Imports System.IO
Imports System.Security.Cryptography
Imports System.Text
 
Public Class Form1
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        Try
            Dim filename As String = "test.docx"
 
            Dim fs As New FileStream(filename, FileMode.Open)
            Dim br As New BinaryReader(fs)
 
            Dim b(CInt(br.BaseStream.Length)) As Byte
 
            br.Read(b, 0, b.Length)
            br.Close()
 
            WriteFile(b, "crypted.docx_x")
 
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button2.Click
        Try
            Dim filename = "decrypted.docx"
            Dim fs As New FileStream(filename, FileMode.Create)
 
            Dim s = ReadFile("crypted.docx_x")
            Dim b(CInt(s.Length - 1)) As Byte
 
            s.Position = 0
            s.Read(b, 0, b.Length)
 
            fs.Write(b, 0, b.Length)
 
            fs.Close()
 
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
 
    Private spwd As String = "123456789011"
 
    Public Function WriteFile(ByVal b As Byte(), ByVal filename As String) As _
      Boolean
        Dim fs As FileStream = New FileStream(filename, FileMode.Create, _
        FileAccess.Write)
 
        Try
            Dim rd As New RijndaelManaged
            Dim md5 As New MD5CryptoServiceProvider
            Dim bkey() As Byte = Encoding.Default.GetBytes(spwd)
            Dim key() As Byte = md5.ComputeHash(bkey)
 
            md5.Clear()
            rd.Key = key
            rd.IV = key
            rd.Padding = PaddingMode.ANSIX923
 
            Dim cryptostream As New CryptoStream(fs, rd.CreateEncryptor, _
              CryptoStreamMode.Write)
 
            cryptostream.Write(b, 0, b.Length - 1)
            cryptostream.FlushFinalBlock()
 
            fs.Close()
 
            Return True
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
 
        Return False
    End Function
 
    Public Function ReadFile(ByVal filename As String) As Stream
        If Not IO.File.Exists(filename) Then
            Throw New IOException("File not found! (" + filename + ")")
        End If
 
        Dim ms As New MemoryStream
        Dim fs As New FileStream(filename, FileMode.Open, FileAccess.Read)
        Try
            Dim rd As New RijndaelManaged
            Dim md5 As New MD5CryptoServiceProvider
            Dim key() As Byte = md5.ComputeHash(Encoding.UTF8.GetBytes(spwd))
            md5.Clear()
            rd.Key = key
            rd.IV = key
            rd.Padding = PaddingMode.None
 
            Dim cryptostream As New CryptoStream(fs, rd.CreateDecryptor, _
              CryptoStreamMode.Read)
            Dim b(CInt(fs.Length - 1)) As Byte
 
            cryptostream.Read(b, 0, b.Length)
            ms.Write(b, 0, b.Length)
 
            fs.Close()
 
            Return ms
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
 
        Return Nothing
    End Function
 
End Class

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