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Savage, posted Thu Oct 01, 2015 9:45 pm (7878)

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Hi! i tried this script

http://aluigi.altervista.org/bms/arcsys.bms

But looks is not working well this new game i get no errors, just it can't decompress the file

Here is an example
http://www90.zippyshare.com/v/GLmwfEqu/file.html (4,86 Mb's)

Thanks!

aluigi, posted Thu Oct 01, 2015 9:51 pm (7879)

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That file you provided seems all encrypted.

P.S. there was no need to paste the script in the post

Savage, posted Thu Oct 01, 2015 11:55 pm (7881)

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aluigi wrote:

That file you provided seems all encrypted.

All the pac files are like the example

aluigi wrote:

P.S. there was no need to paste the script in the post

Oki doki

Ekey, posted Fri Oct 02, 2015 1:06 am (7884)

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Encryption: Hash mt19937 (Mersenne Twister) Xor. It works like this:

1) Extract file name from full path
2) Convert file name to uppercase
3) Create hash from file name (simple algorithm > see below)

Code:

   unsigned int dwSeed = 137;
   unsigned int dwHash = 0;
   for(int i = 0; i    {
      dwHash = (dwHash * dwSeed)   (*iFileName);
   }

4) Initialize mt from hash
5) Decrypt data (simple algorithm > see below)

Code:

   fseek(fi, 0, SEEK_END);
   size_t dwSize = ftell(fi);
   fseek(fi, 0, SEEK_SET);
   
   ;malloc, read, etc.
   
   mt_init_genrand(dwHash);
   do
      *(DWORD *)(pBuffer   4 * i  ) ^= mt_genrand_int32();
   while (i 

Easy 

aluigi, posted Fri Oct 02, 2015 2:41 am (7886)

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I have made a script that can be reused all the times that it's used mersenne twist:
http://aluigi.org/bms/arcana_heart_3.bms

I have also verified the generated values of mt_genrand_int32 with both the script and the C file and they are correct.
The decrypted file is ok but I don't know if it's a mistake that the archived filenames look "strange".

Ekey, posted Fri Oct 02, 2015 10:18 am (7893)

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Hm... Yes something wrong. First DWORD after decrypt must be 0x46504143 (FPAC)

aluigi, posted Fri Oct 02, 2015 10:34 am (7894)

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Maybe there constants at the end of mt_genrand_int32 are custom? 0x9d2c5680 and 0xefc60000
The script is 1:1 with the C function, so there are no other ideas.
Have you verified everything with a C tool or that's just the result of the debug analysis?

Ekey, posted Fri Oct 02, 2015 10:42 am (7895)

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Nope, it's my fault. Here correct one.

Code:

set XSEED "0x43415046"
for i = 0 < SIZE
    callfunction mt_genrand_int32 1
    get TMP long
    math TMP ^ y
    math XSEED ^ TMP
    put XSEED long MEMORY_FILE
next i

aluigi, posted Fri Oct 02, 2015 10:47 am (7896)

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Well done. Script updated to version 0.1.1

Savage, posted Sat Oct 03, 2015 11:16 am (7920)

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Amazing!!, works great

Thanks!!

Mysticus, posted Fri Apr 30, 2021 7:53 am (63663)

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I know this topic is now 5 years old.
But it looks like they made a new way to crypt .pac files from the latest update called SIXSTARS!!!!!! XTEND.
All I get is this linked below.
I uncrypted with the AH3 decryption .bms file, but the result is the same.
Any update for the script?

aluigi, posted Wed May 12, 2021 10:38 am (63928)

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PAC is still encrypted (maybe it uses a different method/key) while PK3 looks like just data without any index.

Mysticus, posted Wed May 12, 2021 2:13 pm (63945)

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aluigi wrote:

PAC is still encrypted (maybe it uses a different method/key) while PK3 looks like just data without any index.

Do you plan to update your script to match these different encryption?

aluigi, posted Wed May 12, 2021 3:31 pm (63949)

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Give me the new encryption scheme and key and I will do it.
Obviously I can't guess them from nowhere.

Ekey, posted Thu May 13, 2021 2:29 pm (64005)

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Unfortunately, I do not have this game, so I can't help you too.

@Mysticus
Edited: I checked the script and it works fine with files from SIXSTARS!!!!!! XTEND. File you provided has the wrong name > https://steamdb.info/depot/661991/
Correct path and filename is >

Code:

SteamData/data/ahdata/act/chara/chara_split_00.pac

So, filename must be chara_split_00.pac instead chara_split_00_unpacked.pac

Therefore, the file can't be decrypted, because generated hash from filename is invalid. I renamed chara_split_00_unpacked.pac to chara_split_00.pac and it was perfectly decrypted.

If you want to decrypt files from this game then don't rename them

Mysticus, posted Fri May 14, 2021 6:37 pm (64046)

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@Ekey
I tried with the correct path and file name. But I still get "unpacked" file name.
What can I do?

PurpleFlow , posted Tue Jul 06, 2021 12:17 am (65061)

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Hello, I just started decrypting one of the game files and ran into a problem.

Code:

SteamData\data\ahdata\sound\bgm\bgm01_op03.pac

I try using the script on the file in this location but the program decrypts the file as a pac file instead turning into an audio file. Am I doing something wrong or is it supposed to return as a pac file?