Enkripsi Kriptografi Vernam

Public Class Form1
    Private Sub BtnEnkripsi_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnEnkripsi.Click
        Dim j As Integer
        Dim jum As Integer
        Dim skey As String
        Dim nkata As Integer
        Dim nkunci As Integer
        Dim sKata As String
        Dim sPlain As String = ""
        Dim nEnc As Integer
        j = 0
        skata = Plainteks.Text
        jum = Len(skata)
        skey = Kunci.Text
        For i = 1 To jum
            If j = Len(skey) Then
                j = 1
            Else
                j = j + 1
            End If
            nKata = Asc(Mid(skata, i, 1)) - 65
            nkunci = Asc(Mid(skey, j, 1)) - 65
            nEnc = ((nkata + nkunci) Mod 26)
            sPlain = sPlain & Chr((nEnc) + 65)
        Next i
        Chiperteks.Text = sPlain

    End Sub

    Private Sub Plainteks_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles Plainteks.KeyPress
        e.KeyChar = UCase(e.KeyChar)
        Dim Tombol As Integer = Asc(e.KeyChar)
        If Not (((Tombol >= 65) And (Tombol <= 90)) Or (Tombol = 8)) Then
            e.Handled = True
        End If
    End Sub

    Private Sub Kunci_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles Kunci.KeyPress
        e.KeyChar = UCase(e.KeyChar)
        Dim tombol As Integer = Asc(e.KeyChar)
        If Not (((tombol >= 65) And (tombol <= 90)) Or (tombol = 8)) Then
            e.Handled = True
        End If
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Plainteks.Text = ""
        Kunci.Text = ""
        Chiperteks.Text = ""
    End Sub

End Class