# Encryption Part 2

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>> Let's take an example

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here and we're going to do some math.

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I'm going to keep it as simplistic

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as possible and keep in

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mind that this isn't

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the actual math that's used in today's algorithms.

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This is just an example.

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What I want to show you here,

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the idea is here,

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is how you need to choose

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an encryption algorithm that's strong,

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that's a more complex and

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a stronger algorithm than others.

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Let's take a very basic formula here.

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What have we have an algorithm of K plus

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3 equals C. That means we're saying K is the key,

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that's the secret and C is the cipher text.

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C is just the result of the algorithm.

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We take that and we use that to

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encrypt data and we transmit that.

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We'll see our cipher text is 8.

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If we have an intruder who's listening

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in on the wire and he sees

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that C equals 8 and he knows what algorithm's being used.

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Well, now he can reverse engineer it.

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He knows the algorithm is K plus

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3 equals C. In this case, C is 8.

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He knows that our key plus 3

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equals 8 and he can figure out pretty easily

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that our key is 5 and now he can use

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that key to decrypt

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anything else that we sent across the wire.

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This would be an example of a weak algorithm.

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When you choose an algorithm,

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you want to choose one that's much stronger.

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Here's a fictitious example of a stronger algorithm.

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In this case, we've got an algorithm that's

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actually two different parts.

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The equation is broken into two different parts.

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On the left side, we've got 5

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plus K1 and K1 is part of our key.

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Maybe our key is 12 characters long,

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and we're going to use the first six characters

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as our partial key and

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use that in the first part of the equation.

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So 5 plus partial key minus

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the data itself equals some variable, which is X.

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Since we know what the key

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is and we know what the data is,

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we can solve for X,

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and then we can take X and we can put it into

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the second equation and say X plus

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45 minus the second part of

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the key equals our actual cipher text.

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There's much more layers to

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this algorithm than they were to

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the other one and this is a much more

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complex way to encrypt data.

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Now we take that and we transmit that data.

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Our cipher text is still 8.

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But this time if we have somebody listening on

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the wire and they see

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that our cipher text is 8 and they say,

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we're going to try to reverse engineer this.

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I know what the algorithm is that they're using.

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I know the cipher text.

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We're going to replace our cipher text with eight.

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Now the intruder says,

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"Well now I can reverse engineer and X plus

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45 minus a part of the key. I don't know.

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I don't have any idea.

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It's too complicated. I can't decrypt it.

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It remains a secret."

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It's important to choose

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a strong algorithm whenever you're choosing one.

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The two most common algorithms today are RSA.

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RSA stands for Rivest-Shamir-Adleman and those are

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the last names of

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the three mathematicians that invented that algorithm.

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Chances are today, if you type in https colon slash

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slash something and you're going to make

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a secure connection to some Internet site,

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it's using the RSA algorithm.

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It's one of the most widely used algorithms on

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the Internet today, still very secure.

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Another one is AES,

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which stands for Advanced Encryption Standard.

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That's one actually that the military uses,

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that's been recognized by the military as

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the strongest encryption algorithm out there today.

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There's a lot of other things happening today.

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There's quantum encryption that's

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being talked about and things that are very complicated.

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Encryption can be an entire subject by itself.

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I put an example down below here on this slide,

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this is the actual RSA encryption algorithm.

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You can see it's much more complicated than

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that A plus B equals C that we were talking about,

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which is what makes it such a strong algorithm.

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It's why it's been around for decades.

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A little bit about symmetric versus

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asymmetric encryption.

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Symmetric encryption, as we said,

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is when both parties use the same key.

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Both sides have to know what that key is.

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We've talked a little bit about that in our VPN lesson

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when we talked about PPTP

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or point-to-point tunneling protocol.

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In that case, both sides had

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the same key and they just use that to

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encrypt the data or create that tunnel.

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It is faster than asymmetric encryption,

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but it's faster because both sides know the key.

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They don't have to negotiate to figure out

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what key to use for encryption. They already know it.

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It's one less step that has

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to happen during transmission.

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Therefore, it's faster,

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but it requires each party to keep those keys secret.

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Not only does that key exists in two places,

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but now there's a bunch of other people that

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know what those keys are so it's

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a lot more likely

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that those secrets are going to get dispersed,

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are going to get found out somehow.

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Asymmetric encryption is a method by

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which each party has a different key.

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The keys are mathematically

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related and we're going to talk

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about that in a little while.

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But one party has one key that encrypts the data,

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the other side has a completely different key that's

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mathematically related to the first key to decrypt it.

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But even though they're mathematically related,

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you cannot derive one from the other.

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If you get your hands on this key and you steal it,

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you can't figure out what this other key is.

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You need both keys to see the whole conversation.

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You may see a conversation one way

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with key encrypted and this one decrypted.

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Where the conversation the other way is vice versa,

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so you need both keys to steal the data.

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They are mathematically related

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but can't be derived from each other.

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Let's talk about public key encryption.

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In a public key encryption system,

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the best way I can describe this is to use an example,

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and most of the Internet uses public key encryption.

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Public key encryption is used

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mainly because it wouldn't be

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very efficient to use

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a symmetric key encryption system on the Internet.

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If amazon.com had to keep

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a separate key for

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every human being that might connect to them,

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they would have billions of keys

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that they would have to maintain,

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and that's just not very

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efficient and not very effective.

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So in public key encryption, the way that works,

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let's say Bob over here on

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the left wants to send an email to Jack,

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but he wants to do it in a secure manner.

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He wants to encrypt that email,

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so if somebody intercepts

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along the way, they can't read it.

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In a public key encryption system

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both parties are going to have a pair of keys.

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They're each going to have their own pair of keys.

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Bob is going to have both a public and a private key.

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His private key, he's going to keep private.

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No one but Bob will ever know Bob's private key.

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His public key is public.

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Anyone can see Bob's public key, same with Jack.

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Jack is going to have a public and a private key.

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Now remember these keys are mathematically

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related to one another.

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In the beginning of a transaction,

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what they're going to do when they set up encryption is

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they're going to exchange public keys.

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Bob is going to send Jack his public key.

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Jack is going to send Bob his public key.

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Now Bob has his own initial key pair,

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his public and private key,

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but he also has Jack's public key and vice versa,

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Jack has his initial pair plus Bob's public key.

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Now once a key exchange happens,

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Bob can now create a message.

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His message at first is unencrypted.

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When he wants to encrypt that message,

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he can apply, he can encrypt it using Jack's public key.

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Bob created the message.

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He's going to use Jack's public key

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to encrypt that message.

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When he transmits it,

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it's encrypted, it's copper text on the wire.

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If someone intercepts it, they can't read it.

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When Jack receives it.

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Jack is the only person on

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the planet that has Jack's private key.

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Bob encrypts the message with Jack's public key,

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which is mathematically related to Jack's private key.

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So therefore, when Jack received the message,

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he could decrypt it with his own private key.

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When Jack wants to respond to that message,

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he's going to encrypt it with

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Bob's public key and the same thing happens in reverse,

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goes across the wire, encrypted,

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Bob receives it and in order to decrypt it,

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he's going to use his own private key to decrypt it.

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He's the only one that can do that

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because he's the only one that has the key.

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That's how public key encryption works.

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Encryption can be a very deep subject.

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There's a lot of math,

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there's a lot of subtleties.

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We're not going to get into any of that today,

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but I wanted you to understand at

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a very high level how encryption works,

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what some of the different types of encryptions are,

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how they're applied in

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the environment and just a general idea of encryption.

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That wraps up this session on encryption.

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Next up, we're going to talk about web proxies.

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