vb.net加密解密方法

1.vb.net加密解密方法

Private Function getLicenseDate() As String
            Dim b() As Byte
            Dim path As String = Server.MapPath(Context.Request.ApplicationPath) & "License\"
            Try
                If Not System.IO.Directory.Exists(path) Then
                    System.IO.Directory.CreateDirectory(path)
                End If
            Catch ex As IO.IOException
                Page.ClientScript.RegisterStartupScript(Me.GetType(), "Alert", "<script>alert('对不起，你可能没有创建文件夹的权限')</script>")
                Exit Function
            End Try
            Dim output As String
            Dim filePath As String = path & "License.dat"
            If File.Exists(filePath) Then
                Try
                    Dim fs As New FileStream(filePath, FileMode.Open)
                    Dim sr As New StreamReader(fs)
                    output = sr.ReadToEnd().ToString()
                    sr.Close()
                    fs.Close()
                    'output = Convert.ToBase64String(System.Text.Encoding.Default.GetBytes(filePath))
                Catch ex As Exception
                    Page.ClientScript.RegisterStartupScript(Me.GetType(), "Alert", "<script>alert('读取LIENCE文件异常！请取消勾选License文件夹下的License.dat的只读属性！')</script>")
                End Try
            Else
                Exit Function
            End If
            Try
                b = Convert.FromBase64String(output)
            Catch ex As Exception
                Page.ClientScript.RegisterStartupScript(Me.GetType(), "Alert", "<script>alert('对不起,,发生错误')</script>")
            End Try
            Try
                output = System.Text.Encoding.GetEncoding(-).GetString(b)
                Dim startIndex As Integer = output.IndexOf("<ValidityDate>") + "<ValidityDate>".Length
                Dim endIndex As Integer = output.IndexOf("</ValidityDate>")
                Dim index As Integer = endIndex - startIndex
                If startIndex >  And endIndex >  And index >  Then
                    output = output.Substring(startIndex, index)
                Else
                    output = "-1"
                End If
            Catch ex As Exception
                Page.ClientScript.RegisterStartupScript(Me.GetType(), "Alert", "<script>alert('获取License信息发生异常')</script>")
                output = ""
            End Try
            Return output

        End Function

2. viewstate 作用域是本页面