`nand` - NAND images

The nand module enables reading and writing of Nintendo 3DS NAND images.

A basic overview of reading and writing to a NAND image is available here: Example: Read and write NAND partitions.

Getting started

Here’s a quick example to get inside CTRNAND and read files from within it using PyFatBytesIOFS:

from pyctr.type.nand import NAND
from pyfatfs.PyFatFS import PyFatBytesIOFS

with NAND('nand.bin') as nand:
    with PyFatBytesIOFS(fp=nand.open_ctr_partition()) as ctrfat:
        with ctrfat.open('/private/movable.sed', 'rb') as msed:
            msed.read()

A second example trying to load SecureInfo. This one is tricky because some consoles use SecureInfo_A and some use SecureInfo_B, so we have to try both.

from pyctr.type.nand import NAND
from pyfatfs.PyFatFS import PyFatBytesIOFS
from fs.errors import ResourceNotFound

with NAND('nand.bin') as nand:
    with PyFatBytesIOFS(fp=nand.open_ctr_partition()) as ctrfat:
        for l in 'AB':
            path = '/rw/sys/SecureInfo_' + l
            if ctrfat.exists(path):
                with ctrfat.open(path, 'rb') as f:
                    f.read()
                    break

Required files

In most cases users will have a NAND backup with an essentials backup embedded. However there are plenty of cases where this may not occur, so you may need to provide support files in other ways.

The only hard requirement is an OTP. This is found in the essentials backup, but otherwise can be provided as a file, file-like object, and a bytestring.

NAND CID is also useful to have but is not required for most consoles. This also is loaded from the essentials backup if found, otherwise it can be provided like OTP. If it’s not found anywhere, PyCTR will attempt to generate the Counter for both CTR and TWL. The Counter for TWL will not be generated if the TWL MBR is corrupt.

In either case the load priority is first file, then bytestring, then essentials backup.

An external essential.exefs file must manually be loaded with ExeFSReader and then the individual otp and nand_cid read and provided to the NAND initializer.

Dealing with corruption

There are cases where the NAND is corrupt but you still want to read it.

One of the most common kinds of corruption is an invalid TWL MBR. This happens if the NCSD header is replaced with one of another console. This applies mostly to very old pre-sighax NAND backups. If the TWL MBR cannot be decrypted and parsed, but a NAND CID was loaded, PyCTR will use the default partition information. Otherwise, TWL information will be inaccessible.

NAND objects

NAND sections

class pyctr.type.nand.NANDSection

This defines the location of partitions in a NAND.

All the enums here are negative numbers to refer to different types of partitions rather than physical locations when used with NAND.open_raw_section(), because while 99% of users will never alter the partitions, it is still possible to do so and this module will handle those use cases.

Special sections

These are not actual sections of the NAND/NCSD but are included for convenience.

Exceptions

Custom NCSD interaction

These are for those who want to manually interact with the NCSD information.

class pyctr.type.nand.NCSDPartitionInfo

Information for a single partition.

fs_type: PartitionFSType | int: Type of filesystem.

encryption_type: PartitionEncryptionType | int: Type of encryption used for the partition.

offset: int: Offset of the partition in bytes.

size: int: Size of the partition in bytes.

nand - NAND images