Imports System.Security.Cryptography

        '文字列の暗号化、復号化を行うクラス
        Public Class Crypto

            'キー
            Private mKey As Byte()
            '初期化ベクタ
            Private mIV As Byte()

            '暗号化キー
            Public Property Key() As Byte()
                Get
                    Return mKey
                End Get
                Set(ByVal Value As Byte())
                    mKey = Value
                End Set
            End Property

            '初期ベクタ
            Public Property IV() As Byte()
                Get
                    Return mIV
                End Get
                Set(ByVal Value As Byte())
                    mIV = Value
                End Set
            End Property


            '文字列の暗号化
    Public Function Encrypt(ByVal value As String,Byval size as Integer) As Byte()
        Debug.Assert(Not (mKey Is Nothing))
        Debug.Assert(Not (mIV Is Nothing))
        Try
            If value.Trim = "" Then
                Return Nothing
            End If

            Dim byteArray(size) As Byte
            Dim ms As New IO.MemoryStream(byteArray)
            'Dim ms As New IO.MemoryStream()
            Dim rm As New RijndaelManaged
            Dim cs As New CryptoStream(ms, rm.CreateEncryptor(mKey, mIV), _
                                        CryptoStreamMode.Write)
            Dim sw As New IO.StreamWriter(cs)

            'ストリームに書き出し
            sw.WriteLine(value)

            '書き込まれたバッファを読み込み
            'byteArray = ms.GetBuffer

             sw.Close()
             cs.Close()

             Return byteArray

        Catch ex As IndexOutOfRangeException
            Throw New InvalidOperationException("Keyは8バイト、IVは16バイトの指定が必要です")
        Catch ex As Exception
            Throw ex
        End Try

    End Function


    'バイトデータを復号化
    Public Function Decrypt(ByVal value As Byte()) As String
        Debug.Assert(Not (mKey Is Nothing))
        Debug.Assert(Not (mIV Is Nothing))

        '何もデータがないときは空欄を返す
        If value Is Nothing Then
            Return ""
        End If

        Dim ms As New IO.MemoryStream(value)
        Dim rm As New RijndaelManaged
        Dim cs As New CryptoStream(ms, rm.CreateDecryptor(mKey, mIV), CryptoStreamMode.Read)
        Dim sr As New IO.StreamReader(cs)

        Dim retStr As String
        retStr = sr.ReadLine

        sr.Close()
        cs.Close()

        Return retStr

    End Function

End Class

Public Class Form1
    Inherits System.Windows.Forms.Form

#Region " Windows フォーム デザイナで生成されたコード "

    Public Sub New()
        MyBase.New()

        ' この呼び出しは Windows フォーム デザイナで必要です。
        InitializeComponent()

        ' InitializeComponent() 呼び出しの後に初期化を追加します。

    End Sub

    ' Form は、コンポーネント一覧に後処理を実行するために dispose をオーバーライドします。
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub

    ' Windows フォーム デザイナで必要です。
    Private components As System.ComponentModel.IContainer

    ' メモ : 以下のプロシージャは、Windows フォーム デザイナで必要です。
    'Windows フォーム デザイナを使って変更してください。  
    ' コード エディタを使って変更しないでください。
    Friend WithEvents Button1 As System.Windows.Forms.Button
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Button1 = New System.Windows.Forms.Button
        Me.SuspendLayout()
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(64, 72)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(136, 32)
        Me.Button1.TabIndex = 0
        Me.Button1.Text = "Button1"
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 12)
        Me.ClientSize = New System.Drawing.Size(292, 266)
        Me.Controls.Add(Me.Button1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)

    End Sub

#End Region

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim cr As New Crypto
        Dim key As Byte() = {&H41, &H42, &H43, &H44, &H45, &H46, &H47, &H33, &H41, &H42, &H43, &H44, &H45, _
                             &H46, &H47, &H33, &H41, &H42, &H43, &H44, &H45, &H46, &H47, &H33, &H41, &H42, _
                             &H43, &H44, &H45, &H46, &H47, &H33}
        Dim iv As Byte() = {&H0, &H1, &H2, &H3, &H4, &H5, &H6, &H7, &H8, &H9, &HA, &HB, &HC, &HD, &HE, &HE}

        cr.Key = key
        cr.IV = iv

        Dim str As String = "12345678901234567"

        Console.WriteLine("元の値:" & str)

        Dim ret As Byte()
        ret = cr.Encrypt(str, 31)

        Dim retStr As String
        retStr = cr.Decrypt(ret)
        Console.WriteLine("結果:" & retStr)
    End Sub
End Class