>> In this section, we'll start to talk
>> about cryptography.
>> I think cryptography is really interesting,
but it's also a topic that people get nervous about.
But if you take it step-by-step,
bit-by-bit, you'll find that cryptography makes sense.
You may have to hear some of it multiple times.
I think the questions you find on the test for
cryptography are
actually more straightforward than others.
I hope cryptography will click for you.
Even if it doesn't the first time, stick with it.
The beauty of these videos is that
you can play them multiple times.
Now, we'll start talking about the basics.
I tried to teach this topic as though
my students have absolutely no experience with it.
Now, I know some of you may have experience with it,
but I find a lot of people only know
the parts that they'd been exposed to,
and maybe they don't have
the full foundational understanding.
We're going to start right at the beginning
and define some of these terms:
algorithms, keys, initialization vectors,
seeds, and salts,
and what they mean, and how they help
us protect sensitive info.
From there, we will build on those ideas and look at
practical implementations through
symmetric and asymmetric cryptography.
There's two ways to provide obfuscation for our data,
which means making our data unreadable.
But each of them have different methods
and different purposes, so we need to understand
>> the difference between those.
>> Then just like many other things,
the best is right there in the middle.
If we take the good things about
>> symmetric cryptography and combine them
>> with the good things about asymmetric cryptography,
>> we have a hybrid cryptography,
which is what most applications
>> and secure protocols use.
>> Then we're going to move on to talking about integrity.
One of the ways we get integrity is through hashing.
Hashing will create a digital representation of a file.
You can also take that hash and add
authenticity to it and get non-repudiation.
Non-repudiation is a combination of
authenticity and integrity together.
If we think about that with an email,
the sender can't dispute having sent
the message nor the content of the message.
Then you'll find out that a hash is very limited.
A public key infrastructure is
needed to support non-repudiation.
That takes a lot of support.
We may decide to use message authentication codes
or MACs to solve the problem instead.
MACs provide more security than hash.
You don't require as much support
and infrastructure as non-repudiation.
Now, Mac is one of
the most fun acronyms that is going
to mean something different every day.
But for this module,
the meaning is message authentication code.
Last but not least, we're going to
talk about some email cryptosystems.
We'll talk about PGP,
which is proprietary cryptosystem.
Then we'll talk about S/MIME.
This is a long chapter and I
hope you find it as interesting as I do.
Now, starting with the basics as promised,
the first thing I want to talk about is
what cryptography does for us.
Most people would say that we need cryptography
because we need privacy and
>> we want to protect our data.
>> But in addition to privacy,
we also get authenticity, integrity,
>> and non-repudiation.
>> Here's a quick overview of
the services that cryptography provides.
Privacy: Prevents
unauthorized disclosure of information.
Authenticity: Verifies the claimed identity.
Integrity: Detects modification of corruption.
Non-repudiation: Combines authenticity and integrity.
A sender can't dispute having sent
a message nor its contents.
If in doubt and you can't think of
all the services that cryptography provides,
think of PAIN: privacy,
authenticity, integrity, non-repudiation.