A little script I ported from C that will recalculate hashes of Super Mario Galaxy save files (GameData.bin).

checksum_galaxy.py

# 6/26/16
# A little script I ported from C that will recalculate hashes of Super Mario
# Galaxy save files (GameData.bin). Thanks to MasterF0x and Mathew_Wi (Matt)
# for the original C script. Thanks to Marionumber1 for putting the checksum
# algorithm on the wiibrew wiki, where they found it
# (http://wiibrew.org/wiki/Super_Mario_Galaxy_savefile). Thanks to Treeki/Ninji
# for reverse-engineering the algorithm in the first place.
# Running with no arguments will cause it to scan for all .bin files in the
# same folder as itself (non-recursively) and fix all of their hashes.
# Running with one or more arguments will cause it to fix the hash of the
# file(s) given.

# Licensed under the MIT License:

# Copyright (c) 2016 RoadrunnerWMC

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

import sys


def generate_checksum(data):
    c1 = c2 = 0
    for i in range(0, len(data), 2):
        val = data[i] << 8 | data[i+1]
        c1 = (c1 + val) & 0xFFFF
        c2 = (c2 + ~val) & 0xFFFF

    return (c1 << 16) | c2


def fixSavegame(data):
    checksum = generate_checksum(data[4:])
    data = bytearray(data)
    data[0] = checksum >> 24
    data[1] = (checksum >> 16) & 0xFF
    data[2] = (checksum >> 8) & 0xFF
    data[3] = checksum & 0xFF
    return bytes(data)


def main(argv):
    if len(argv) > 1:
        print('Fixing the files passed as arguments:')
        for file in argv[1:]:
            print('Fixing ' + file)
            with open(file, 'rb') as f:
                data = f.read()
            with open(file, 'wb') as f:
                f.write(fixSavegame(data))
    else:
        print('Fixing all .bin files in this folder:')
        for fn in os.listdir('.'):
            if not fn.endswith('.bin'): continue

            print('Fixing ' + file)
            with open(fn, 'rb') as f:
                data = f.read()
            with open(fn, 'wb') as f:
                f.write(fixSavegame(data))


if __name__ == '__main__': main(sys.argv)