Imports System.Security.Cryptography
Imports System.Text

Public Class ClassPasswordCrypto

    Private _password As String

    ' ++++++++++++++++++++++++++++++++++++++++++++++ Properties ++++++++++++++++++++++++++++++++++++++++++++++

    ''' <summary>
    ''' Liefert das Passwort zum Entschlüsseln des Lizenzschlüssels
    ''' </summary>
    ''' <value></value>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public ReadOnly Property Password() As String
        Get
            Return Me._password
        End Get
    End Property

    ' ++++++++++++++++++++++++++++++++++++++++++++++ Methoden ++++++++++++++++++++++++++++++++++++++++++++++

    ''' <summary>
    ''' Konstruktor für den Lizenz-Manager ohne License load
    ''' </summary>
    ''' <param name="password">Passwort zum Entschlüsseln des Lizenzkeys</param>
    ''' <remarks></remarks>
    Sub New(ByVal password As String)
        Me._password = password
    End Sub

    ''' <summary>
    ''' Codiert eine Zeichenkette
    ''' </summary>
    ''' <param name="str">zu verschlüsselnde Zeichenkette</param>
    ''' <param name="password">das zur Verschlüsselung verwendete Passwort</param>
    ''' <returns>liefert eine verschlüsselte Zeichenkette</returns>
    ''' <remarks></remarks>
    Public Function EncodePassword(ByVal str As String, ByVal password As String)
        Dim rd As New RijndaelManaged

        Dim md5 As New MD5CryptoServiceProvider
        Dim key() As Byte = md5.ComputeHash(Encoding.UTF8.GetBytes(password))

        md5.Clear()
        rd.Key = key
        rd.GenerateIV()

        Dim iv() As Byte = rd.IV
        Dim ms As New IO.MemoryStream

        ms.Write(iv, 0, iv.Length)

        Dim cs As New CryptoStream(ms, rd.CreateEncryptor, CryptoStreamMode.Write)
        Dim data() As Byte = System.Text.Encoding.UTF8.GetBytes(str)

        cs.Write(data, 0, data.Length)
        cs.FlushFinalBlock()

        Dim encdata() As Byte = ms.ToArray()
        Dim result As String = Convert.ToBase64String(encdata)
        cs.Close()
        rd.Clear()

        Return result
    End Function

    ''' <summary>
    ''' Decodiert den verschlüsselten Lizenzkey
    ''' </summary>
    ''' <param name="licenseCodeStr">verschlüsselter Lizenzkey</param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Function DecodePassword(ByVal licenseCodeStr As String)
        Try
            Dim rd As New RijndaelManaged
            Dim rijndaelIvLength As Integer = 16
            Dim md5 As New MD5CryptoServiceProvider
            Dim key() As Byte = md5.ComputeHash(Encoding.UTF8.GetBytes(Me._password))

            md5.Clear()

            Dim encdata() As Byte
            Dim ms
            Dim iv(15) As Byte
            Dim cs As CryptoStream
            Dim data() As Byte

            Try
                encdata = Convert.FromBase64String(licenseCodeStr)
                ms = New IO.MemoryStream(encdata)

                ms.Read(iv, 0, rijndaelIvLength)
                rd.IV = iv
                rd.Key = key

                cs = New CryptoStream(ms, rd.CreateDecryptor, CryptoStreamMode.Read)

                ReDim data(ms.Length - rijndaelIvLength)
            Catch ex As Exception
                Return Nothing
            End Try

            Dim i As Integer = 0

            Try

                i = cs.Read(data, 0, data.Length)
                Dim result As String = System.Text.Encoding.UTF8.GetString(data, 0, i)

                cs.Close()
                rd.Clear()
                Return result

            Catch ex As Exception

                'MsgBox("Falsches Passwort")
                Return Nothing

            End Try
        Catch ex As Exception
        End Try
        'MsgBox("Falsches Passwort")
        Return Nothing
    End Function

End Class