When you want to, you can decrypt the file using only the same script that encrypted it (that has the same keystring), and then play the game. Once you're done, the file is re-encrypted, keeping people from being able to open it with Blender or even append any resources from it. The only fault is that between encrypting and decrypting, the file is wide open; still, it's better than nothing (LOL). Anyway, here's the link to the BlendCrypt Download.