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Find out what accesses... crash - sometimes.

 
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ulysse31
Master Cheater
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Joined: 19 Mar 2015
Posts: 324
Location: Paris

PostPosted: Wed Aug 05, 2015 4:24 pm    Post subject: Find out what accesses... crash - sometimes. Reply with quote

Hi fellow cheaters.

I am trying to find the packet encryption function of an online game.
To this end I have found the ID of a skill before it is encrypted and the same ID after it is encrypted, I got the post encryption ID by wireshark.

I have started to narrow down the encryption function although i am still dealing with tens of thousands of code lines and I encounter one problem :

I found the code which pushes the skill ID and doing so determines the skill packet that will be sent, I tried to find out what accesses the stack adress where the skill value is stored, I can see the first few codes reading it but it always crashs right after i start finding out what accesses a stack address.

So I am wondering if there is a reason for that and if there is a way around it.
Thanks !
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Zanzer
I post too much
Reputation: 126

Joined: 09 Jun 2013
Posts: 3278

PostPosted: Wed Aug 05, 2015 4:42 pm    Post subject: Reply with quote

Edit > Settings > Debugger Options > Debugger method > Use VEH Debugger
?
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ulysse31
Master Cheater
Reputation: 2

Joined: 19 Mar 2015
Posts: 324
Location: Paris

PostPosted: Wed Aug 05, 2015 4:54 pm    Post subject: Reply with quote

Yep Already done, the windows debugger crashs instantly the game.

I can find out what accesses on most variable, just crashes when it's a stack variable (I think it's related to the fact it's being accessed a lot by many codes then but not sure)
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deama1234
Master Cheater
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Joined: 20 Dec 2014
Posts: 328

PostPosted: Wed Aug 05, 2015 6:46 pm    Post subject: Reply with quote

Have you tried other debuggers? Like the windows debugger or kernelmode.

With the VEH debugger, try ticking all the options under "Debugger interface config".

Try playing with the "Size of stack to record..."
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ulysse31
Master Cheater
Reputation: 2

Joined: 19 Mar 2015
Posts: 324
Location: Paris

PostPosted: Thu Aug 06, 2015 1:24 am    Post subject: Reply with quote

Thank you for taking interest into my issue.

Yes I have tried other debuggers, as a matter of fact this game is protected by themida Tiger and Fish latest version and only CE VEH or CE kernel on my 32 bit are able to stealthly debug this game and they both crash when finding out what accesses a stack variable.

A few months back i was able to use a script and some tweakings to unpack this game and successfully attach ollyDBG but the script is no longer up to date with Themida.
And the game even detects Oly with strongOG, phantom plugin and ScyllaHide plugin.
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ulysse31
Master Cheater
Reputation: 2

Joined: 19 Mar 2015
Posts: 324
Location: Paris

PostPosted: Fri Aug 07, 2015 3:06 am    Post subject: Reply with quote

Okay so while I don't havea proof, It seems pretty clear by now that the tracing slows a given thread that much that it loses a synchronisation with other stuff going on.
It happens to crash whenever a certain area of code is entered, the way around this if anyone happens to stumble upon the same issue is to set a conditionnal lua breakpoint based on the EIP.

Such a great tool this Cheat Engine, thank you master Dark Byte.

Ps : Found the decryption function.
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