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OK so so far we learned how to use BGP to encrypt text and send it in a way so that the receiver is

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the only person that's able to read the content of the text.

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Not only that but we also learned how to sign the message to sign the text so that the receiver can

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verify that this message was actually sent from us from the center.

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So it's really really good because now when a message is sent we're sure that it can only be read by

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the receiver and the receiver can be sure that it was actually sent from the sender and he can also

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verify that the message did not get modified as it was sent.

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So this is really really good.

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The only problem is we can only do this for text so what if you wanted to send a document or an image.

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Therefore in this lecture I'm going to show you how to encrypt sign verify and decrypt files.

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So right here in John's computer I have the image that we already worked on and removed its metadata

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before.

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If you don't remember how to do that.

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Please go back to that lecture.

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And if I double click the image right now as you can see the image works it shows us a picture of a

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car.

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Now let's assume we want to send this message to David and we want to send it securely so that if anybody

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intercepts this message or if anybody manages to read it they want be able to see the content of it.

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They won't be able to see the image.

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To do that we're going to right click it and we're going to click on encrypt now you'll get a message

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that is very similar to what we used to get when we encrypt text.

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You need to select the public keys of the people that will be able to see the contents of this file.

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In my case I'm sending this to David.

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So I'm going to take David from here.

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And as we learned before you can also sign the message from here and select your own private key and

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that way when the receiver receives the image they can verify that the message or the image was sent

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from you by verifying it with your own public key.

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So I'm going to click on OK this will ask me for my passphrase for my private key because I selected

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design option if you did not select design option you will not see this and once I put the password

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as you can see I will have a new image created and this image doesn't really display it doesn't really

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work.

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So if I double click it you actually won't see anything in here.

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And the reason for that is because this image right now is encrypted and the only person that can see

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it is David.

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So we need David's private key in order to see the contents of this message.

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Therefore like I said right now we're in John's computer.

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So even John can't see the content of the image anymore and what we're going to do is we're going to

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go ahead and send this as an attachment in an email to David Smith at a blue dot in I'm gonna scroll

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down.

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I'm going to select the image and keep in mind you want to make sure you select the encrypted image

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not the normal image.

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So right here we have the normal decrypted image as you can see we can see it in here and the preview

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and right here we have the encrypted version of it that will not work unless we have the private key

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of David so I'm going to click on open and just say test in here and the content and click on send perfect

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now the message should be sent.

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So let's go to David's computer with the refresh the inbox we have a new message.

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Perfect.

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Let's go ahead and open it and we're going to download the attachment savoured it's going to go in my

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third browser directory that's fine.

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Click on Save and that's go ahead and open the containing folder.

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And as you can see we can't really see the contents of the image.

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Now this is the same whether this was a PDA f or a Word document or any file really I'm just using the

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image as an example.

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Now in order to decrypt this message because this is David's computer and because this message was specifically

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encrypted for David using David's public key we can actually decrypt it right here because because we

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have David's private key and we'll be able to see the contents of it.

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To do that we're going to right click the image we're going to click on open with decrypt file.

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This will ask you for the passphrase for David's private key.

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I'm going to input it

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on perfect as you can see.

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This will create a new file.

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This is the image after decryption and as you can see in the middle it said that the signature has been

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verified.

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So we're sure that this image was actually sent from John.

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Now I can double click the image to see its content.

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And as you can see I'm able to see the contents of the message.

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So the idea behind this is very similar to the idea of sending text we encrypted message with the receiver's

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public key.

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If anybody manages to get their hands on this file whether it's an image a PDA if a document doesn't

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really matter.

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They won't be able to read the content of the file unless they have the private key.

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Now there is also one more feature that I want to cover in this lecture which we can use to sign the

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file without encrypting it.

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So if you remember when we downloaded the Tor browser we also downloaded a signature and we use that

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signature to verify that the Tor browser did not get modified as we downloaded it.

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So you can also do this to any file you send by generating a separate signature.

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So again you can do this to any file you want whether it's software whether it's an image a PDA f a

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Microsoft document.

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It really doesn't matter.

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I'm using the image here as an example.

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John Wicks computer right now.

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And all you have to do is click the file that you want to sign click on sign it will ask you which private

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key you want to use to sign this file.

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Like I said I mean John Wilkes computer the only private key that I have right now on this computer

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is John Wick so the only entry I have in here is John Wick so I'm going to click on.

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OK.

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And as you can see with this will generate a new file with a dot Sig extension.

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This is a signature that corresponds to this file that has been generated using John Wilkes private

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key so people can use this file to make sure that the image did not get modified since this signature

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file was created by John Wick and to do this verification.

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They'll use John Wilkes Public Key so the private key is used to generate the signature the public key

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gets used to verify that the signature did not get modified.

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Now if you're doing this you will obviously have to send the signature file with the image file to the

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receiver.

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So let me do this really quick here again or send this to David Smith

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and like I said you want to make sure you first select the file that you want to send which in my case

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is the image and you also need to select the signature so I'm going to select the image first and then

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click on attach.

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And then I'm going to select the signature file as well like I said and we're gonna open and click on

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a touch again.

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And right now we have the two files added to the message.

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I'm going to click on sent to send the message.

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Now keep in mind right now we did not encrypt the image.

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If someone manages to intercept this file they'll be able to see the contents of the image.

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We only signed the image with the separate signature so the receiver can verify that the image did not

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get modified as we sent it.

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So go into the receiver's computer.

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Let's go refresh the inbox and we'll go open it open the new message and let me actually delete what

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I have in here for now and we're going to download the image

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and then we'll download the signature

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and go into the downloads directory as you can see straightaway we're able to see the contents of the

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image.

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So the image was not encrypted because all we did is we generated a signature for the image.

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So the whole purpose of this is to allow the receiver to verify that this message was sent by John and

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that the message did not get modified since John created the signature to do this.

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You're right click the signature and we're going to click on open with verify signature and as you can

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see it's telling us that this is a valid signature.

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And like I said the untrusted warning can be ignored.

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It literally just means that the key has not been set to trust it.

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But the fact that it is saying a valid signature means that this image did not get modified since John

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created this signature right here using his own private key so that's it for this lecture.

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I just wanted to show you how we can use PDP to encrypt files sign them so that they can then be verified

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and decrypted at the destination.

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And this way we're able to send files securely because even if they get intercepted while they're being

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transmitted whoever intercepts them they won't be able to read their content.

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Not only that the receiver will also be able to verify that the file did not get modified as it was

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sent and verify that it was sent from the right person not from a third party.