You can't "encrypt" nif files because in order to use your encrypted files the engine that uses them would need to know how to "decrypt" them.
If you care about people copying the contents of your files, you have to manage where you distribute your files, i.e an encrypted zip file?
At that point its really an issue of trust. Who you trust with the files, how how people can get access to them, etc.
We only deal with giving people the ability to make content, what people do with that as owners of the content is left in their control, not ours.
Unfortunately your dealing with the human element at that point, which isn't something we have to cater for as open source software
Also please do not post duplicate topics.