尝试解密时，Base-64字符串中的无效字符

Invalid character in a Base-64 string

   Public Shared Function DecryptUserString(ByRef cipheredText As String, ByRef password As String) As String
      Dim RijndaelManagedObj As New RijndaelManaged
      Dim RijndaelEncObj As ICryptoTransform, MD5Obj As New MD5CryptoServiceProvider
      Dim DecryptedBytes As Byte(), EncryptedData As Byte()
      Dim PasswordBytes As Byte() = New ASCIIEncoding().GetBytes(password)
      Dim UTF8Encoding As System.Text.Encoding = System.Text.Encoding.UTF8

      \'A modified Base64 is sent with ~ and -  so it can be sent as a form post
      EncryptedData = Convert.FromBase64String(Replace(Replace(cipheredText, \"~\", \"+\"), \"-\", \"=\"))

      RijndaelManagedObj.BlockSize = 128
      RijndaelManagedObj.KeySize = 128
      RijndaelManagedObj.Mode = CipherMode.ECB
      RijndaelManagedObj.Padding = PaddingMode.None
      RijndaelManagedObj.Key = MD5Obj.ComputeHash(PasswordBytes)
      RijndaelEncObj = RijndaelManagedObj.CreateDecryptor()

      DecryptedBytes = RijndaelEncObj.TransformFinalBlock(EncryptedData, 0, EncryptedData.Length)

      If DecryptedBytes.Length > 0 Then
         DecryptUserString = UTF8Encoding.GetString(DecryptedBytes, 0, DecryptedBytes.Length)
         If DecryptedBytes.Length = 0 Then DecryptUserString = New ASCIIEncoding().GetString(DecryptedBytes)
      Else
         DecryptUserString = \"\"
      End If
   End Function

  Private Function ReadText(ByVal TextFilePath As String) As String
    Using ReadStream As FileStream = File.OpenRead(TextFilePath)
      Dim FileTextBuilder As New StringBuilder()
      Dim DataTransit As Byte() = New Byte(ReadStream.Length) {}
      Dim DataEncoding As New UTF8Encoding(True)
      While ReadStream.Read(DataTransit, 0, DataTransit.Length) > 0
          FileTextBuilder.Append(DataEncoding.GetString(DataTransit))
      End While
      Return FileTextBuilder.ToString()
    End Using
  End Function