[سؤال] استفسار بخصوص دوال التشفير وفك التشفير

كود :

Public Class Security

    Public Shared trip As New System.Security.Cryptography.TripleDESCryptoServiceProvider

    Public Shared md5 As New System.Security.Cryptography.MD5CryptoServiceProvider

    Public Shared Function utf(ByVal V As String) As Byte()

        Return md5.ComputeHash(System.Text.ASCIIEncoding.UTF8.GetBytes(V))

    End Function

    Public Shared Function cod(ByVal str As String, ByVal key As String) As String

        On Error Resume Next

        trip.Key = utf(key)

        trip.Mode = System.Security.Cryptography.CipherMode.ECB

        Dim Buffer As Byte() = System.Text.ASCIIEncoding.UTF8.GetBytes(str)

        Return Convert.ToBase64String(trip.CreateEncryptor().TransformFinalBlock(Buffer, 0, Buffer.Length))

    End Function

    Public Shared Function uncod(ByVal str As String, ByVal key As String) As String

        On Error Resume Next

        trip.Key = utf(key)

        trip.Mode = System.Security.Cryptography.CipherMode.ECB

        Dim byt() As Byte = Convert.FromBase64String(str)

        Return System.Text.ASCIIEncoding.UTF8.GetString(trip.CreateDecryptor().TransformFinalBlock(byt, 0, byt.Length))

    End Function

End Class

كود :

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim a As String = Security.cod("فيجوال بيسك", "123")

        MsgBox(a)

        Dim b As String = Security.uncod(a, "123")

        MsgBox(b)

    End Sub

كود :

Imports System.IO

Imports System.Text

Imports System.Security.Cryptography



المشكلة بهذا الجزء خصوصا 

GetString(trip.CreateDecryptor().TransformFinalBlock(byt, 0, byt.Length)