Print Page - Calculating checksum value

Title: Calculating checksum value
Post by: Vortex on January 15, 2005, 02:39:12 PM

Here is an algo to calculate the MS checksum value of a PE, it was presented by f0dder at Harold's forum:


MicrosoftCheckSum2 PROC C uses esi, buf:dword, len:dword
	mov ecx, [len]           
	mov edx, [buf]           
	shr  ecx, 1               
	xor  eax, eax             
	clc                                  
@@theLoop:
	adc ax, [edx + (ecx * 2) - 2]
	dec ecx
	jnz @@theLoop
	adc eax, [len]
	ret
MicrosoftCheckSum2 ENDP

Title: Re: Calculating checksum value
Post by: Mirno on January 15, 2005, 05:45:03 PM

That code?
I originally wrote that on Hiro's original forum!

BTW the clc isn't needed, the XOR does it.

Mirno

Title: Re: Calculating checksum value
Post by: Vortex on January 16, 2005, 09:44:46 AM

Hi Mirno,

Yes, I checked it, you are right.

Kindly, please accept my apologies.

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General Forums => The Laboratory => Topic started by: Vortex on January 15, 2005, 02:39:12 PM