Option Explizit

----------------------------
Private Sub cmdEntschlüsseln_Click()
 Dim UnverText As String, VerText, temp As String
 Dim Schlüssel, i As Integer
 Dim Länge, temp2 As Long
  
VerText = txtVerschlüsselt
 
 Schlüssel = txtSchlüssel
 
Länge = Len(VerText)

For i = 1 To Länge
    temp = Mid(VerText, i, 1)
    temp2 = Asc(temp)
    temp2 = temp2 - Schlüssel
        If temp2 < 32 Then
           temp2 = 255 - Schlüssel
        End If
    temp = Chr(temp2)
    UnverText = UnverText & temp
Next i

 txtUnverschlüsselt = UnverText
 txtVerschlüsselt = ""
 
End Sub

----------------------------
Private Sub cmdVerschlüsseln_Click()
 Dim UnverText As String, VerText, temp As String
 Dim Schlüssel, i As Integer
 Dim Länge, temp2 As Long
  
UnverText = txtUnverschlüsselt
 
 Schlüssel = txtSchlüssel
 
Länge = Len(UnverText)

For i = 1 To Länge
    temp = Mid(UnverText, i, 1)
    temp2 = Asc(temp)
    temp2 = temp2 + Schlüssel
        If temp2 > 255 Then
           temp2 = 32 + Schlüssel
        End If
    temp = Chr(temp2)
    VerText = VerText & temp
Next i

 txtVerschlüsselt = VerText
 txtUnverschlüsselt = ""
 
End Sub