Xor on string--help me please

**gaya3_k** · November 3rd, 2009, 11:56 PM

hi,
in my program i am Xor ing 3 strings , i am taking each character in the strings and Xor ing their ASCII values
but manually if i do Xor operation i am getting a different answer,
Can someone tell me how this result is coming,
x="7CA674" first string
lenx=len(x)

y="17767F" Second string
leny=len(y)

z="251270" Third string
lenz=len(z)

and my code is

For l = 1 To Len(x)

l Mid$(x, l, 1) = (Asc(Mid$(x, l, 1)) Xor Asc(Mid$(y,leny , 1)) Xor Asc(Mid$(z, lenz, 1)))

Next l
and my result is
x = 376456

**gaya3_k** · November 4th, 2009, 12:00 AM

hi,
in my program i am Xor ing 3 strings , i am taking each character in the strings and Xor ing their ASCII values
but manually if i do Xor operation i am getting a different answer,
Can someone tell me how this result is coming,
x="7CA674" first string
lenx=len(x)

y="17767F" Second string
leny=len(y)

z="251270" Third string
lenz=len(z)

and my code is

Originally Posted by gaya3_k

For l = 1 To Len(x)

l Mid$(x, l, 1) = (Asc(Mid$(x, l, 1)) Xor Asc(Mid$(y,leny , 1)) Xor Asc(Mid$(z, lenz, 1)))

Next l

and my result is
x = 376456

**dglienna** · November 4th, 2009, 03:48 PM

Bitwise operations can only be executed on BYTE data types. You'd have to convert.

CBYTE() might help

**gaya3_k** · November 4th, 2009, 09:52 PM

Thanks alot for your reply,

Can u please tell me exactly what CBYTE will do to solve my problem.

Gayathri.k

**dglienna** · November 5th, 2009, 01:25 AM

Each character is has a byte code. You can't use a part of a character, unless you convert it to a byte

Take a look at this link:
http://msdn.microsoft.com/en-us/libr...8VS.80%29.aspx

**WoF** · November 5th, 2009, 04:26 AM

No, no.
You can xor integers as well as ASC values.
The problem is in the expression

Code:

 Mid$(x, l, 1) = (Asc(Mid$(x, l, 1)) Xor Asc(Mid$(y,leny , 1)) Xor Asc(Mid$(z, lenz, 1)))

Look what you are doing: from the y string and the z string you are always taking only ever the last character.
Make it so:

Code:

 Mid$(x, l, 1) = (Asc(Mid$(x, l, 1)) Xor Asc(Mid$(y,l , 1)) Xor Asc(Mid$(z, l, 1)))

l is the loop variable which increments with every step in the for loop. leny and lenz are constantly pointing the last character of y and z.

**gaya3_k** · November 6th, 2009, 01:32 AM

thanks alot for your reply,
my exact code is

Code:

Private Sub XORIt(ByRef data As String, ByRef key As String, ByRef Y As String)
    Dim l As Long
    Dim lonLenKey As Long, lonKeyPos, lonLenTime, lonTmePos As Long
    Dim key_file As String
    key_file = "input\key.txt"
    
    lonLenKey = Len(key)
    
    For l = 1 To Len(data)
    
        lonKeyPos = lonKeyPos + 1
               If lonKeyPos > lonLenKey Then lonKeyPos = 1
        Mid$(data, l, 1) = (Asc(Mid$(data, l, 1)) Xor Asc(Mid$(key, lonKeyPos, 1)))
          
    Next l
    
    lonLenTime = Len(Y)
    For l = 1 To Len(data)
    
       
        lonTmePos = lonTmePos + 1
        If lonTmePos > lonLenTime Then lonKeyPos = 1
        Mid$(data, l, 1) = (Asc(Mid$(data, l, 1)) Xor Asc(Mid$(Y, lonTmePos, 1)))
          
    Next l
    
      
    
    Close #55
     Open key_file For Output As #55
     Print #55, Hex(data)
     Close #55
    
    
End Sub

what i am doing is ,each time my key,data and time will be different values taken from a text file as a string.
say for example,
data value is "7CA674"
key is "17767FA"
time is "25127000"

i will take the length of each string and i will do the xor operation, till the length of least string

my result for these value is 376456
Please someone justify this answer.

I am not getting how this result is coming

Thanks in advance,
Gayathri.K

**WoF** · November 6th, 2009, 11:19 AM

No, I'm getting a different result. Let me show you how I did it:

Code:

Private Sub XORTest()
'data Value Is "7CA674"
'key is "17767FA"
'time is "25127000"
'result is 376456

  Dim dat$, key$, tim$ 'the strings
  Dim ld&#37;, lk%, lt%, lm1%, lmin% 'being the lengths and minimum
  Dim i%, res$
  
  dat = "7CA674"
  key = "17767FA"
  tim = "25127000"
  
  ld = Len(dat)
  lk = Len(key)
  lt = Len(tim)
  
  'get the minimum in 2 steps for better overview
  lm1 = IIf(ld < lk, ld, lk)
  lmin = IIf(lt < lm1, lt, lm1)
  'lmin is now the shortest length
  
  For i = 1 To lmin
    res = res + Chr$(Asc(Mid$(dat, i, 1)) Xor Asc(Mid$(key, i, 1)) Xor Asc(Mid$(tim, i, 1)))
  Next
  MsgBox res
    
End Sub

The result is "4AG27B". I'm quite confident of the result.
I get the min length of all three strings, then in a loop I xor the ASC values of corresponding characters in same positions and add the Chr$() of the resultin value to the resulting string res$.
I'm confident, because I use a similar algorithm to xor strings for simple encoding.

Let me hint, that you are making a common error.

Code:

   Dim lonLenKey As Long, lonKeyPos, lonLenTime, lonTmePos As Long

lonKeyPos and lonLenTime wont be long. You have to declare As Long for every variable individually. Without it, it becomaes a variant.
If lazy for writing, you can use the shortcuts
Dim a&, b&, c&, d$, i%
a, b, and c become Long, d becomes string and i% will be integer.

Also you don't need longs for this. Integer is sufficient.