Imports System.IO
Imports System.Security.Cryptography
Imports System.Text

Public Class Form1

    Public Shared Function DecryptTripleDES(ByVal sOut As String, ByVal sKey As String) As String
        Dim provider As New TripleDESCryptoServiceProvider
        Dim provider2 As New MD5CryptoServiceProvider
        sKey = Form1.ScrambleKey(sKey)
        provider.Key = provider2.ComputeHash(Encoding.ASCII.GetBytes(sKey))
        provider.Mode = CipherMode.ECB
        Dim transform As ICryptoTransform = provider.CreateDecryptor
        Dim inputBuffer As Byte() = Convert.FromBase64String(sOut)
        Return Encoding.ASCII.GetString(transform.TransformFinalBlock(inputBuffer, 0, inputBuffer.Length))
    End Function

    Private Shared Function ScrambleKey(ByVal v_strKey As String) As String
        Dim builder As New StringBuilder
        Dim length As Integer = v_strKey.Length
        Dim i As Integer = 1
        Do While (i <= length)
            Dim start As Integer = ((v_strKey.Length - i) + 1)
            builder.Append(Strings.Mid(v_strKey, start, 1))
            i += 1
        Loop
        Dim str2 As String = builder.ToString
        Return builder.ToString
    End Function

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox3.Text = DecryptTripleDES(TextBox1.Text, TextBox2.Text)
    End Sub
End Class