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Now that we understand the theory behind signatures in BGP.

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In this lecture, I want to show you how to practically verify the integrity of the message by checking

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the signature.

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So right here, I'm in John's computer and as you can see, his entry is in bold because we have the

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public and the private key for John.

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And in here for David, I have the public key of David.

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And that's why it's not bold.

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It's like all of the other public keys that we have, because as mentioned in the theory lecture, we

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need the public key of the sender in order to verify the integrity of the message.

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And obviously our own private key to decrypt the message.

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Now, right here, I have a message that is sent from David and signed by them using their own private

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key and encrypt it for me, for John, using my own public key.

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I'm not covering this in this lecture because previously when I showed you how to encrypt messages,

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I also covered how to sign them.

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As you can see in this flashback right here.

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So right now, I have the message.

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It's already signed using David's private key and encrypted using my own private key, using John's

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private key.

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So all I have to do in here is simply copy the message.

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And go to my notepad.

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Paste the message and we're going to click on Decrypt Verify Notepad.

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Now it's going to ask me for my own private key in order to decrypt the message, just like we seen

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earlier, because the message is actually encrypted using my public key, using John's public key.

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So I'm going to put the passphrase.

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And again, as we saw earlier, we can see the message decrypted in here.

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But that's not what we're here for.

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What we're here for is the signature.

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We want to make sure that David is actually the person that sent this message.

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And we should be able to do this, because this time, unlike the last time we actually imported David's

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public key in Cleopatra.

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So all I have to do now is click on the audit log in here.

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And as you can see, it's telling us that we have a good signature from David Smith.

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This means that whoever sent this message has the private key for David Smith.

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Therefore, we can be sure that David Smith is the person that actually sent this message so we can

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verify the integrity of the message and we can verify that the sender is actually the sender that they

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are claiming to be.

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Not only that, but we're also sure that the content of this message was not modified since it was created

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or composed by David or by the sender.

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Because as mentioned earlier, if the message gets modified, then this signature will not check out,

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the verification will fail.

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And knowing that the message did not get modified is very, very important because as mentioned earlier,

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when data is sent, it passes over a number of points where it can be modified.

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It can also be intercepted and modified by hackers or agencies.

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Therefore, checking the signature like this is really, really important to make sure that the message

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did not get modified since it was created.

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You can also see in here that it's saying the key is not certified with a trusted signature.

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This is fine.

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This is just because the key is not set to be trusted within Cleopatra.

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But the main thing is you want to make sure that it's saying that you got a good signature from the

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sender, that you're expecting this message to be sent from.

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So now, as a result, we are able to send encrypted messages that can only be read by the receiver.

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The receiver, on the other hand, can make sure that this message is actually sent from us, and they

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can also make sure that the message did not get modified since it was written or created or composed

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by us.