WEBVTT

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>> In this section,
we'll start to talk

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>> about cryptography.

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>> I think cryptography
is really interesting,

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but it's also a topic that
people get nervous about.

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But if you take it step-by-step,

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bit-by-bit, you'll find that
cryptography makes sense.

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You may have to hear some
of it multiple times.

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I think the questions
you find on the test for

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cryptography are

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actually more
straightforward than others.

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I hope cryptography
will click for you.

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Even if it doesn't the
first time, stick with it.

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The beauty of these
videos is that

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you can play them
multiple times.

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Now, we'll start talking
about the basics.

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I tried to teach
this topic as though

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my students have absolutely
no experience with it.

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Now, I know some of you may
have experience with it,

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but I find a lot of
people only know

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the parts that they'd
been exposed to,

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and maybe they don't have

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the full foundational
understanding.

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We're going to start
right at the beginning

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and define some of these terms:

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algorithms, keys,
initialization vectors,

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seeds, and salts,

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and what they mean,
and how they help

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us protect sensitive info.

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From there, we will build
on those ideas and look at

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practical
implementations through

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symmetric and asymmetric
cryptography.

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There's two ways to provide
obfuscation for our data,

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which means making
our data unreadable.

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But each of them have
different methods

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and different purposes,
so we need to understand

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>> the difference between those.

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>> Then just like
many other things,

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the best is right
there in the middle.

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If we take the good things about

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>> symmetric cryptography
and combine them

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>> with the good things about
asymmetric cryptography,

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>> we have a hybrid
cryptography,

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which is what most applications

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>> and secure protocols use.

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>> Then we're going to move on
to talking about integrity.

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One of the ways we get
integrity is through hashing.

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Hashing will create a digital
representation of a file.

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You can also take
that hash and add

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authenticity to it and
get non-repudiation.

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Non-repudiation is
a combination of

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authenticity and
integrity together.

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If we think about
that with an email,

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the sender can't
dispute having sent

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the message nor the
content of the message.

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Then you'll find out that
a hash is very limited.

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A public key infrastructure is

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needed to support
non-repudiation.

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That takes a lot of support.

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We may decide to use message
authentication codes

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or MACs to solve the
problem instead.

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MACs provide more
security than hash.

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You don't require
as much support

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and infrastructure
as non-repudiation.

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Now, Mac is one of

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the most fun acronyms
that is going

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to mean something
different every day.

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But for this module,

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the meaning is message
authentication code.

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Last but not least,
we're going to

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talk about some
email cryptosystems.

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We'll talk about PGP,

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which is proprietary
cryptosystem.

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Then we'll talk about S/MIME.

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This is a long chapter and I

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hope you find it as
interesting as I do.

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Now, starting with the
basics as promised,

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the first thing I
want to talk about is

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what cryptography does for us.

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Most people would say
that we need cryptography

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because we need privacy and

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>> we want to protect our data.

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>> But in addition to privacy,

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we also get
authenticity, integrity,

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>> and non-repudiation.

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>> Here's a quick overview of

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the services that
cryptography provides.

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Privacy: Prevents

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unauthorized disclosure
of information.

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Authenticity: Verifies
the claimed identity.

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Integrity: Detects
modification of corruption.

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Non-repudiation: Combines
authenticity and integrity.

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A sender can't
dispute having sent

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a message nor its contents.

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If in doubt and
you can't think of

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all the services that
cryptography provides,

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think of PAIN: privacy,

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authenticity, integrity,
non-repudiation.