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GPinzone

Doing a XOR on a MD5

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I needed to perform an XOR on two MD5 hashes. The problem is that a MD5 will overflow an integer, so AutoIT treats it as a string. I came up with a function to handle this, but I'm sure that it's not as efficient as it could be.

Here's what I came up with:

#include <Crypt.au3>

Func md5($message)
Return _Crypt_HashData($message, $CALG_MD5)
EndFunc ;==>md5

Func _BitXOR_Hex($h1, $h2)
If StringLeft($h1, 2) = "0x" Then $h1 = StringMid($h1, 3)
If StringIsXDigit($h1) = 0 Then
SetError(1)
MsgBox(0, "Error", "Wrong input, try again ...")
Return ""
EndIf

If StringLeft($h2, 2) = "0x" Then $h2 = StringMid($h2, 3)
If StringIsXDigit($h2) = 0 Then
SetError(1)
MsgBox(0, "Error", "Wrong input, try again ...")
Return ""
EndIf

; Add leading zeros to smaller hex string if different length.
If StringLen($h1) > StringLen($h2) Then
For $i = 1 To StringLen($h1) - StringLen($h2)
$h2 = "0" & $h2
Next
ElseIf StringLen($h2) > StringLen($h1) Then
For $i = 1 To StringLen($h2) - StringLen($h1)
$h1 = "0" & $h1
Next
EndIf

Local $result = "0x"
For $i = 1 To StringLen($h1)
Local $t1 = "0x" & StringMid($h1, $i, 1)
Local $t2 = "0x" & StringMid($h2, $i, 1)
Local $t3 = StringMid($HX_REF, BitXOR($t1, $t2) + 1, 1)
$result = $result & $t3
Next

Return $result
EndFunc ;==>_BitXOR_Hex

It basically operates a BitXOR on each hex digit at a time.


Gerard J. Pinzonegpinzone AT yahoo.com

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