Decode-Encode

'Öncelikle Form İçerisine Yerleştirmemiz Gereken Nesneleri 
'Yazayım.

'txtNormal(Textbox)
'txtSifreli(Textbox)
'cmd_Sifrele(Command Button)
'cmd_Çöz(Command Button)

'Gelelim Kodlara...

Private Sub cmd_Çöz_Click()
Dim Enc, Dec, TEnc, Org As String
txtNormal = txtSifreli
txtSifreli = ""
Dim ttllen, dtime As Integer
txtSifreli.Text = ""
Org = txtNormal.Text
ttllen = Len(txtNormal.Text)
    For i = 1 To ttllen

        Dec = Mid(Org, i, 1)
        Dec = Asc(Dec)
        Dec = ((Dec - 10) + 5)
        Dec = Chr(Dec)
        Dec = Asc(Dec)
        Dec = ((Dec - 10) + 2)
        Dec = Chr(Dec)

        TEnc = TEnc & Dec
            Next i

txtSifreli.Text = TEnc

End Sub
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Private Sub cmd_Sifrele_Click()

Dim Enc, Dec, TEnc, Org As String

Dim ttllen As Integer

ttllen = Len(txtNormal.Text)

txtSifreli.Text = ""

Org = txtNormal.Text
    For i = 1 To ttllen
        Enc = Mid(Org, i, 1)
        Enc = Asc(Enc)
        Enc = ((Enc + 10) - 5)
        Enc = Chr(Enc)
        Enc = Asc(Enc)
        Enc = ((Enc + 10) - 2)
        Enc = Chr(Enc)
        TEnc = TEnc & Enc

    Next i

txtSifreli.Text = TEnc

End Sub