Re: Slow down string changers

From: Gerhard W. Gruber (sparhawk_at_gmx.at)
Date: 01/28/04 

Date: Wed, 28 Jan 2004 22:21:03 +0100

On Wed, 28 Jan 2004 04:30:21 +0100 wrote "The Half A Wannabee"
<ShakainZulu_AT(dimmu borgir - fear and wonder)_Hotmail.com> in alt.lang.asm
with <40172dbc$1@news.broadpark.no>

>> I can think of a couple of ways.
>> I don't want to encrypt the string.
>>
>> a. Do a CRC of the string and check it against a stored value
>> b. Check the string at a few locations for certain characters
>> c. Do (a) and if it fails write the correct string in the .exe
>>
>> Thanks.
>
>c. And where would the correcting string be stored ?

Also you have the problem that, if the protection code and the exectuable is
the same file, then its a bit hard to write to the file while it is running.
:) Depending on the OS of course. Under plain DOS this is no problem, but
under Windows this shouldn't work and I think also not under Linux.

Another thing to take care of. If you use a CRC for protection then you can
easily calculate a correcting value which will result in the same CRC but with
different data. This means that the data you check shouldn't contain any
padbytes, otherwise they can be used to correct the CRC. For a CRC32 you would
need 4 padbytes to do this. 

-- 
Gerhard Gruber
Maintainer of
SoftICE for Linux - http://pice.sourceforge.net/
Fast application launcher - http://sourceforge.net/projects/launchmenu

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