Nintendo File Formats

AC:NH > Save Data

This page is based on Animal Crossing: New Horizons version 3.0.0.

AC:NH uses a system wide save data archive, instead of one save data archive per user. The following files can be found in the save data archive:

• landname.dat
• main.dat
• mainHeader.dat

In addition, up to 8 folders named Villager0 up to Villager7 may be present. These contain the following files:

• personal.dat
• personalHeader.dat
• photo_studio_island.dat
• photo_studio_islandHeader.dat
• postbox.dat
• postboxHeader.dat
• profile.dat
• profileHeader.dat

Everything is stored in little-endian byte order.

Header Files

All files, except for landname.dat, are encrypted with AES-CTR. The header file, that is stored along with each file, contains information that is used to generate the key and IV:

The key and IV are generated using the SEAD RNG, as follows:

def generate_data(seed: int, skips: int) -> bytes:
    rng = Random(seed)
    for i in range(skips):
        rng.u64()
    
    data = []
    for i in range(16):
        data.append(rng.u32() >> 24)
    return bytes(data)

def generate_key(table: list[int]) -> bytes:
    seed = table[table[0] & 0x7F]
    skips = (table[table[1] & 0x7F] & 0xF) + 1
    return generate_data(seed, skips)

def generate_iv(table: list[int]) -> bytes:
    seed = table[table[2] & 0x7F]
    skips = (table[table[3] & 0x7F] & 0xF) + 1
    return generate_data(seed, skips)

The rest of this page describes the format of decrypted save data files.

landname.dat

main.dat

Sources

Besides reverse engineering, the following sources were used for this page:

• https://gist.github.com/Treeki/d46ac2f8cd9111f60f48b6707207fa4a