All right, without wasting any much time around cryptography, let us get started with the most of
the topic of symmetric encryption and asymmetric encryption.
So what is cryptography is you encrypt data, you pass the encrypted text and decipher text, and then
you decrypt the data.
OK, so now there are two major types of encryption that we are going to see, symmetric encryption
and asymmetric encryption.
So let us consider that you have this document over here and this is very confidential, okay?
It has some sort of statistics that only you want, that only your boss wants to know.
You don't want to leak any confidential information.
So what you do is you lock this document, okay?
You lock this document with a key.
Now, remember, now this is the key which we have used in order to encrypt this data.
So when you encrypt this document, it is locked.
OK, so this is the lock for what you do is you transfer, you encrypt, and it gives you an encrypted
document, a cipher document.
You can call this as a text encrypted with one key.
It is known as a ciphertext.
Now, what you do is you pass over the ciphertext and once you pass the ciphertext, the if you if someone
wants to read this ciphertext, they will only read some gibberish characters.
They won't know what they've actually done.
And that is the encryption algorithm.
We are going to see different types of encryption algorithm.
We are also going to see some live conversions and encryption.
So just remember that when you take a plain text and you encrypted with a key, it gives you a cipher
text.
So now you have the ciphertext.
But how are you going to decrypt the ciphertext?
Well, in the same way, consider this situation as this is your house and you know what's inside the
house.
You know what is inside your own house.
You know where your wardrobe is, where your kitchen is, where your money is in the house.
Now, let's consider your going out on a business trip and you don't want anyone to enter your house.
Well, every one of us wish the same.
Now, what you do is you lock your house with a lock and you have the key.
So this is a locked house.
This is your locked house.
Now, when you return, you have the key you unlock and then you get the original documents.
So you get into your house and you can see that this is the same key that we had used to lock and we
have also used to unlock.
And that is why the name is symmetric encryption.
Only one key is used to encrypt, that is to lock.
And the same key is then used to decrypt, that is unlock.
So this is known as symmetric encryption, where you use one key to unlock or lock the message and you
use the same key to unlock so that there is no other thing.
You just lock and unlock the box.
If you want to remember asymmetric encryption, remember that you have your house, you're going on
a vacation, you lock your house, you come back, you unlock your house with the same key and that
is symmetric encryption.
And that is another type of encryption, which is asymmetric encryption.
So let us see how many keys are used in asymmetric encryption.
So let us have a look at asymmetric encryption.
Again, this is the original plain text.
This is the key.
You have encrypted this document to give you the ciphertext now, since this is asymmetric encryption,
what are you going to do is you have another key here, then you unlock and you get the original document.
So what's the exact difference?
Well, you locked with this key, the first key, and then you unlocked with this key.
That is the second key.
So here in asymmetric encryption, two keys are used in order to encrypt and decrypt.
Well, you can also encrypt with this black key here and you can also decrypt this key.
But what you need to understand is you need to have two different keys.
Again, if you want to visualize this example, let's say you are going on a business trip and right
now your wife is at the office and you have to go urgently.
You have a plane to catch and you don't know what to do.
So what you do is you have a copy of your keys so that even if you lock with the key, you have your
wife can unlock your house with the key she has.
So in that way you can walk and therefore you have to keys.
And it is asymmetric encryption.
You lock with one key and then you unlock the text with a different key.
In cryptographic world, these two keys are known as public and private keys.
So you can either encrypt with the public key and then decrypt with the private key, or you can encrypt
with the private key and then decrypt with the public.
You will have a question.
OK, if there are two methods, which one is the most secure?
Well, I want you to think over this because we are going to see asymmetric encryption in later part
of this course.
But if you are curious, I would like to give I would like to give you, let's say, two to three days
if you want, or two to three lectures to think so.
Stress on this point.
If we can encrypt with private key as well as public key, which key will you use?
And I would like to give you a hint that public key is public knowledge, which is it is available to
everyone.
So now, while we are going to study about asymmetric encryption, those who have this question, keep
your answer ready.
The first option is you can encrypt with private key and then decrypt it public.
Or the second option is you can encrypt with public key and decrypt it private.
So this lecture was about two types of encryption, symmetric encryption and asymmetric encryption in
the device.
So you have this one guy over here, these two guys are saying, OK, I'll just erase everything.
Yes.
No, it's perfect.
So when it comes to asymmetric encryption, you had two keys here.
You had two keys, but the keys were exactly the same because you use the exact same keys to encrypt
the message and decrypt the message.
But when it came to us asymmetric encryption, you had two different keys to encrypt and decrypt.
I hope this lecture was pretty clear.
This is just a high level idea.
We have not yet dive into the deep of symmetric and asymmetric encryption, but in the next lecture
we are going to talk about different types of ciphers which are used in modern cryptography.
I will see you in the next lecture.