I have a few questions about NSIS that have probably been answered (but my search has returned nothing).
1) Can NSIS pull data from a server on the internet?
2) Can NSIS work with encrypted and packaged files.
NSIS Abilities
3 posts
Check out NSISdl for downloading from the internet, check out contrib\NSISdl\ReadMe.txt in your NSIS directory for more information.
If you have an application or plug-in that can decrypt the files, you can call it from your installer.