Шифрование алгоритмом моноалфавитной подстановки и Алгоритмом Цезаря - VB

Формулировка задачи:

Здравствуйте, помогите исправить код чтобы выводилось одинаково зашифрованное сообщение, и методом моноалфавитной подстоновкой и методом цезаря.

Public Function MonoAlphCoder(Alph_b As String, Alph_f As String, mess As String) As String
    Dim i As Long, num As Integer, enc_mess As String
    
    For i = 1 To Len(mess)
        For num = 1 To Len(Alph_b)
            If Mid(mess, i, 1) = Mid(Alph_b, num, 1) Then
                enc_mess = enc_mess & Mid(Alph_f, num, 1)
                Exit For
            End If
        Next num
    Next i
    
    MonoAlphCoder = enc_mess
End Function
 
Public Function MonoAlphDecoder(Alph_b As String, Alph_f As String, enc_mess As String) As String
    Dim i As Long, num As Integer, dec_mess As String
    
    For i = 1 To Len(enc_mess)
        For num = 1 To Len(Alph_b)
            If Mid(enc_mess, i, 1) = Mid(Alph_f, num, 1) Then
                dec_mess = dec_mess & Mid(Alph_b, num, 1)
                Exit For
            End If
        Next num
    Next i
    
    MonoAlphDecoder = dec_mess
End Function

Public Function CaesarCoder(Alph_b As String, mess As String, ByVal key As Integer, Optional Alph_f As String) As String
    Dim i As Long, Cx As Integer, N As Integer, enc_mess As String, S As Integer
    
    N = Len(Alph_b)
    S = Sgn(key)
    'If Abs(key) > N Then key = S * (Abs(key) Mod N)
    
    For i = 0 To N
        Alph_f = Alph_f & Mid(Alph_b, (N + i + key) Mod N + 1, 1)
    Next i
    
    For i = 1 To Len(mess)
        For Cx = 0 To N - 1
            If (Mid(mess, i, 1) = Mid(Alph_b, Cx + 1, 1)) Then
                enc_mess = enc_mess & Mid(Alph_b, (N + Cx + key) Mod N + 1, 1)
                Exit For
            End If
        Next Cx
    Next i
    
    CaesarCoder = enc_mess
End Function
 
Public Function CaesarDecoder(Alph_b As String, enc_mess As String, ByVal key As Integer) As String
    Dim i As Long, Cy As Integer, N As Integer, dec_mess As String, S As Integer
    
    N = Len(Alph_b)
    S = Sgn(key)
    If Abs(key) > N Then key = S * (Abs(key) Mod N)
    
    For i = 1 To Len(enc_mess)
        For Cy = 0 To N - 1
            If (Mid(enc_mess, i, 1) = Mid(Alph_b, Cy + 1, 1)) Then
                dec_mess = dec_mess & Mid(Alph_b, (N + Cy - key) Mod N + 1, 1)
                Exit For
            End If
        Next Cy
    Next i
    
    CaesarDecoder = dec_mess
End Function

Решение задачи: «Шифрование алгоритмом моноалфавитной подстановки и Алгоритмом Цезаря»

textual
                            Листинг программы 
                        

                            Sub dfg()
MsgBox "afd"
enc1 = MonoAlphCoder("abcdefghijklmnopqrstyvwxyz", "qrstyvwxyzabcdefghijklmnop", "afd")
MsgBox enc1
dec1 = MonoAlphDecoder("abcdefghijklmnopqrstyvwxyz", "qrstyvwxyzabcdefghijklmnop", CStr(enc1))
MsgBox dec1
enc2 = CaesarCoder("abcdefghijklmnopqrstyvwxyz", "afd", 16)
MsgBox enc2
dec2 = CaesarDecoder("abcdefghijklmnopqrstyvwxyz", CStr(enc2), 16)
MsgBox dec2
End Sub
                        