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- Let's go over what are ciphers and keys

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in public key cryptography.

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And basically a cipher is a set of rules

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which can actually be
called an algorithm, right?

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They're also called algorithms.

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And basically there are rules
on how to perform encryption,

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or decryption of packets,
or decryption of emails,

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or, you know encryption or
decryption of files as well.

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Now, there are hundreds of
encryptions of algorithms

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that actually available out there, right?

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And there are likely many
more that are proprietary

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and used for special
purposes, such as, you know,

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government and national security.

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But some of the common methods
that's actually ciphers use

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as a whole is the method of substitution.

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Another method called polyalphabetic,

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and transposition as well, right?

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Now, there are also keys,

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and a key is a piece of information,

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or parameter, that actually specifies

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the output of a cryptographic algorithm.

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So you actually have a concept of a public

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and private key just as
we actually mentioned

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in the previous lesson.

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However, let's actually go over how

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that works in practice, right?

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So in this screen, I
actually have two entities,

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or two users.

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One is called Ben and the
other one is Pete, right?

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Typically in examples of cryptography,

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you will hear, you know, the word,

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or the name, Bob and Alice, right?

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So I wanted to be a
little bit more creative

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and just change names
and this is Ben and Pete.

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And then you actually may have

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an attacker in between, right?

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Let's just call that Eve.

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And Eve, and you will learn,

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you know, what eavesdrop attacks are.

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Eve will actually try to eavesdrop

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the conversation between
Ben and between Pete, right?

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There are many different ways

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on what you can encrypt traffic
between these two entities.

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One is by actually using VPN, right?

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Things like site-to-site VPN.

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You may actually have
two different routers,

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actually configure for IPv6,

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but in this case, it's actually looking

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at how Ben can actually send
an encrypted email, right?

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Specifically using a
protocol, or implementation,

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called Pretty Good Privacy,

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just as we mentioned before, so PGP.

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Now Ben will actually have a private,

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and a public key.

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And also Pete will actually
have a private and a public key.

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And Ben and Pete will actually change,

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or share, their public keys to each other.

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That means that for Ben to
be able to actually encrypt

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an email to Pete, he will
actually use his public key

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to encrypt that email.

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And then Pete will actually
use his private key

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to decrypt that email, right?

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So that's actually the main purpose

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of the public and private keys.

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Again, you actually keep your private key

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all the time with you.

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If that key is actually compromised,

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you actually have to regenerate
your key pair once again

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and revoke your keys.

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So that's the process of revocations

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and you will learn about revocation

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once we actually cover
digital certificates later

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in this course.