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Another feature that I want to cover in this lecture is how to sign a file without encrypting it.

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So maybe you want to actually transfer this picture over the Internet, but you're okay with people

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seeing the content of the picture.

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You only want to make sure that the sender is able to verify that this picture was actually sent by

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you and that it was not modified since you created it.

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So this is similar to what the tails or the developers do when they create a new version of the application.

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And that's what I showed you at the start of the course when we were validating and making sure that

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the files that we downloaded did not get modified and are actually created by the Tor or the Tails creators.

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We can do this by simply signing the file without encrypting it, and we can do it also using Cleopatra.

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So again, I'm at David's computer here, as you can see with the one with the green background, you

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can see that I have David's key pair, the private and the public.

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And I only have John's public key.

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So what we want to do, we want to sign this image, this picture as David, but we don't want to encrypt

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it.

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So all we have to do is again, click on sign, encrypt, select the picture that we want to sign.

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And it's the same picture in here.

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And this time we want to sign it as David, but we don't want to encrypt it at all.

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So we don't want to take any of these boxes.

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And that's it.

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Now, as you can see, as a result, you're going to get a file that has the same picture name but ends

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with a dot sig with a dot sig extension short for signature.

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And once we click sign in here and the process is successful, you'll be able to see an extra file in

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the same location that we selected and it has the Sig file.

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So this is simply a signature for this file right here.

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This signature corresponds to this current version of the file.

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And if this file is modified in any way, shape or form, it will break the signature.

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Therefore, what we need to do now is send this file as is, along with the signature.

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As a result, people can make sure that this file did not get modified by validating this signature.

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So again, you can transfer this any way you want.

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We covered that previously.

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I'm going to pause the video and resume once I have it downloaded at John's computer.

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So now we're back to John's computer and I have the image sent as is unencrypted along with its signature

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right here.

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And assuming John was able to download this from the Internet.

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And all we want to do right now is make sure that this file or this picture did not get modified.

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And we're going to do this using the signature.

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It's very important to make sure that the file and the signature are stored in the same directory and

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have the same name.

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As you can see in here.

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We're just going to select the file and it will automatically find the signature within the same working

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directory.

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And doing this is very, very easy.

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Again, using tails, we're simply going to click on Decrypt Verify, we're going to select the file

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that we want to check its integrity In this example, it's this picture right here.

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We're going to click open and we're going to click on the audit log.

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And as you can see, it's telling us right now that there is a good signature from David again, meaning

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that this signature was created by David and that this picture did not get modified since this signature

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was created.

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Now, as you can see, I've only selected the picture when I was checking the signature because the

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signature exists in the same directory and it has the same name as the picture.

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So it is very important to have the picture and the signature in the same directory and have the same

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name.

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And this way it allows the sender to verify that this picture was actually sent by you and that it was

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not modified since you created it.