2old.py

'''
2old by zoogie
convert new3ds exclusives to old3ds titles (maybe)

run this on an extracted and decrypted main cxi
then rebuild the cia with:
makerom -f cia -o game.cia -target t -i 0.cxi:0:0
you might need to use an older makerom as the newer ones tend to throw a -10 error
don't take this too seriously, most likely the games that work on old3ds are simplistic and sucky XD
'''
import hashlib, os, sys
buff=""
replace=""
smdh=0
exefs=0
SMDH=-1
MB=1024*1024
MAX_READ=32*MB


f=open(sys.argv[1],"rb+")
#print(hashlib.sha256(test).digest())

def bytes2int(data):
    u32=(ord(data[0])*1)+(ord(data[1])*0x100)+(ord(data[2])*0x10000)+(ord(data[3])*0x1000000)
    return u32

def patchByte(f, offset, data):
    f.seek(offset)
    f.write(data)

def updateSHA256(f, hash_offset, data_offset, length):
    data=""
    hash=""
    f.seek(data_offset)
    data=f.read(length)
    hash=hashlib.sha256(data).digest()
    f.seek(hash_offset)
    f.write(hash)

def findSMDH(f):
    global exefs
    global smdh

    f.seek(0x1A0)
    bytes=f.read(4)
    exefs=bytes2int(bytes) * 0x200

    f.seek(exefs+0x28)
    bytes=f.read(4)
    smdh=bytes2int(bytes) + 0x200

    f.seek(exefs + smdh)
    bytes=f.read(4)
    if bytes != "SMDH":
        return -1

    return exefs + smdh

SMDH=findSMDH(f)
print(hex(smdh))

f.seek(SMDH+0x2029)
buff=f.read(1)
buff=chr(ord(buff) & 0xEF)
f.seek(SMDH+0x2029)
f.write(buff)

updateSHA256(f, exefs+0x1A0, SMDH, 0x36c0)
updateSHA256(f, 0x1C0, exefs, 0x200)

f.seek(0x40E)
buff=f.read(1)
buff=chr(ord(buff) | 0x30)
patchByte(f,0x40E,buff)

updateSHA256(f, 0x160, 0x200, 0x400)

f.seek(0x80E)
buff=f.read(1)
buff=chr(ord(buff) | 0x30)
patchByte(f,0x80E,buff)

patchByte(f, 0x150, "C")
#patchByte(f, 0x10B, "\x00")
#patchByte(f, 0x11B, "\x00")

print(hex(SMDH))
f.close()