Ok I did it
Version 0.3 supporting both ar03 and ar04 completely, added keys for Superposition and Oil Rush, added a couple of new options and features like the possibility of scanning a text file searching for the right key (both plain-text and unigine-archived key [base64+zlib]):http://aluigi.org/papers/uniginex.zip
It's a command-line tool but it should work by "dragging" the ung archive over uniginex.exe (but will close immediately in case of errors or when it terminates).
It's not necessary to specify the output folder but it's highly suggested:
uniginex.exe c:\PATH\superposition.ung c:\output_folder