ROM Hack Need Help with CRC check

Raphland

New Member
OP
Newbie
Joined
Sep 9, 2006
Messages
3
Trophies
0
XP
36
Country
Canada
Im trying to edit a save file. I have located where the crc is, and on what data it is applied.

It is a 32 bit crc, but im not sure how it is generated. I tried with the standard crc 32 and it does not generate the right crc.

If anyone is good enough to figure this out, please teach me how to do it.

The crc is at offset 0x000001F8 to 0x000001FB
The data it checks is from offeset 0x000001FC to 0x000003F3

Here is the file in question (file):

(41 52 44 53 30 30 30 30 30 30 30 30 30 30 30 31 43 00 6F 00 6E 00 74 00 72 00 61 00 20 00 34 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 31 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 43 6F 6E 74 72 61 20 34 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 2F 00 00 00 01 31 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 45 54 43 59 AB CB 5B 27 01 00 00 00 00 00 00 00 AE 48 04 00 00 00 00 00 04 04 01 00 00 00 00 00 34 00 00 00 03 01 04 01 FF FF FF FF FF 02 00 FF FF FF FF FF 01 00 FF 0F 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00)
 

FAST6191

Techromancer
Editorial Team
Joined
Nov 21, 2005
Messages
36,798
Trophies
3
XP
28,284
Country
United Kingdom
Without examining it in depth CRC is probably the wrong word (stuff like FF3 uses bytesums although it can reach md5 grade stuff).

Tracing can be a bit hard with freeware stuff right now but you could simply make a trainer like crackers FF3 one that circumvents the save (I am afraid I have not been following the codes for contra so that may also not be an option).

As for CRCs can I suggest HxD, it is a nice freeware editor with some custom CRC capabilities:
http://mh-nexus.de/hxd/

Oh and I would suggest hacking RAW saves rather than AR stuff.
 

Raphland

New Member
OP
Newbie
Joined
Sep 9, 2006
Messages
3
Trophies
0
XP
36
Country
Canada
Allright thank you, finally an answer.

I will make sure to look into the bytesum and MD5 algorithms.

As for Hxd, thats what Im already using. I played quite a bit with its custom CRC option but did not get very far. I tried all the 32 bit CRC polynomials on http://en.wikipedia.org/wiki/Cyclic_redundancy_check with all the possible settings.

Hacking the AR files or raw files does not really make a different. The only difference is the AR files have extra data at the beginning, which I conveniently ignore.
 

Site & Scene News

Popular threads in this forum

General chit-chat
Help Users
    K3Nv2 @ K3Nv2: Pump the chocolate into my veins