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All right, without wasting any much time around cryptography, let us get started with the most of



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the topic of symmetric encryption and asymmetric encryption.



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So what is cryptography is you encrypt data, you pass the encrypted text and decipher text, and then



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you decrypt the data.



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OK, so now there are two major types of encryption that we are going to see, symmetric encryption



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and asymmetric encryption.



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So let us consider that you have this document over here and this is very confidential, okay?



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It has some sort of statistics that only you want, that only your boss wants to know.



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You don't want to leak any confidential information.



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So what you do is you lock this document, okay?



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You lock this document with a key.



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Now, remember, now this is the key which we have used in order to encrypt this data.



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So when you encrypt this document, it is locked.



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OK, so this is the lock for what you do is you transfer, you encrypt, and it gives you an encrypted



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document, a cipher document.



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You can call this as a text encrypted with one key.



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It is known as a ciphertext.



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Now, what you do is you pass over the ciphertext and once you pass the ciphertext, the if you if someone



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wants to read this ciphertext, they will only read some gibberish characters.



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They won't know what they've actually done.



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And that is the encryption algorithm.



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We are going to see different types of encryption algorithm.



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We are also going to see some live conversions and encryption.



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So just remember that when you take a plain text and you encrypted with a key, it gives you a cipher



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text.



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So now you have the ciphertext.



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But how are you going to decrypt the ciphertext?



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Well, in the same way, consider this situation as this is your house and you know what's inside the



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house.



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You know what is inside your own house.



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You know where your wardrobe is, where your kitchen is, where your money is in the house.



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Now, let's consider your going out on a business trip and you don't want anyone to enter your house.



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Well, every one of us wish the same.



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Now, what you do is you lock your house with a lock and you have the key.



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So this is a locked house.



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This is your locked house.



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Now, when you return, you have the key you unlock and then you get the original documents.



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So you get into your house and you can see that this is the same key that we had used to lock and we



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have also used to unlock.



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And that is why the name is symmetric encryption.



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Only one key is used to encrypt, that is to lock.



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And the same key is then used to decrypt, that is unlock.



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So this is known as symmetric encryption, where you use one key to unlock or lock the message and you



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use the same key to unlock so that there is no other thing.



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You just lock and unlock the box.



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If you want to remember asymmetric encryption, remember that you have your house, you're going on



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a vacation, you lock your house, you come back, you unlock your house with the same key and that



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is symmetric encryption.



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And that is another type of encryption, which is asymmetric encryption.



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So let us see how many keys are used in asymmetric encryption.



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So let us have a look at asymmetric encryption.



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Again, this is the original plain text.



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This is the key.



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You have encrypted this document to give you the ciphertext now, since this is asymmetric encryption,



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what are you going to do is you have another key here, then you unlock and you get the original document.



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So what's the exact difference?



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Well, you locked with this key, the first key, and then you unlocked with this key.



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That is the second key.



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So here in asymmetric encryption, two keys are used in order to encrypt and decrypt.



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Well, you can also encrypt with this black key here and you can also decrypt this key.



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But what you need to understand is you need to have two different keys.



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Again, if you want to visualize this example, let's say you are going on a business trip and right



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now your wife is at the office and you have to go urgently.



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You have a plane to catch and you don't know what to do.



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So what you do is you have a copy of your keys so that even if you lock with the key, you have your



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wife can unlock your house with the key she has.



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So in that way you can walk and therefore you have to keys.



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And it is asymmetric encryption.



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You lock with one key and then you unlock the text with a different key.



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In cryptographic world, these two keys are known as public and private keys.



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So you can either encrypt with the public key and then decrypt with the private key, or you can encrypt



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with the private key and then decrypt with the public.



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You will have a question.



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OK, if there are two methods, which one is the most secure?



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Well, I want you to think over this because we are going to see asymmetric encryption in later part



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of this course.



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But if you are curious, I would like to give I would like to give you, let's say, two to three days



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if you want, or two to three lectures to think so.



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Stress on this point.



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If we can encrypt with private key as well as public key, which key will you use?



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And I would like to give you a hint that public key is public knowledge, which is it is available to



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everyone.



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So now, while we are going to study about asymmetric encryption, those who have this question, keep



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your answer ready.



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The first option is you can encrypt with private key and then decrypt it public.



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Or the second option is you can encrypt with public key and decrypt it private.



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So this lecture was about two types of encryption, symmetric encryption and asymmetric encryption in



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the device.



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So you have this one guy over here, these two guys are saying, OK, I'll just erase everything.



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Yes.



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No, it's perfect.



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So when it comes to asymmetric encryption, you had two keys here.



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You had two keys, but the keys were exactly the same because you use the exact same keys to encrypt



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the message and decrypt the message.



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But when it came to us asymmetric encryption, you had two different keys to encrypt and decrypt.



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I hope this lecture was pretty clear.



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This is just a high level idea.



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We have not yet dive into the deep of symmetric and asymmetric encryption, but in the next lecture



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we are going to talk about different types of ciphers which are used in modern cryptography.



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I will see you in the next lecture.