Шифрование строки смещением

Option Explicit
Option Compare Text
Const AlfaBet As String = "абвгдеёжзийклмнопрстухцчшщъыьэюя" & _
                          "abcdefghijklmnopqrstuvwxyz" & _
                          "1234567890"
                          
Sub Command1_Click()
  Dim i As Long, sIn As String, sOut As String
  Dim s1 As String, s2 As String, s3 As String
    sIn = InputBox("Введите строку", "Ввод данных", "1234567890")
    s1 = ChangeLetters(sIn)
    s2 = CaesarCoder(AlfaBet, s1, 7)     ' cмещение - 7
    s3 = CaesarDecoder(AlfaBet, s2, 7)
    sOut = ChangeLetters(s3)
    MsgBox "Введённая строка:   " & sIn & vbCrLf & _
           "Строка с заменой мест:   " & s1 & vbCrLf & _
           "Кодированная смещением:   " & s2 & vbCrLf & _
           "Декодированная строка:   " & s3 & vbCrLf & _
           "Восстановленная строка:   " & sOut
End Sub
 
Function ChangeLetters(ByVal S As String) As String
    Dim st As String, i As Long
    For i = 1 To Len(S) Step 2
              st = st & Mid(S, i + 1, 1) & Mid(S, i, 1)
    Next i
    ChangeLetters = st
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)
    
    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

Option Explicit
 
Function rep(S As String) As String
Dim b() As Byte
Dim bb As Byte
Dim i As Long
b = S
For i = 0 To UBound(b) - 2 Step 4
  bb = b(i)
  b(i) = b(i + 2)
  b(i + 2) = bb
Next i
rep = b
End Function
 
Function Shift(S As String, n As Integer) As String
Dim b() As Byte
Dim i As Long
b = S
For i = 0 To UBound(b) Step 2
  b(i) = (n + b(i)) And 255
Next i
Shift = b
End Function
 
Sub Example()
Dim S As String
'шифруем
S = "ШиФр"
S = rep(S)
S = Shift(S, 15)
MsgBox S
'дешифруем
S = Shift(S, -15)
S = rep(S)
MsgBox S
End Sub