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Now we're going to see an interesting protocol that is a pretty good privacy, as the name suggests,

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an excellent protocol, and the walking is very simple to understand.

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If you have understood the previous cryptography and the public key encryption decryption videos, then

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this lecture is going to be a wonderful lecture for you.

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Now, in this lecture, I am not going to have any bullet points.

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I'm just going to explain through the slides.

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So in the early 1990s, Phil Zimmermann, also from M.I.T., that is Massachusetts Institute of Technology

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and US, wrote most of the code for his freely available version of public key encryption designed to

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encrypt data for email transmission.

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PGP is mostly used for email transmission.

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Make sure you remember that Zimmerman basically compared email to postcards because anyone can read

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e-mail messages traversing the Internet just as they can.

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Postcards traveling to the Postal Service.

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Right by contrasting, he compared an encrypted message to a letter mailed inside an envelope.

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And this is the figure of PGP encryption system.

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So don't worry.

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I'm going to explain what exactly is now in the figure or you can see on the screen.

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Let me take my pen.

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Yes.

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So the document this is the original document.

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OK, now the document is encrypted with a session key.

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So let's consider this is a session key, OK, which is then encrypted with the public key of the recipient.

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So let's see.

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Here is the recipient and his public key is available in this key store because public is a public knowledge.

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It is available to everyone.

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Now with this public key.

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This key is encrypted because we know that whenever you want to send a data over the Internet in order

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for the recipient to decrypt the data with his private key, you must encrypt the data with the public

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key and then only the public or the private can decrypted.

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OK, so now this session is encrypted with the public key of the recipient and this data is also encrypted

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with the session key.

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And then the encrypted document, along with the encrypted session key with the help of public key is

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sent over to the recipient here.

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OK, I'll erase it so that you will have a clear picture of.

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Oh, yes.

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Now, let's see how do we explain the decryption process?

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So once again, I will revise the encryption process, you have the document, you have a session with

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the help of session key, you encrypt that document and then you end this session with the help of the

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public and then this encrypted document, plus encrypted session key.

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You sent it over to the recipient here.

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Now, when the recipient receives the encrypted document along with the encrypted session key, now,

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since this session key is encrypted with the public key of this recipient, it can be easily decrypted

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with the help of private keys of the recipient.

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So when the recipient decrypt the encrypted key with his private key, he gets the original session

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key.

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He gets the audience session key.

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And with the help of this session key, he then decrypt this document to form the new document to get

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the original document.

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So in this case, what you have to remember is session key encryption is done using symmetric encryption.

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That is the same key for encryption and the same key for decryption.

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But in order to transfer the session key over the Internet, automatic encryption is used.

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Now, automatic encryption takes a longer time than symmetric encryption.

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That is why in order to just transfer the keys, asymmetric encryption is used in most of the today's

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world.

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But when it comes to encrypting local documents or the symmetric key, encryption is used.

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So make sure you remember this is the example of pretty good privacy.

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OK.

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Now, since the recipient is the only person with the matching private key on the deck and decrypted

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session, because there we are using asymmetric key, uh, encryption, uh, for the personal use only.

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And the name implies it's really pretty good privacy.

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RNC data security that is reversed.

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Shamir and Adelman security and the US federal government both had a problem with Zimmermann's product.

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Now, the RNC complained about patent infringement and the government actually decided to prosecute

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Zimmerman for exporting munitions, great software.

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But the government actually dropped the charges against Zimmerman and the licensing fee is paid to Oddisee.

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So today, BGB and other public utility products are readily available.

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But if you cleverly see this is the most of it actually is a good protocol for encryption and preventing

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your data over the direct transfer.

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I hope my lectures are very clear to you because I'm trying to explain all those things in very simple

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and clear words.

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So if you're really enjoying this course, I request you to read Arcus, because if you read articles,

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So please read our your feedback is very valuable to us.

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I will see you in the next lecture.