WEBVTT 00:01.020 --> 00:06.750 So far as we are going through the course, we interacted with the file system quite often. 00:06.960 --> 00:13.860 We also learned how to download and upload files, how to share files securely with friends and contacts, 00:14.100 --> 00:20.340 how to remove metadata that can be used to anonymize us or get information about us. 00:20.610 --> 00:27.450 So before moving to the next section, I think there is still one missing piece, which is how to properly 00:27.450 --> 00:30.480 delete files and wipe storage media. 00:31.200 --> 00:38.160 Now in general, in operating systems, when you right click a file and delete it, or even if you delete 00:38.160 --> 00:44.910 it and empty your recycle bin or your trash, the file doesn't actually get deleted. 00:45.090 --> 00:52.950 What happens is the operating system marks the file or marks the space that the file was occupying on 00:52.950 --> 00:55.620 the storage device as available. 00:56.100 --> 01:04.830 So the data of that file will still exist on your storage device until that space is overwritten with 01:04.830 --> 01:05.790 other data. 01:06.360 --> 01:12.900 That's why we see so many tools that are very easy to use that you can use to recover deleted files. 01:13.470 --> 01:18.660 Now, these are very simple tools that you can download from the Internet for free, so you can only 01:18.660 --> 01:21.780 imagine what a resourceful adversary can do. 01:22.560 --> 01:30.120 So because deleting a file doesn't actually delete the content of it or its data unless it's overwritten 01:30.120 --> 01:31.170 with other data. 01:31.200 --> 01:38.130 There are tools that will randomly fill up that space of that file with random data so that it's more 01:38.130 --> 01:40.200 difficult to recover that file. 01:40.740 --> 01:45.590 Now, Thales comes with such tools preinstalled, as you'd expect. 01:45.600 --> 01:48.030 So if we go to our file manager. 01:49.150 --> 01:51.390 And go to the file that we want to delete. 01:51.400 --> 01:54.760 So in my case, it's in files. 01:56.670 --> 01:58.380 It's this image right here. 01:58.680 --> 02:04.200 Now I can right click the image and just click on Move to Trash, which will literally just move it 02:04.200 --> 02:07.230 to trash similar to any other operating system. 02:07.230 --> 02:10.340 And then I'd have to go to the trash, right click and empty. 02:10.350 --> 02:16.920 And like I said, this will still not delete the content of this image or the data of this image from 02:16.920 --> 02:17.850 my storage. 02:18.720 --> 02:25.380 The better option to go to if you want to securely remove this file is to click on Wipe right here. 02:26.190 --> 02:33.090 Now if you click on that and expand the options in here, you'll see that it will ask you for the number 02:33.090 --> 02:41.880 of passes of random data that will be executed to overwrite the location that contains the data of this 02:41.880 --> 02:42.540 image. 02:42.870 --> 02:47.820 So by default, this is set to two, which should be good enough for most hard disks. 02:48.210 --> 02:54.390 You can set it to 38 for older ones, or one which is not very secure, which will only protect you 02:54.390 --> 02:58.080 from the very simple software that you can download on the internet. 02:58.710 --> 03:06.960 Now, this method will work on hard drives, but it won't work on USB sticks or solid state drives. 03:07.200 --> 03:12.660 Now, if you don't know the difference between hard drives and solid state drives, then I highly recommend 03:12.660 --> 03:14.760 you go and do some reading on that. 03:14.790 --> 03:21.060 I will include links in the resources of this lecture, but basically the way that solid state drives 03:21.060 --> 03:23.130 work, they don't have sectors. 03:23.130 --> 03:26.130 They use cells in order to store your data. 03:26.220 --> 03:33.630 And even if we use a tool similar to this tool right here in order to overwrite a specific location 03:33.630 --> 03:41.190 of this solid storage device, the logic inside the storage device will probably overwrite the request 03:41.190 --> 03:45.840 that we make in order to increase the life of the device. 03:46.620 --> 03:52.530 Therefore, you might use this click on wipe and think that it works, but it might actually not work 03:52.530 --> 03:54.090 as you would expect it. 03:54.540 --> 04:01.710 So you can only properly rely on this method if you're using a hard drive and not a solid state drive 04:01.710 --> 04:03.420 or a USB device. 04:03.990 --> 04:11.280 Now that's for removing one specific file, but what if we wanted to clean all the free space or all 04:11.280 --> 04:13.920 of the available space on the system? 04:14.460 --> 04:19.770 Now, this is only relevant if you're using persistence, obviously, and you might want to do this 04:19.770 --> 04:23.100 because you've deleted a number of files insecurely. 04:23.100 --> 04:28.620 So by literally moving them to trash and empty in the trash and then the contents of these files, like 04:28.620 --> 04:32.430 I said, will still be recoverable from your storage device. 04:32.970 --> 04:38.910 Therefore, what you want to do is you want to right click any empty space in your file manager, click 04:38.910 --> 04:45.540 on wipe available disk space and you'll get a very similar window to the one that we just got with the 04:45.540 --> 04:46.530 same options. 04:46.530 --> 04:53.490 And once you set the options, you click on wipe and that'll clean and that'll securely clean the available 04:53.490 --> 04:56.930 disk space so it won't delete the files that you have. 04:56.940 --> 05:03.450 It will only clean the available disk space, filling it with random data to make sure that it can't 05:03.450 --> 05:06.300 be used to recover the files that you deleted. 05:06.300 --> 05:09.740 So it will only clean the files that you deleted. 05:09.740 --> 05:16.620 It won't affect anything that you already have on your storage device that you did not delete yourself. 05:17.310 --> 05:24.210 Now this is great, but again, it won't work as expected when it comes to solid state devices and to 05:24.210 --> 05:27.870 USB devices for the same reason that I mentioned earlier. 05:28.440 --> 05:35.640 Therefore, if you're using a solid state device or a USB device and you want to securely delete all 05:35.640 --> 05:39.150 of the data that you have on it, then you have two options. 05:39.150 --> 05:42.360 First option is physically destroy that device. 05:42.360 --> 05:46.560 So you can burn it, put it in a microwave, do whatever you want, really. 05:46.800 --> 05:52.650 Or the other option is to securely format the device and wipe it. 05:53.100 --> 05:56.430 And I'm going to show you how to do that in the next lecture.