Public Key – Secrecy

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Del curso dictado por New York University Tandon School of Engineering

Cyber Attack Countermeasures

202 calificaciones

New York University Tandon School of Engineering

Cyber Attack Countermeasures

202 calificaciones

Curso 2 de 4 en SpecializationIntroduction to Cyber Security

This course introduces the basics of cyber defense starting with foundational models such as Bell-LaPadula and information flow frameworks. These underlying policy enforcements mechanisms help introduce basic functional protections, starting with authentication methods. Learners will be introduced to a series of different authentication solutions and protocols, including RSA SecureID and Kerberos, in the context of a canonical schema. The basics of cryptography are also introduced with attention to conventional block ciphers as well as public key cryptography. Important cryptographic techniques such as cipher block chaining and triple-DES are explained. Modern certification authority-based cryptographic support is also discussed and shown to provide basis for secure e-commerce using Secure Sockets Layer (SSL) schemes.

De la lección

Overview of Public Key Cryptographic Methods

This module introduces the basics of public key cryptography including an overview of SSL and CA applications.

Assignments and Reading2:56

CBC Mode Block Cryptography4:53

Conventional Cryptography Scaling Issues4:47

Public Key Crypto (Basics)5:10

Public Key – Secrecy4:31

Public Key – Digital Signature3:28

Cryptographic Message Exchange5:39

Diffie-Hellman Key Exchange7:32

Key Distribution and Certification Authority10:04

Secure Sockets Layer6:56

The Story of James Ellis and Clifford Cox10:06

Welcome Franscis Cianfrocca16:46

Conoce a los instructores

Dr. Edward G. Amoroso
Research Professor, NYU and CEO, TAG Cyber LLC
Computer Science

Hi, folks, in this video, we're going to take some time and

look at the way public key cryptography can be used to send a secret message.

So we're going to start playing with the concepts of Diffie and Hellman.

And you recall in previous video, we said that Alice and Bob, or

whose sender or receiver, are in some sense doing something locally to

generate their key pair, there's no key distribution center.

And the key pairs are set up such that encrypt with secret,

decrypt with public and so on.

So let's assume, and we'll pop up a little chart here that shows Alice and

Bob and is their pre-condition, we'll list out what they have,

what they know, or what they've been setup with.

And the setting up is called infrastructure and for public key it's

called public key infrastructure, PKI, which you may have heard of.

Tends to be a lot of work to set up PKI for a typical setting.

But for now let's assume Alice is going to have both a public and secret key pair

which Alice generated locally, pushed the button, ran the RSA algorithm, boom!

Pair pops up, PA, SA.

But she also has the public key of Bob because we're going to

make the assumption that everybody knows everybody else's public key.

Is that fair enough?

Similarly Bob, what does Bob do?

Runs an algorithm locally, generates PB, SB, has that key pair.

He didn't have to go to a key distribution center, for he did it locally.

But also has PA, has Alice's public key.

Everybody's got everybody's public key.

And we can throw Eve in there too, Eve is the eavesdropper.

I don't care what Eve's public key pair is.

Yeah, she generates her own key pair, but who cares?

But she does know PA and she does know PB, fair enough?

That's the precondition.

Now, what I'm going to do is Alice is going to encrypt a message.

And what are the things she can encrypt with?

Well, there's PA, SA, PB.

Let's encrypt with PB.

Let's see what happens when I encrypt something with the public key of

the recipient.

When I do that, the message goes across to Bob.

And when it gets to Bob, Bob can decrypt it because Bob has the secret key.

But let's think about Eve in the middle of this.

Can Eve read an encrypted message and using public key of B.

Well. what needs to be present to decrypt it?

SB, Bob has that, Eve does not.

Eve can't read the message.

So the message is like your credit card number, or something.

Then, in theory,

I can blast this across the whole internet to some online retail store.

The retail store gets the credit card number, nobody else can, fair enough?

So it's secret, but could Eve have somehow crafted this message?

Let's say it's not a credit card,

let's say it's a note asking Bob to do something.

Well, can Bob be confident that that was actually produced by Alice?

Well, what was the message using the public key of B?

Everybody's got the public key of B.

So do I have authenticity?

No!

So this is kind of interesting.

This shows that one of the options here, taking a message m and

having hours encrypted with the public key of the recipient makes it secret,

but does not respect authentication properties.

It doesn't prove that you are you.

Let's go back to credit cards.

If you send a credit card to a company, do they usually care who you are?

Well, it depends on the business, right?

[LAUGH] I think they probably do, but a lot of times they don't.

So this might be very useful protocol, but

what do we say about conventional cryptography?

We love that fact that we had secrecy and we had our Authentication, we liked that.

We didn't like if we lose one of those properties and

that's what's happened here.

So this is not going to do it, it's not acceptable.

You want secrecy and authentication.

So what can we do?

How can we solve this?

Well, for the answer, you'll have to wait for the next video.

I'll see you on the next one.

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