Here's the original presentation back when they decompiled it: https://www.usenix.org/conference/woot13/workshop-program/pr...

And the paper: https://www.usenix.org/system/files/conference/woot13/woot13...

Basically, dropbox remapped the op codes to different values and shipped rc4 encrypted pyc files with a custom python binary that had the key inside it.