cia_extract_deckey.py

#!/usr/bin/env python3

import binascii
import struct
import sys
from Crypto.Cipher import AES

if len(sys.argv) < 3:
    print("usage: cia_extract_deckey.py <cia-file> <decrypted-titlekey>")
    sys.exit(1)

dectkey = binascii.unhexlify(sys.argv[2])

readsize = 8 * 1024 * 1024

# from http://pastebin.com/K3pVsnkq
def to_bytes(num):
    numstr = b''
    tmp = num
    while len(numstr) < 16:
        numstr += bytes([tmp & 0xFF])
        tmp >>= 8
    return numstr[::-1]

# based on http://stackoverflow.com/questions/1766535/bit-hack-round-off-to-multiple-of-8/1766566#1766566
def roundup(x):
    return (x + 63) >> 6 << 6

def showprogress(val, maxval):
    # crappy workaround I bet, but print() didn't do what I wanted
    minval = min(val, maxval)
    sys.stdout.write("\r  {:>5.1f}% {:>10} / {}".format((minval / maxval) * 100, minval, maxval))
    sys.stdout.flush()

with open(sys.argv[1], 'rb') as cia:
    # assuming the certchain and ticket never change size, which they shouldn't
    cia.seek(0x10)
    content_offset = roundup(0x2DC0 + struct.unpack("<I", cia.read(4))[0])
    cia.seek(0x2F9E)
    content_count = struct.unpack(">H", cia.read(2))[0]
    print("Content count: {}".format(content_count))
    cia.seek(0x38C4)
    chunk_records = cia.read(0x30 * content_count)
    for c in range(content_count):
        content_id = binascii.hexlify(chunk_records[(c * 0x30):(c * 0x30) + 4]).decode('utf-8')
        content_index = chunk_records[(c * 0x30) + 4:(c * 0x30) + 6]
        content_type = struct.unpack(">H", chunk_records[(c * 0x30) + 6:(c * 0x30) + 8])[0]
        content_size = struct.unpack(">Q", chunk_records[(c * 0x30) + 8:(c * 0x30) + 16])[0]
        if content_type ^ 1:
            print("Index {} with ID {} is already decrypted.".format(content_index, content_id))
            content_offset += content_size
            continue
        print("Decrypting index {}, ID {}, size {:X}".format(binascii.hexlify(content_index).decode('utf-8'), content_id, content_size))
        cia.seek(content_offset)
        cipher = AES.new(dectkey, AES.MODE_CBC, content_index + (b'\0' * 14))
        left = content_size
        with open("contents.{}.{}".format(binascii.hexlify(content_index).decode('utf-8'), content_id), 'wb') as content:
            while left > 0:
                toread = min(readsize, left)
                content.write(cipher.decrypt(cia.read(toread)))
                content_offset += toread
                left -= readsize
                showprogress(content_size - left, content_size)
            print("")