LZSS compressed files in Pokemon Battle Revolution

[Poryhack]

I was hoping to examine some files in Pokemon Battle Revolution (PBR), but most of the files are compressed in a way that I have not been able to decompress with any of the standard Nintendo schemes (both variants of LZ77, RL, and Huffman). Each compressed file begins with "LZSS" so I believe it would be a safe to assume that it uses a variant of that compression scheme.

I have made a couple basic observations, but I don't think I'd be able to puzzle out how to decompress these files on my own, hence this topic.

• In traditional GBA/NDS/Wii compressed files there is a 4-byte header, the first byte of which specifies a compression method and the last 3 which give an decompressed filesize. The header in this case is preceded by "LZSS".
• The compression method byte on these files is left blank (00).
• The decompressed filesize seems to be big-endian.

You can download a sample file here. As many more as you need are available on request.

I'd be incredibly grateful to anyone who figures this out.

[aluigi]

yes it looks just lzss (although I'm not 100% sure) with the only difference that the initial value of the sliding window doesn't seem to be the classical "space" char but a null one.
the following quickbms script does the job:

Code: Select all

endian big
comtype lzss "12 4 2 2 0"
idstring LZSS
get SIZE long
get ZSIZE long
get DUMMY long
savepos OFFSET
math ZSIZE -= OFFSET

get NAME filename
string NAME += ".unpacked"
clog NAME OFFSET ZSIZE SIZE