It's quite simple, for anyone trying to extract a level.
The first four bytes are the size of the level file, including these four bytes themself but excluding everything past the last level file.
After this, each level file is stored one by one. The first four bytes of a level file is the size of the file, minus 32.
Immediately after the last level, is the name of the level pack, followed by 00.
The next two bytes are the number of levels in the pack.
Everything from there on is the adress within the file at which each level file is found.
Quite a simple one, so extracting levels is very easy. It's not encrypted in any way.
