Public Function XOREncryption(strCodeKey As String, _
    strDataIn As String) As String

Dim lonDataPtr As Long
Dim intXORValue1 As Integer
Dim intXORValue2 As Integer
Dim strDataOut As String

For lonDataPtr = 1 To Len(strDataIn)
    ' The first value to XOR comes from the data to be
    ' encrypted.
    intXORValue1 = Asc(Mid$(strDataIn, lonDataPtr, 1))
    ' The second value to XOR comes from the code key.
    intXORValue2 = Asc(Mid$(strCodeKey, _
        ((lonDataPtr Mod Len(strCodeKey)) + 1), 1))
    ' The two values are XORed together to create a
    ' decrypted character.
    strDataOut = strDataOut + Chr(intXORValue1 Xor _
        intXORValue2)
Next lonDataPtr

' The XOREncryption function returns the encrypted (or
' decrypted) data.
XOREncryption = strDataOut

End Function
To try out the XOREncryption routine, you can add it to a form that has three TextBox controls (Text1, Text2, and Text3) and a CommandButton control. In the CommandButton's Click event, add the following code:
Dim strCodeKey As String
Dim strEncryptedText As String

strCodeKey = "Wxz19hgl3Kb2dSp"
strEncryptedText = XOREncryption(strCodeKey, Text1.Text)
Text2.Text = strEncryptedText
Text3.Text = XOREncryption(strCodeKey, strEncryptedText)