Imports System.Security.Cryptography
Imports System.IO
Imports System.Text
 
Public Class Form1
    Inherits System.Windows.Forms.Form
 
#Region " Windows Form Designer generated code "
 
    ' Generated from "pw" aber so etwas wie "rTz16p??x79" wäre besser...
    Private _pwhash As Byte() = {&H1A, &H91, &HD6, &H2F, &H7C, &HA6, &H73, _
      &H99, &H62, &H5A, &H43, &H68, &HA6, &HAB, &H5D, &H4A, &H3B, &HAA, &H60, _
      &H73}
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        PasswordTextBox.Text = "pw"
        WriteDataTextBox.Text = "some data" + vbCrLf + "more data"
    End Sub
 
    Private Sub GenerateHashButton_Click(ByVal sender As System.Object, ByVal e _
      As System.EventArgs) Handles GenerateHashButton.Click
        Dim h As New SHA1Managed
 
        Dim hash As Byte() = h.ComputeHash(Encoding.UTF8.GetBytes( _
          PasswordTextBox.Text))
        h.Clear()
        hx(hash)
    End Sub
 
    Private Sub WriteDataButton_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles WriteDataButton.Click
        Dim fs As New FileStream("C:\enc.txt", FileMode.Create, _
        FileAccess.Write, FileShare.None)
 
        Dim rm As New RijndaelManaged
 
        rm.GenerateIV()
        Dim iv() As Byte = rm.IV
 
        SetRijndaelKey(rm, _pwhash)
 
        fs.Write(iv, 0, iv.Length)
 
        Dim cs As New CryptoStream(fs, rm.CreateEncryptor(), _
          CryptoStreamMode.Write)
 
        Dim sw As New StreamWriter(cs, Encoding.UTF8)
        sw.Write(WriteDataTextBox.Text)
        sw.Close()
        rm.Clear()
 
    End Sub
 
    Private Sub ReadDataButton_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles ReadDataButton.Click
 
        If Not checkPassword(PasswordTextBox.Text) Then
            MsgBox("Password invalid")
            Return
        End If
 
        Dim fs As New FileStream("C:\enc.txt", FileMode.Open, FileAccess.Read, _
          FileShare.None)
 
        Dim rm As New RijndaelManaged
 
        Dim iv(rm.IV.Length - 1) As Byte
 
        fs.Read(iv, 0, iv.Length)
 
        rm.IV = iv
 
        SetRijndaelKey(rm, _pwhash)
 
        Dim cs As New CryptoStream(fs, rm.CreateDecryptor(), _
          CryptoStreamMode.Read)
 
        Dim sr As New StreamReader(cs, Encoding.UTF8)
        ReadDataTextBox.Text = sr.ReadToEnd()
        sr.Close()
        rm.Clear()
 
    End Sub
 
    Private Function checkPassword(ByVal pw As String) As Boolean
        Dim h As New SHA1Managed
 
        Dim hash As Byte() = h.ComputeHash(Encoding.UTF8.GetBytes( _
          PasswordTextBox.Text))
        h.Clear()
        For i As Integer = 0 To hash.Length - 1
            If _pwhash(i) <> hash(i) Then Return False
        Next
        Return True
    End Function
 
    Private Sub SetRijndaelKey(ByVal rm As Rijndael, ByVal seed As Byte())
        Dim key(rm.KeySize / 8 - 1) As Byte
 
        Dim j As Integer
 
        For i As Integer = 0 To key.Length - 1
            If j = seed.Length Then j = 0
            key(i) = seed(j)
            j += 1
        Next
        rm.Key = key
    End Sub
 
    Private Sub hx(ByVal ba() As Byte)
        For Each b As Byte In ba
            Debug.Write(Hex(b))
        Next
        Debug.WriteLine("")
    End Sub
 
End Class