Awesome
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 |