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[JAVA] How to calculate the cheksum?

Started by Reipers, February 16, 2013, 06:39:18 PM

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Reipers

February 16, 2013, 06:39:18 PM Last Edit: February 16, 2013, 08:45:02 PM by Lenophis
Hello people! My name is Reinaldo, translate mobile games some years ago here in Brazil. I am currently translating a game called Heroes Lore Zero. It has a folder that contains all items in the game so far could not figure out how to translate these items. I'm with the game in 3 versions: English, Russian and Chinese. Comparing the files, it was found that there is protection through CHECKSUM. In each version there is a checksum that is different in each of the versions. My question is: How to calculate the checksum? The low, see one of the files I'm trying to translate.

Spoiler
[close]

Look in each version the check digit.
English: 8B
Russian: 2A
Chinese: 8C
If anyone knows how to calculate the checksum, please help me. Only that I lack to complete the translation of Heroes Lore Zero to portuguese.

--Moderator edit--
Fixed formatting errors.

Bisqwit

#1
March 12, 2013, 02:48:52 PM
Your best bet is probably try to trace the ROM code and see how it verifies the sum. Just put a breakpoint at reading the memory address of the checksum, and trace backwards and forwards a bit to see how the variables that the checksum is compared to are calculated.

henke37

#2
March 12, 2013, 03:19:50 PM
Looks like it is small enough to brute force. Anyway, it is likely a literal sum if it is just 8 bits.

Bisqwit

#3
March 12, 2013, 03:29:09 PM
Likely is not good enough. I already tried that, and it does not match.

FinS

#4
March 12, 2013, 04:20:42 PM
Looks like it's just the checksum 8 of the first byte before the item up to the checksum. This also applies to the other items so that is confirmative.

Bisqwit

#5
March 14, 2013, 09:13:10 AM
Quote from: FinS on March 12, 2013, 04:20:42 PMLooks like it's just the checksum 8 of the first byte before the item up to the checksum. This also applies to the other items so that is confirmative.

Ah, nice. I only tried the parts that the original posted had highlighted. Good catch.

Ridculle

#6
March 14, 2013, 09:20:51 AM
Quote from: FinS on March 12, 2013, 04:20:42 PM
Looks like it's just the checksum 8 of the first byte before the item up to the checksum. This also applies to the other items so that is confirmative.



By the way, what is your hex editor?
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