Hello and welcome to this fundamentals of cryptography course and the previous two videos in this section,
we've been talking about the theory of symmetric creeky encryption.
We started out with a video talking about how symmetric encryption works and breaking it down into block
and stream ciphers.
After that, we'd looked at two of the more common symmetric encryption algorithms, A-S and our C4.
In this video.
We're going to be switching gears a little bit and start talking about how symmetric key cryptography
is used in the real world.
This first application is for bulk data transfer.
Every day we use the Internet and when we're using the Internet, we need to be certain that deep,
sensitive data that we provide, whether that's our credit card information, name and address, username
and password, etc, is securely transmitted over the wire.
Otherwise, there's a chance that someone who is able to eavesdrop on our traffic could potentially
learn information about us.
We don't really want to share.
And so symmetric key encryption is essential for transferring this data securely over the Internet.
And so in this discussion, we're going to start out with a talking about the need for secure data transfer.
Essentially the why, followed by talking about why symmetric key encryption is used for data transfer
and why symmetric cryptography is not enough for data transfer on its own.
Finally, we'll talk about secure sockets, layer SSL and transport layer security tearless, which
are two iterations of the same protocol designed to actually implement secure data transfer on the Internet.
And so why do we need secure data transfer?
Many of the Internet protocols that we use today were not designed for security.
In fact, data is commonly transferred unencrypted over the Internet.
And these protocols you probably heard of the difference between HTP and HTP s whether or not you have
that lock icon in your browser.
Well, the difference between those is HTP is fully unencrypted.
It's the original protocol and HTP s is encrypted, meaning no one can eavesdrop on that.
And the actual protocol used to transfer the data over the Internet.
HTP doesn't really change between the two.
The difference is the fact that for a a CPS, we use an encapsulating protocol to provide security.
Originally this was called the Secure Sockets layer and later versions transition to the named transport
layer security.
And what these do is they wrap around the base protocol, whether that's HTP or some other protocol,
and provide the encryption and data security that the original protocol lacks.
And so symmetric cryptography is actually extremely useful for data transfer.
It has a number of different advantages if you want to securely transfer bulk or large amounts of data.
One of these is the fact that symmetric encryption is usually more efficient than asymmetric cryptography.
If you're using public key cryptography, typically it'll take longer and produce safer texts that are
larger than the equivalent produced by symmetric encryption.
And so while maybe sending a short message encrypted doesn't really matter.
Sighs If you're getting into much larger messages, think gigabytes or terabytes than that little bit
of additional overhead can make a big difference on how quickly you can download that file or send something
to someone else over the Internet.
Another advantage of symmetric encryption for bulk data transfer is that some of those blocks, safer
modes of operation.
We've talked about previously allow you to decrypt multiple blocks in parallel, for example, ECB mode.
We looked at it previously and talked about how it's insecure.
But one of the advantages is parallel decryption.
If every single chunk of data is encrypted and decrypted completely independently, there's no reason
you can't decrypt four or five or a thousand of them all at the same time.
While with other modes of operation or with asymmetric cryptography, you may need to do everything
sequentially, which is slower.
And so with this ability to paralyze, decryption things can go more quickly on multicore processors,
which is a huge advantage when you're transferring large chunks of data over the Internet.
However, while symmetric cryptography is useful for bulk data transfer, it's not enough on its own.
And the reason why is that symmetric encryption so we've talked about requires a shared secret key and
that shared secret key needs to be shared over a secure channel.
And so with the Internet, it could be difficult to establish a secure channel.
And.
When you need a secure channel, you can't talk to someone you've never talked to before.
If we only use symmetric encryption for data transfer over the Internet, you'd only be able to visit
Web sites securely if you'd already set up a shared secret in advance, which could be difficult or
impossible.
In reality.
And so as a result, in most cases, secure bulk data transfer is going to require asymmetric cryptography
to setup that shared secret key.
And we're gonna talk about that more in a later section of this course where we talk about asymmetric
cryptography and especially for key exchange.
And so symmetric cryptography isn't enough.
We need both symmetric and asymmetric cryptography for secure data transfer.
And so when we're using SSL A.l s to make communications on the Internet secure, we're wrapping broda
calls that are insecure by default in encryption, authentication, et cetera, to ensure that they're
protected when traveling over the untrusted Internet and SSL and tearless require all three types of
cryptographic algorithms to really work properly.
We're going to use asymmetric encryption for the key exchange because we can establish a shared secret
key over an untrusted network in a secure way using asymmetric encryption.
We're going to use symmetric encryption for the bulk data transfer because it's more efficient than
asymmetric encryption.
We could certainly do everything with public key encryption, asymmetric encryption, but efficiency
is important.
And finally, we're going to use hash functions to protect the integrity of the message, we need to
make sure that we don't have any errors in the cipher text that we receive at the other end.
We talked about bit flipping attacks in the previous video.
Those are a potential threat for our C4 and other stream ciphers.
Or there's the potential that a bit could be flipped simply by accident.
There can be encoding and transmission errors as data flows over the Internet.
And if one of those occurs and something goes wrong, we need to know.
So we're using hash functions as well.
So every single day when you're using the Internet and using T for secure data transfer, you're using
every type of cryptography that we're talking about in this course.
And so, as a recap, secure data transfers necessary.
Do you want to be able to shop at an e-commerce site like Amazon?
You need to make sure that your order data, your payment card information, etc is securely transmitted
symmetric.
Key encryption is important for this, but it's not enough.
We also need asymmetric cryptography and hash functions to make everything work.
And so this is one potential use case of symmetric key encryption that we see every single day.
And then next video, we'll talk about another application of particularly symmetric cryptography that
you may also be using in everyday life.
Thank you.