Dateientschlüsselung mit Rijndael

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

Public Function DecryptFile(ByVal sSource As String, ByVal sTarget As String, ByVal sPassword As String, Optional ByVal BufferSize As Long = 4096) As Boolean
    Try
        Dim sKey As Byte() = (New UnicodeEncoding).GetBytes(sPassword.PadRight(8, "*"))
        Dim OldFileStream As New FileStream(sSource, FileMode.Open)
        Dim NewFileStream As New FileStream(sTarget, FileMode.Create)
        Dim RijndaelManaged As New RijndaelManaged
        Dim CryptoStream As New CryptoStream(OldFileStream, RijndaelManaged.CreateDecryptor(sKey, sKey), CryptoStreamMode.Read)

        Dim Data(BufferSize) As Byte
        Dim Buffer As Long
        Dim BufferCount As Long
        Dim FileLen As Long = OldFileStream.Length

        Do
            If BufferCount >= FileLen - BufferSize Then
                ReDim Data(FileLen - BufferCount)
                Buffer = CryptoStream.Read(Data, 0, FileLen - BufferCount)
                NewFileStream.Write(Data, 0, Buffer)
                Exit Do
            End If

            Buffer = CryptoStream.Read(Data, 0, BufferSize)
            NewFileStream.Write(Data, 0, BufferSize)
            BufferCount += Buffer
        Loop

        NewFileStream.Close()
        CryptoStream.Close()
        OldFileStream.Close()
    Catch
        Return False
    End Try
    Return True
End Function