5 Replies - 1288 Views - Last Post: 15 September 2012 - 08:26 PM

#1 troncolo  Icon User is offline

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Reverse engineer Checksum?

Posted 15 September 2012 - 07:53 PM

I have a .crc file with the following text:


CheckSum=4d696c1343332


How could you reverse engineer this, and change it?
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#2 troncolo  Icon User is offline

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Re: Reverse engineer Checksum?

Posted 15 September 2012 - 08:12 PM

Sorry, Ok, I have a MACH-O file and a crc file. There are other data files and when I try to edit them, It gives me an error whenever I run the program, So I'm trying to get rid of the checksum so I can edit freely.

(The other files are .json files)
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#3 blackcompe  Icon User is offline

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Re: Reverse engineer Checksum?

Posted 15 September 2012 - 08:15 PM

The most important property of a hash function (i.e. checksum) is that it's one-way, meaning you can't go from the output to the input. So the answer is: you can't.
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#4 troncolo  Icon User is offline

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Re: Reverse engineer Checksum?

Posted 15 September 2012 - 08:19 PM

I found something in the MACH-O file that looks like it relates to the crc:

_get_crctable


Ok, So there is no possible way to do this?

What if you removed everything relating to the checksum?
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#5 GunnerInc  Icon User is online

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Re: Reverse engineer Checksum?

Posted 15 September 2012 - 08:25 PM

Please explain what you are trying to do. CRCs are usually a part of executable files (and other files) so you know if they have been modified by someone/something. By you wanting to bypass them, does not sound kosher.
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#6 blackcompe  Icon User is offline

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Re: Reverse engineer Checksum?

Posted 15 September 2012 - 08:26 PM

Quote

Ok, So there is no possible way to do this?


I have no idea what you're trying to do, but you absolutely can't reverse a checksum (at least not a cryptographic one). Maybe you should ask about MACH-O files on a Mac forum.

This post has been edited by blackcompe: 15 September 2012 - 08:27 PM

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