A compression/decompresson script (with optional GUI) that allows user to compress/decompress Nintendo Switch ROMs loselessly, thanks to zstd compression algorithm. The compressed file can be installed directly with supported NSW Homebrew Title Installers.
How to install:
There are several ways the install the script. You can find details on installation for all of them below.
You need to have a hactool compatible keys file in a suitable directory to use the script.
The keys file must be located as prod.keys file in %USERPROFILE%/.switch/(Windows)/$HOME/.switch/(UNIX) or keys.txt in the working directory.
It can be dumped with Lockpick_RCM.
NSZ files are not a real format, they are functionally identical to NSP files. Their sole purpose to alert the user that it contains compressed NCZ files. NCZ files can be mixed with NCA files in the same container.
NSC_Builder supports compressing NSP to NSZ, and decompressing NSZ to NSP. The sample scripts located here are just examples of how the format works.
XCZ files are not a real format, they are functionally identical to XCI files. Their sole purpose to alert the user that it contains compressed NCZ files. NCZ files can be mixed with NCA files in the same container.
These are compressed NCA files. The NCA's are decrypted, and then compressed using zStandard. Only NCA's with a 0x4000 byte header are supported (CNMT nca's are not supported).
The first 0x4000 bytes of a NCZ file is exactly the same as the original NCA (and still encrypted).
At 0x4000, there is the variable sized NCZ Header. It contains a list of sections which tell the decompressor how to re-encrypt the NCA data after decompression. It can also contain an optional block compression header allowing random read access.
All of the information in the header can be derived from the original NCA + Ticket, however it is provided preparsed to make decompression as easy as possible for third parties.
Directly after the NCZ header, the zStandard stream begins and ends at EOF. The stream is decompressed to offset 0x4000. If block compression is used the stream is splatted into independent blocks and can be decompressed as shown in https://github.com/nicoboss/nsz/blob/master/nsz/BlockDecompressorReader.py
class Section: def __init__(self, f): self.magic = f.read(8) # b'NCZSECTN' self.offset = f.readInt64() self.size = f.readInt64() self.cryptoType = f.readInt64() f.readInt64() # padding self.cryptoKey = f.read(16) self.cryptoCounter = f.read(16) class Block: def __init__(self, f): self.magic = f.read(8) # b'NCZBLOCK' self.version = f.readInt8() self.type = f.readInt8() self.unused = f.readInt8() self.blockSizeExponent = f.readInt8() self.numberOfBlocks = f.readInt32() self.decompressedSize = f.readInt64() self.compressedBlockSizeList =  for i in range(self.numberOfBlocks): self.compressedBlockSizeList.append(f.readInt32()) nspf.seek(0x4000) sectionCount = nspf.readInt64() for i in range(sectionCount): sections.append(Section(nspf)) if blockCompression: BlockHeader = Block(nspf)
Requires latest hactool compatible prod.keys at
Windows: %userprofile%.switch\ (enter .switch. as foldername to get a folder named .switch)
or keys.txt at the location of nsz.py/nsz.exe
Please dump your keys using Lockpick_RCM
Always keep your keys up to date as otherwise newer games can't be decrypted anymore.
nsz --level 18 -C title1.nsp title2.nsp title3.nsp
will generate title1.nsz title2.nsz title3.nsz
This tool was only tested with base games, updates and DLCs.
nsz.py --help usage: nsz.py [-h] [-C] [-D] [-l LEVEL] [-B] [-s BS] [-V] [-p] [-t THREADS] [-o OUTPUT] [-w] [-r] [-i INFO] [--depth DEPTH] [-x EXTRACT [EXTRACT ...]] [-c CREATE] [--rm-source] [file [file ...]] positional arguments: file optional arguments: -h, --help show this help message and exit -C Compress NSP -D Decompress NSZ -l LEVEL, --level LEVEL Compression Level -B, --block Uses highly multithreaded block compression with random read access allowing compressed games to be played without decompression in the future however this comes with a low compression ratio cost. Current title installers do not support this yet. -s BS, --bs BS Block Size for random read access 2^x while x between 14 and 32. Default is 20 => 1 MB. Current title installers do not support this yet. -V, --verify Verifies files after compression raising an unhandled exception on hash mismatch and verify existing NSP and NSZ files when given as parameter -p, --parseCnmt Extract TitleId/Version from Cnmt if this information cannot be obtained from the filename. Required for skipping/overwriting existing files and --rm-old- version to work properly if some not every file is named properly. Supported filenames: *TitleID*[vVersion]* -t THREADS, --threads THREADS Number of threads to compress with. Numbers < 1 corresponds to the number of logical CPU cores. -o OUTPUT, --output OUTPUT Directory to save the output NSZ files -w, --overwrite Continues even if there already is a file with the same name or title id inside the output directory -r, --rm-old-version Removes older version if found -i INFO, --info INFO Show info about title or file --depth DEPTH Max depth for file info and extraction -x EXTRACT [EXTRACT ...], --extract EXTRACT [EXTRACT ...] extract / unpack a NSP -c CREATE, --create CREATE create / pack a NSP --rm-source Deletes source file/s after compressing/decompressing. It's recommended to only use this in combination with --verify
SciresM for his hardware crypto functions; the blazing install speeds (50 MB/sec +) achieved here would not be possible without this.
Que novedades incluye la versión 4.0.1
Replaced PyInstaller with WinPython for the portable Windows release.
- I spent a lot of time deleting every piece of the python standard library not required to run nsz in order to save storage and speed up extraction time by having less files to extract.
- This was done because PyInstaller triggered false positive detections on Windows Defender as reported in #82
- Tested on Windows 7, Windows 10 and Windows Server 2019
This version ONLY affects the portable Windows release. The PIP release wasn't updated as only the deployment of the Portable windows build is affected by this change.