WEBVTT 00:01.290 --> 00:01.710 Okay. 00:01.710 --> 00:10.680 So so far we learned how to use BGP to encrypt text and send it in a way so that the receiver is the 00:10.680 --> 00:14.790 only person that's able to read the content of the text. 00:14.820 --> 00:21.540 Not only that, but we also learned how to sign the message, to sign the text so that the receiver 00:21.540 --> 00:26.150 can verify that this message was actually sent from us, from the sender. 00:26.160 --> 00:31.740 So it's really, really good because now when a message is sent, we're sure that it can only be read 00:31.740 --> 00:37.410 by the receiver and the receiver can be sure that it was actually sent from the sender. 00:37.410 --> 00:42.730 And he can also verify that the message did not get modified as it was sent. 00:42.750 --> 00:45.180 So this is really, really good. 00:45.210 --> 00:48.840 The only problem is we can only do this for text. 00:49.020 --> 00:52.680 So what if you wanted to send a document or an image? 00:52.710 --> 00:59.850 Therefore, in this lecture, I'm going to show you how to encrypt, sign, verify and decrypt files. 01:01.050 --> 01:09.210 So right here in John's computer, I have the image that we already worked on and removed its metadata 01:09.210 --> 01:09.850 before. 01:09.870 --> 01:13.500 If you don't remember how to do that, please go back to that lecture. 01:13.500 --> 01:17.400 And if I double click the image right now, as you can see, the image works. 01:17.400 --> 01:19.410 It shows us a picture of a car. 01:20.040 --> 01:26.460 Now, let's assume we want to send this message to David and we want to send it securely so that if 01:26.460 --> 01:33.030 anybody intercepts this message or if anybody manages to read it, they won't be able to see the content 01:33.030 --> 01:33.480 of it. 01:33.480 --> 01:35.970 They won't be able to see the image. 01:36.060 --> 01:40.680 To do that, we're going to right click it and we're going to click on Encrypt. 01:42.350 --> 01:47.280 Now you'll get a message that is very similar to what we used to get when we encrypt text. 01:47.300 --> 01:53.870 You need to select the public keys of the people that will be able to see the contents of this file. 01:54.260 --> 01:58.850 In my case, I'm sending this to David, so I'm going to take David from here. 01:58.850 --> 02:06.100 And as we learned before, you can also sign the message from here and select your own private key. 02:06.110 --> 02:12.350 And that way, when the receiver receives the image, they can verify that the message or the image 02:12.350 --> 02:17.030 was sent from you by verifying it with your own public key. 02:17.570 --> 02:19.100 So I'm going to click on. 02:19.100 --> 02:19.880 Okay. 02:20.990 --> 02:27.340 This will ask me for my passphrase, for my private key, because I selected the sign option. 02:27.350 --> 02:30.740 If you did not select the sign option, you will not see this. 02:32.380 --> 02:38.230 And once I put the password, as you can see, I will have a new image created. 02:38.240 --> 02:41.830 And this image doesn't really display it doesn't really work. 02:41.830 --> 02:46.300 So if I double click it, you actually won't see anything in here. 02:46.300 --> 02:53.380 And the reason for that is because this image right now is encrypted and the only person that can see 02:53.380 --> 02:54.460 it is David. 02:54.460 --> 03:00.070 So we need David's private key in order to see the contents of this message. 03:00.100 --> 03:05.680 Therefore, like I said, right now we're in John's computer, so even John can't see the content of 03:05.680 --> 03:06.880 the image anymore. 03:07.030 --> 03:13.570 And what we're going to do is we're going to go ahead and send this as an attachment in an email to 03:13.570 --> 03:17.650 David Smith at the blue dot in. 03:18.910 --> 03:20.200 I'm going to scroll down. 03:20.200 --> 03:21.910 I'm going to select the image. 03:23.010 --> 03:28.860 And keep in mind you want to make sure you select the encrypted image, not the normal image. 03:28.860 --> 03:32.010 So right here we have the normal decrypted image, as you can see. 03:32.010 --> 03:38.070 We can see it in here and the preview and right here we have the encrypted version of it that will not 03:38.070 --> 03:41.820 work unless we have the private key of David. 03:42.690 --> 03:49.680 So I'm going to click on Open and just say Test in here and the content and click on Send. 03:51.450 --> 03:51.990 Perfect. 03:51.990 --> 03:53.450 Now the message should be sent. 03:53.460 --> 03:55.770 So let's go to David's computer. 03:55.800 --> 03:57.720 We'll refresh the inbox. 03:58.950 --> 04:00.180 We have a new message. 04:00.180 --> 04:00.810 Perfect. 04:00.810 --> 04:02.490 Let's go ahead and open it. 04:04.350 --> 04:06.600 And we're going to download the attachment. 04:08.020 --> 04:09.010 Save it. 04:09.990 --> 04:12.180 It's going to go in my browser directory. 04:12.180 --> 04:12.930 That's fine. 04:12.930 --> 04:17.730 Click on Save and let's go ahead and open the containing folder. 04:18.480 --> 04:22.290 And as you can see, we can't really see the contents of the image. 04:22.590 --> 04:27.540 Now this is the same whether this was a PDF or a word document or any file. 04:27.540 --> 04:34.800 Really, I'm just using the image as an example now in order to decrypt this message, because this 04:34.800 --> 04:41.640 is David's computer and because this message was specifically encrypted for David using David's public 04:41.640 --> 04:47.940 key, we can actually decrypt it right here because we have David's private key and we'll be able to 04:47.940 --> 04:49.470 see the contents of it. 04:50.070 --> 04:52.320 To do that, we're going to right click the image. 04:52.320 --> 04:56.340 We're going to click on Open with Decrypt File. 04:57.030 --> 05:01.470 This will ask you for the passphrase for David's private key. 05:01.500 --> 05:02.850 I'm going to input it. 05:06.590 --> 05:07.370 I'm perfect. 05:07.370 --> 05:10.120 As you can see, this will create a new file. 05:10.130 --> 05:12.800 This is the image after decryption. 05:13.160 --> 05:18.440 And as you can see in the middle, it said that the signature has been verified. 05:18.440 --> 05:22.940 So we're sure that this image was actually sent from John. 05:23.270 --> 05:29.240 Now I can double click the image to see its content and as you can see, I'm able to see the contents 05:29.240 --> 05:30.320 of the message. 05:30.860 --> 05:35.060 So the idea behind this is very similar to the idea of sending text. 05:35.060 --> 05:38.720 We encrypt the message with the receiver's public key. 05:38.780 --> 05:44.990 If anybody manages to get their hands on this file, whether it's an image, a PDF, a document doesn't 05:44.990 --> 05:45.740 really matter. 05:45.740 --> 05:51.320 They won't be able to read the content of the file unless they have the private key. 05:52.130 --> 05:58.400 Now, there is also one more feature that I want to cover in this lecture, which we can use to sign 05:58.400 --> 06:00.860 the file without encrypting it. 06:00.950 --> 06:07.610 So if you remember when we downloaded the Tor browser, we also downloaded a signature and we use that 06:07.610 --> 06:13.490 signature to verify that the Tor browser did not get modified as we downloaded it. 06:13.670 --> 06:19.610 So you can also do this to any file you send by generating a separate signature. 06:19.610 --> 06:24.950 So again, you can do this to any file you want, whether it's software, whether it's an image, a 06:24.950 --> 06:27.470 PDF, a microsoft document. 06:27.470 --> 06:28.940 It really doesn't matter. 06:28.940 --> 06:35.570 I'm using the image here as an example at John Wick's computer right now, and all you have to do is 06:35.570 --> 06:39.260 click the file that you want to sign, click on sign. 06:40.740 --> 06:45.000 It will ask you which private key you want to use to sign this file. 06:45.030 --> 06:47.370 Like I said, I'm in John Wick's computer. 06:47.370 --> 06:51.530 The only private key that I have right now on this computer is John Wick. 06:51.540 --> 06:54.590 So the only entry I have in here is John Wick. 06:54.600 --> 06:55.860 So I'm going to click on. 06:55.860 --> 06:56.640 Okay. 06:57.270 --> 07:04.200 And as you can see, this will generate a new file with a dot sig extension. 07:04.470 --> 07:11.760 This is a signature that corresponds to this file that has been generated using John Wick's private 07:11.760 --> 07:12.240 key. 07:12.240 --> 07:20.310 So people can use this file to make sure that the image did not get modified since this signature file 07:20.310 --> 07:22.370 was created by John Wick. 07:22.380 --> 07:26.940 And to do this verification, they'll use John Wick's public key. 07:26.940 --> 07:29.940 So the private key is used to generate the signature. 07:29.940 --> 07:35.490 The public key gets used to verify that the signature did not get modified. 07:35.970 --> 07:42.450 Now, if you are doing this, you will obviously have to send the signature file with the image file 07:42.480 --> 07:43.770 to the receiver. 07:43.770 --> 07:46.080 So let me do this really quick here. 07:47.370 --> 07:49.710 Again, we're sending this to David Smith. 07:53.160 --> 07:58.860 And like I said, you want to make sure you first select the file that you want to send, which in my 07:58.860 --> 08:00.300 case is the image. 08:00.330 --> 08:03.360 And you also need to select the signature. 08:04.830 --> 08:13.470 So I'm going to select the image first and then click on attach and then I'm going to select the signature 08:13.470 --> 08:15.450 file as well, like I said. 08:15.450 --> 08:20.820 And we're going to open and click on Attach again. 08:22.080 --> 08:25.350 And right now we have the two files added to the message. 08:25.350 --> 08:27.840 I'm going to click on Send to send the message. 08:28.440 --> 08:32.340 Now, keep in mind right now, we did not encrypt the image. 08:32.340 --> 08:38.160 If someone manages to intercept this file, they'll be able to see the contents of the image. 08:38.160 --> 08:44.910 We only sign the image with a separate signature so the receiver can verify that the image did not get 08:44.910 --> 08:46.920 modified as we sent it. 08:47.730 --> 08:50.760 So go into the receiver's computer. 08:50.760 --> 08:54.960 Let's go refresh the inbox and we'll go open it. 08:56.750 --> 08:58.580 Open the new message. 09:00.670 --> 09:03.910 And let me actually delete what I have in here for now. 09:05.680 --> 09:07.990 And we're going to download the image. 09:11.890 --> 09:13.990 And then we'll download the signature. 09:18.380 --> 09:20.210 And go into the downloads directory. 09:20.210 --> 09:24.260 As you can see straight away, we're able to see the contents of the image. 09:24.260 --> 09:30.450 So the image was not encrypted because all we did is we generated a signature for the image. 09:30.470 --> 09:37.970 So the whole purpose of this is to allow the receiver to verify that this message was sent by John and 09:37.970 --> 09:40.190 that the message did not get modified. 09:40.190 --> 09:47.540 Since John created the signature to do this, you right click the signature and we're going to click 09:47.540 --> 09:49.790 on Open with Verify Signature. 09:51.040 --> 09:54.850 And as you can see, it's telling us that this is a valid signature. 09:54.850 --> 09:58.660 And like I said, the untrusted warning can be ignored. 09:58.690 --> 10:03.250 It literally just means that the key has not been set to trust it. 10:03.250 --> 10:10.210 But the fact that it is saying a valid signature means that this image did not get modified since John 10:10.210 --> 10:15.280 created this signature right here using his own private key. 10:16.510 --> 10:17.950 So that's it for this lecture. 10:17.950 --> 10:26.440 I just wanted to show you how we can use BGP to encrypt files, sign them so that they can then be verified 10:26.440 --> 10:28.630 and decrypted at the destination. 10:28.630 --> 10:35.710 And this way we're able to send files securely, because even if they get intercepted while they're 10:35.710 --> 10:40.750 being transmitted, whoever intercepts them, they won't be able to read their content. 10:40.960 --> 10:47.560 Not only that, the receiver will also be able to verify that the file did not get modified as it was 10:47.560 --> 10:53.440 sent, and verify that it was sent from the right person, not from a third party.