urgent help needed if possible

I use the following function to encrypt data and save it to the registry

VB Code:

Public Function EncryptPassword(strPass As String) As String
  Dim XOR_String As String
  Dim i As Integer
  
  For i = 1 To Len(strPass)
    XOR_String = XOR_String & Chr(Asc(Mid(strPass, i, 1)) Xor ((i * 5) Mod 256))
  Next i
  
  EncryptPassword = XOR_String
End Function

I know it is not secure, but the point was not to secure the data, just to really not make it readable and deter a user from editing the values themselves...

anyway our product has a CD key that is validated in the app using a simple algorithm. A problem was realized when a customer was able to activate with the key but then the internal function that validates it failed. Long story short, i found out that the encryption function produces odd results when certain characters are in certain locations in the string

XXXX-XXXX-7XXX-XXXX
XXXX-XXXX-XXAX-XXXX
XXXX-XXXX-XXXF-XXXX
XXXX-XXXX-XXXX-PXXX
XXXX-XXXX-XXXX-XUXX
XXXX-XXXX-XXXX-XXZX

I found this out by writing a quick program that encrypted and then decrypted each possible value and compaired it to the original string. So when the above keys have the certain char in a certain position this error occurs. I think the conversion may make it a carrage return or some unreadable character which is causing the error....

any ideas?

To test this out... pass "XXXX-XXXX-XXXF-XXXX" to the function to encrypt it and then decrypt it and compare to the original string.. it is cut off at the bad character...

further testing indicates that it is producing a character 0 for some of the encrypted values which is of course null which would explain the problem...

perhaps this function is just no good to use....

i found if i change the multiplication factor of the xor value to 2 instead of 5 it does not produce any bad keys.. going to test it with all values to see if it will work though

VB Code:

Public Function EncryptPassword(strPass As String) As String
  Dim XOR_String As String
  Dim i As Integer
  For i = 1 To Len(strPass)
    XOR_String = XOR_String & Chr(Asc(Mid(strPass, i, 1)) Xor ((i * 2) Mod 256))
  Next i
  
  EncryptPassword = XOR_String
End Function

You know they put people away for talking to themselves right?

Concur. Any value higher than 2 produces decimal values less than 33 (outside the range of a valid Ascii character)

This line (in the For Next) demonstrates it well:

Debug.Print Asc(Mid(strPass, i, 1)) Xor ((i * 5) Mod 256)




Bruce.

BrainS thanks for nothing

Bruce, yeah I found that it will work fine changing it to 2 except the problem will still be present when using longer strings. Do you know of any way I can modify the function to only work with valid ASCII characters?

Moding with 16 seems to work with the limited testing I did.

Actually 32 seems to be fine aswell.

Xor ((i * 5) Mod 32)

I have no solution to it sorry...but have you seen the basic encryption example at Lucky's???


Havn't looked at it my self. But I remember I saw it here...

http://rookscape.com/vbgaming/encrypt.zip

Quote:

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Originally posted by Bruce Fox
Actually 32 seems to be fine aswell.

Xor ((i * 5) Mod 32)

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thanks, I was able to modify the function and fix the problem (i hope ):D

Not in a good mood? Learn to take a joke once in awhile, you'll live longer.

Quote:

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Originally posted by kleinma
BrainS thanks for nothing

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Quote:

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Originally posted by BrianS
Not in a good mood? Learn to take a joke once in awhile, you'll live longer.

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When someone posts a request for urgent help and all you can do is drop a lame joke, it is annoying. I am all for fun, but just not in a situation like this where I need to find a fix for software that is being used by customers... sorry

Not sure if you still need this but lf you do then look at this sample by Randy Birch.