-: Unlike symmetric algorithms,
asymmetric algorithms do not require a shared secret key.
For this reason, we often refer to these
as public key cryptography.
With asymmetric algorithms,
we use a key pair to encrypt and decrypt the data.
These two keys, are called the public key
and the private key.
Now, public key cryptography can provide us
with confidentiality, integrity,
authentication and non-repudiation
for the messages being sent.
To provide confidentiality of the data,
the data should be encrypted,
using the receiver's public key.
So, if I wanted to send a document to Mary,
as you could see here on the screen,
I would encrypt that document
using Mary's public key.
By doing so, only Mary is able to read it,
because only Mary is going to have Mary's private key.
And this is going to be used to decrypt the contents,
ensuring that the message I sent,
is safe from anybody else's prying eyes.
Now, once I encrypt the data that I'm sending to Mary,
using her public key, no one can read it, except Mary.
Even me, the sender, I'm not able
to decrypt that information.
It's a one way encryption, when I use a public key,
and only the private key can decrypt it back out
to readable text.
Now, to provide non-repudiation,
the message should be encrypted using the sender's
private key, so in this case, I would use my private key.
By doing so, anyone who has access
to the sender's public key, which could be anyone
in the world, is going to be able to open that message,
and read it.
This isn't going to give us any kind of confidentiality,
but I'm not worried about confidentiality right now.
Instead, I'm worried about making people know
I'm really the person who send the message.
That's the non-repudiation we're working at.
This is going to make sure that only I can send it,
because only I have my private key.
Now, in most organizations,
we don't want just confidentiality,
or just non-repudiation.
We want both of those things.
And we also want to add to that list,
we want integrity, and we want authentication
to make sure we have this message being sent
where nobody else can read it,
and we know who it came from,
and that it was never changed in transit.
To accomplish all of this with our emails,
we often implement a process
to create a hash digest based on the message being sent,
and then we encrypt that hash digest,
using the sender's private key.
This is known as a digital signature,
and it provides us with the integrity
of the message that's being sent,
as well as giving us non-repudiation,
because only the sender had access to their private key.
Then, we take the message we're sending,
and we encrypt that using the receiver's public key.
This provides us confidentiality as well.
So now I've got integrity of the message,
non-repudiation, as well as confidentiality.
To make this whole system of public and private keys
work smoothly, there's another concept,
that we're going to cover in a future section,
called public key infrastructure, or PKI.
I'm dedicating the entire next section of this course,
to the concept of PKI.
So, for right now, if the idea of public key cryptography
doesn't quite make sense yet, don't worry,
it soon will, as we go through several examples,
to make sure you get it.
For right now, I just need you
to remember a couple of things
about asymmetric encryption.
First, asymmetric encryption is known
as public key cryptography.
And, second, public key cryptography
uses two keys for each message.
One key is used to encrypt it,
and a separate key is used to decrypt it.
(digital buzzing)