Add support for StuffIt X encryption

[ci-macpaw]

Originally reported on Google Code with ID 723

mikerich88:

I have a sitx file that was created several years ago, which contains a Mac OS 9 System
Folder. Stuffit Expander does successfully extract the contents.

The Archive Browser says "File is not fully supported", and shows an empty archive.

lsar detects that it is a Stuffit X archive, but then prints "Archive parsing failed!
(File is not fully supported.)" and exits.

It is not encrypted at all, and was probably created using DropStuff 7.0.3 on Mac OS
9. So it seems like that at least the contents should be able to be listed, even if
not every file may be extracted.

The file has been posted at http://www.mikerichardson.name/SystemFolder.sitx (73 MB),
please let me know when it has been downloaded so I can delete it from the server.

[ci-macpaw]

paracelsus:

No, those are stored elsewhere. It wouldn't surprise me if it just means it has some
encryption added to it with a derived password just to make it harder to understand
the format, though. This is already done for uncompressed files, they are encrypted
with a simple password, just to mask the contents.

[ci-macpaw]

mikerich88:

How is it encrypted though? That's very odd, I just extracted the file again, using
Stuffit Expander 11.0.2 (Intel) on Mac OS X 10.9.5, and I did not have to enter any
password.

Maybe "encryption algorithm 2" is some kind of flag that indicates a compressed directory/file
listing? The archive has over 2000 files.

[ci-macpaw]

paracelsus:

It does seem to be encrypted after all, it reports it's using encryption algorithm 2.

[ci-macpaw]

paracelsus:

Got it, will look into it later.