Imports System.Text.Encoding
Imports System.Security.Cryptography

Namespace zaack

  Public Class SaltPasswordHashRegistry

#Region " Öffentliche Methoden "

  ''' <summary>
  ''' SaltPasswordHash erzeugen und in der Registry speichern
  ''' </summary>
  ''' <param name="pw">String</param>
  ''' <remarks> 1. öffentliche Methode (Public)</remarks>
  Public Sub CreateSaltHashAndSaveInRegistry(ByVal pw As String)
     'SaltPasswordHash erzeugen
    Dim saltPwHash As Byte() = _
     CreateSaltedPasswordHash(ASCII.GetBytes(pw), CreateSalt(2000))

     'Speichern in der Registry
    WriteToRegistry(saltPwHash)

  End Sub

  ''' <summary>
  ''' Neues Passwort mit dem aus der Registry vergleichen
  ''' </summary>
  ''' <param name="pw">String</param>
  ''' <returns>Boolean</returns>
  ''' <remarks> 2. öffentliche Methode (Public)</remarks>
  Public Function CheckNewPassword(ByVal pw As String) As Boolean
    Return VerifyPassword(ASCII.GetBytes(pw), ReadFromRegistry)
  End Function

#End Region

#Region " Registry "

  ''' <summary>
  ''' Speichern in der Registry
  ''' Application.UserAppDataRegistry
  ''' </summary>
  ''' <param name="SaltPwHash"></param>
  ''' <remarks></remarks>
  Private Sub WriteToRegistry(ByVal SaltPwHash As Byte())
    Dim name As String = "Password"
    Try
      Application.UserAppDataRegistry.SetValue(name, SaltPwHash)
    Catch ex As Exception
      MessageBox.Show(ex.Message)
    End Try
  End Sub

  ''' <summary>
  ''' Das gespeicherte SaltHashPasswort aus der Registry auslesen
  ''' </summary>
  ''' <returns>Byte()-Array oder Nothing</returns>
  ''' <remarks></remarks>
  Private Function ReadFromRegistry() As Byte()
    Dim name As String = "Password"
    Try
      If Not Application.UserAppDataRegistry.GetValue(name) _
        Is Nothing Then
        Return _
           CType(Application.UserAppDataRegistry.GetValue(name), _
           Byte())
      Else
        Return Nothing
      End If

    Catch ex As Exception
      MessageBox.Show(ex.Message)
      Return Nothing
    End Try
  End Function


#End Region

#Region " SaltPasswordHash "

  ''' <summary>
  ''' Salz bestimmter Länge erzeugen
  ''' </summary>
  ''' <param name="SaltLength">Integer</param>
  ''' <returns>Salt As Byte()</returns>
  ''' <remarks></remarks>
  Private Function CreateSalt(ByVal SaltLength As Integer) _
    As Byte()
    Dim Salt(SaltLength - 1) As Byte
     'Kryptografischer Zufallszahlen-Generator
    Dim csp As New RNGCryptoServiceProvider
    csp.GetBytes(Salt)
    Return Salt
  End Function

  ''' <summary>
  ''' Hauptfunktion:
  ''' Das gesalzene Kennwort erzeugen  (Hashwert + Salz)
  ''' </summary>
  ''' <param name="UnsaltedPassword">Kennwort als Byte()</param>
  ''' <param name="Salt">Salz-Byte()</param>
  ''' <returns>Byte()</returns>
  ''' <remarks>Kennwort als Byte()</remarks>
  Private Function CreateSaltedPasswordHash(ByVal _
    UnsaltedPassword As Byte(), ByVal Salt As Byte()) As Byte()
     ' Byte-Array-Größe bestimmen
    Dim SaltedPassword(UnsaltedPassword.Length + _
      Salt.Length - 1) As Byte
     ' Das ungesalzene Kennwort vorne einfügen
    UnsaltedPassword.CopyTo(SaltedPassword, 0)
     ' Salz annfügen
    Salt.CopyTo(SaltedPassword, UnsaltedPassword.Length)

     ' Den Hashwert für das gesalzene Kennwort erzeugen:
    Dim SaltedPasswordHash As Byte() = CreateHash(SaltedPassword)

     ' Hashwert plus Salz, Byte-Array-Größe bestimmen
    Dim SaltedPasswordHashPlusSalt(SaltedPasswordHash.Length + _
      Salt.Length - 1) As Byte
     ' Hashwert einfügen
    SaltedPasswordHash.CopyTo(SaltedPasswordHashPlusSalt, 0)
     ' Salzwert anhängen
    Salt.CopyTo(SaltedPasswordHashPlusSalt, _
      SaltedPasswordHash.Length)

     ' Gesalzenes Kennwort zurückgeben
    Return SaltedPasswordHashPlusSalt
  End Function

  ''' <summary>
  ''' Hash-Vergleich des gespeicherten mit zu prüfendem Kennwort
  ''' </summary>
  ''' <param name="UnsaltedPassword">Byte()</param>
  ''' <param name="StoredPassword">Byte()</param>
  ''' <returns>Boolean</returns>
  ''' <remarks></remarks>
  Private Function VerifyPassword(ByVal UnsaltedPassword _
    As Byte(), ByVal StoredPassword As Byte()) As Boolean
     ' Einen Hashwert vom zu prüfenden Kennwort erzeugen
    Dim UnsaltedPasswordHash As Byte() = CreateHash(New Byte() {0})
     ' Die Salt-Länge bestimmen
    Dim SaltLength As Integer = StoredPassword.Length - _
      UnsaltedPasswordHash.Length
    Dim SaltStart As Integer = StoredPassword.Length - SaltLength
    Dim Salt(SaltLength - 1) As Byte

     ' Parameter bei Nothing False
    If (UnsaltedPassword Is Nothing) OrElse _
      StoredPassword Is Nothing) Then
      Return False
    End If

     ' Salzwert ermitteln
    Dim i As Integer
    For i = 0 To SaltLength - 1
      Salt(i) = StoredPassword(SaltStart + i)
    Next
     ' Hash für das gesalzene Kennwort erzeugen
    Dim SaltedPasswordHash As Byte() = _
      CreateSaltedPasswordHash(UnsaltedPassword, Salt)
     ' Den Hash mit dem gespeicherten Wert vergleichen
    Return CompareByteArray(StoredPassword, SaltedPasswordHash)

  End Function

  ''' <summary>
  ''' Hashwert (SHA1) aus einem übergebenen Bytearray erzeugen
  ''' </summary>
  ''' <param name="ByteArrayToHash">Byte()</param>
  ''' <returns>Byte()</returns>
  ''' <remarks></remarks>
  Private Function CreateHash(ByVal ByteArrayToHash As Byte()) _
    As Byte()
    Dim sha As SHA1 = SHA1.Create()
    Return sha.ComputeHash(ByteArrayToHash)

  End Function

  ''' <summary>
  ''' Byte-Arrays vergleichen
  ''' </summary>
  ''' <param name="bArr1">Byte()</param>
  ''' <param name="bArr2">Byte()</param>
  ''' <returns>Boolean</returns>
  ''' <remarks></remarks>
  Private Function CompareByteArray(ByVal bArr1 As Byte(), _
    ByVal bArr2 As Byte()) As Boolean
     ' Gleiche Länge?
    If (bArr1.Length <> bArr2.Length) Then
      Return False
    End If
     ' Iterieren und einzelne Arrayelemente vergleichen
    Dim i As Integer
    For i = 0 To bArr1.Length - 1
      If bArr1(i) <> bArr2(i) Then
        Return False
      End If
    Next

    Return True
  End Function

#End Region

  End Class

End Namespace