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Previously, we learned how to securely and privately send messages over the Internet.

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And we did this by encrypting and signing the message before sending it.

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This ensures that nobody can read the message except the sender that we encrypt the message for.

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And it also allows the sender to first of all, verify the integrity of the message, make sure that

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we are the senders and also using the signature, they can ensure that the message was not modified

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as it was transmitted.

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So all of that was great for text, but we still don't know how to do it for files and that's what I

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want to cover in this lecture.

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So in this lecture I'm going to show you how to sign, encrypt and decrypt files so that we can securely

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and privately send them over the Internet and make sure that they can only be seen by the person that

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we're sending this file to and also allow that person to verify the integrity of the message and verify

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the sender.

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Now, doing this is very easy.

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Right here I am in David's computer.

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This is the file, the image that I want to send.

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And I have Cleopatra running in here.

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As you can see, I have David's private and public key because, like I said, this is David's computer

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and I only have John's public key because John is the person that I'm going to be sending this message

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to.

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So he's the receiver.

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Now, the file right here, as you can see, it's visible.

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It works.

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It's a picture of me and my cat.

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And what we want to do is we want to encrypt this so that the content of this image is invisible to

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anybody that does not have the private key of John, because I'm going to be sending this to John.

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Now, doing this is very easy.

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We're simply going to go back to Cleopatra and we're going to click on Sign Encrypt.

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It's going to ask me to select the file that I want to sign or encrypt.

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So we're going to go to Amnesia pictures.

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That's what I have the picture.

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And this is the picture right here.

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22 dot JPG.

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You should also remove all metadata from this picture and I cover that earlier in the course.

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So right now this picture is ready to be encrypted.

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So I'm going to click on Open and we're going to have a dialog similar to what we had when we were encrypting

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text.

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So first of all, it's asking us who do we want to sign this picture as?

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So we're going to be using our private key to sign it.

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This allows John to verify the sender of the message.

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We're also going to be encrypting the message so that, like I said, if it gets intercepted, its content

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will be invisible unless you have the private keys that we select here.

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So we're encrypting it for ourselves so we can see it ourselves and we're also going to encrypt it for

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others.

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And like I said, the receiver is John, so I'm going to put John's key in here.

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As you can see, you just have to click it and that's it.

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I don't want to set a password, so I'm not going to tick this box.

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And the output in here specifies where the encrypted message will be stored.

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And as you can see, it's going to be stored in home amnesia pictures and it's going to be called 22

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dot jpg dot jpg.

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So that's how you know that it is encrypted.

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So it's basically going to be stored in here in this same location.

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So once we're happy, we're going to click, sign, encrypt.

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It's going to ask us for the private key of David because we're signing it using the private key of

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David.

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So I'm going to input that click okay and perfect.

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As you can see, it's telling us that the picture is signed and encrypted.

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So we're going to click finish here.

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And if you look in here in the directory that we selected, you can see that we have a new file with

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the same name that we selected in the output.

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So 22 dot jpg dot jpg And as you can see, we cannot see the content of this picture.

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So nobody will be able to see the content of this picture unless they decrypt it using either the private

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key of David or the private key of John.

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These are the private keys that we selected when we encrypted the image.

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So now we can go ahead and send this picture to John and you can be rest assured that nobody will be

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able to see the content of this picture unless they have the private key of John.

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Therefore, they should be the only person that is able to see it.

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Now you can share it using any method of transferring files that we covered earlier.

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I'm not going to waste your time showing you how to do that.

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We already covered that.

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So I'm going to pause the video and resume it after I transfer it to John's computer.

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So we're here at John's computer and I've already downloaded the encrypted image.

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As you can see, it's not visible.

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Now, in order to see it, we're going to go to Cleopatra.

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And as you can see, because I'm in John's computer, I've got the key pair for John.

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I got the private and the public key, and I only have David's public key.

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Now we want to decrypt a message or a file.

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So we're going to click on Decrypt Verify in here, and we're going to select the image or the file

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that we want to decrypt.

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And it's stored in my downloads.

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And this is the file right here.

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Double click.

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And as you can see, it's asking me for the passphrase for John's private key because this file was

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encrypted using John's public key.

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And in order to decrypt it, we need the private key.

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So I'm going to input that very quickly.

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And perfect.

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As you can see, the operation is complete.

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So the decryption is complete.

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It's telling us that this was signed using David's key.

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And if we click on the show audit log, you can see that we have a good signature from David.

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So as we mentioned earlier, this is what we usually look for.

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And basically this means that this file was signed using David's private key.

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It verifies that David is the creator of the file, and it also verifies that the file did not get modified

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since David created it.

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That means we're happy with the file.

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So we're going to close this.

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And looking in here in the output field, it's telling us that the decrypted message is going to be

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stored in the downloads directory, which is the directory that actually contains the original encrypted

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message.

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So we're happy with that.

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We're going to say save all and perfect.

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As you can see, we have the file in here decrypted.

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So if we double click it, we'll be able to see the contents of the file.

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Now we're using an image in this example, but you can use this method to decrypt any file, whether

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it's an image, a word document, a PDF, a video.

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It doesn't really matter.

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You can use the exact same steps to encrypt and sign files, and this way it allows us to send the files

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securely and make sure that no one is able to see it except the person that we're encrypting this file

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for.

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And it also allows that person to verify that this file was created by us and verify that this file

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did not get modified since it was created by us.