Private Sub Command1_Click()
   Dim v As String
 
   v = Crypt("code", "Geheimwort")
   v = Decrypt("code", "ISKIKAZSTH")
End Sub
 
Private Function Crypt(s, g) As String
   Dim c As Integer
   Dim x As Integer
   Dim y As Integer
   Dim z As Integer
 
   y = -1
   s = UCase(s)
   g = UCase(g)
 
   For x = 1 To Len(g)
      y = (y + 1) Mod Len(s)
      z = Asc(Mid(g, x, 1)) - 64
      c = (z + Asc(Mid(s, y + 1, 1)) - 65) Mod 26
      If c = 0 Then c = 26
      Crypt = Crypt & Chr(c + 64)
   Next x
End Function
 
Private Function Decrypt(s, g) As String
   Dim c As Integer
   Dim x As Integer
   Dim y As Integer
   Dim z As Integer
 
   y = -1
   s = UCase(s)
   g = UCase(g)
 
   For x = 1 To Len(g)
      y = (y + 1) Mod Len(s)
      z = Asc(Mid(g, x, 1)) - 64
      c = (z - Asc(Mid(s, y + 1, 1)) - 65) Mod 26
      Decrypt = Decrypt & Chr(c + 90)
   Next x
End Function