nsZip

Work in progress file format for compressed Nintendo Switch games and a tool to compress/decompress them.

Please note that nsZip currently only supports the depreciated NSZP but not the new homebrew compatible NSZ file format so I highly recommend to use https://github.com/nicoboss/nsz instead.

NSZ file format:

Header:

Offset	Size	Description
0x00	0x05	XOR-Encrypted magic ("nsZip")
0x05	0x05	Random key to decrypt the magic
0x0A	0x01	Version (for now 0x00)
0x0B	0x01	nsZip Type

Type 0:

Offset	Size	Description
0x0C	0x01	Compression algorithm
0x0D	File size - 0x1D	Full compressed file
File size - 0x10	0x10 (first half)	SHA256 of everything above

Type 1:

Offset	Size	Description
0x0C	0x05	bs = Decompressed Block Size
0x11	0x04	Amount of Blocks
0x15 + x * y	0x01	Compression algorithm
0x16 + x * y	y - 1	cbs = Compressed Block Size
0x15 + (x+1) * y	sum(cbs)	Concatenated compressed blocks
File size - 0x10	0x10 (first half)	SHA256 header XOR SHA256 compressed

y = ceil(log2(bs)/8) + 1

Note: The compressed block isn't allowed to be larger than the decompressed data - please use compression algorithm 0x00 (None) in that case or cbs might overflow!

Type 2:

Offset	Size	Description
0x0C	0x04	Amount of Blocks
0x10	0x01	s = Size of size parameters
0x11 + x * y	0x01	Compression algorithm
0x12 + x * y	s	bs = Decompressed Block Size
0x12 + x * y + s	s	cbs = Compressed Block Size
0x12 + (x+1) * y	sum(cbs)	Concatenated compressed blocks
File size - 0x10	0x10 (first half)	SHA256 header XOR SHA256 compressed

y = 2 * s + 1

Compression algorithms:

Value	Algorithm	Recommended Parameters
0x00	None	None - Just use memcpy
0x01	Zstandard	CompressionLevel = 19
0x02	lzma	Dic=1536, WordS=273, cLevel=9