# Symmetric vs. Asymmetric Review

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Time

15 hours 43 minutes

Difficulty

Advanced

CEU/CPE

16

Video Transcription

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>> Let's continue our discussion on

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symmetric versus asymmetric cryptography

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because I think this is something that you really

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want to be solid on before you move on,

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before you go into SSL or

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IPsec or any of those other implementations.

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Symmetric cryptography,

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when we look at cryptography as a whole,

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we have these two basic types.

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We have symmetric and we have asymmetric.

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When we look at the symmetric algorithms, remember,

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symmetric algorithms are fast

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and we want to use them to encrypt our bulk data.

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But we had some of those drawbacks that we talked

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about, out-of-band key exchange.

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We had the problems of not being able

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to get authenticity and integrity.

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We had the problem of key distribution.

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We had all these problems, but

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we said because it's fast,

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we really want to use it.

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Now, symmetric ciphers can either be stream or block.

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Stream encrypts bit by bit.

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Remember that process of exoring that we looked at.

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Stream ciphers are very fast,

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but they're less secure.

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The vast majority, as a matter of fact,

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everything except RC-4 that

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was symmetric that we looked at,

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they were block algorithms or block ciphers.

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The most common was and is AES.

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That's the current standard that the government uses to

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protect sensitive, but unclassified information.

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It's the de facto standard for

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the vast majority of applications.

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DES and then Triple DES were the predecessors to AES.

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Now, whenever you're in doubt,

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when you get a question that says,

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which encryption algorithm is used to?

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If you don't know the answer,

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you should probably guess AES because that's

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just the de facto standard for most algorithms.

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Which encryption algorithm is used to

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protect communications in a carburized environment?

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Yes. When in doubt, go with AES.

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There's one exception though.

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There's an email application

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called Pretty Good Privacy, PGP.

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It came to us from Phil Zimmermann.

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Phil Zimmermann was a big advocate

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for privacy and still is.

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The idea that Zimmermann had was look,

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most of the algorithms that we're using come

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from the government or they are

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based on government standards.

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Knowing that the government would like to

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be able to decrypt anything encrypted,

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why would we use

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standards that are blessed by the government?

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In his thought was maybe

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the government has a backdoor into those algorithms.

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Zimmermann created

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his own proprietary email application called PGP.

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He created a proprietary algorithm called IDEA,

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which stands for Internet Data Exchange Algorithm.

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I want you to guess AES when you don't know the answer.

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But if the question is about PGP,

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it used the algorithm IDEA.

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[NOISE] That's the symmetric side

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of things over on the asymmetric side.

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Asymmetric algorithms use factorization

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or a math function called

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discrete logarithms in a finite field.

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That's a big heavy discussion for another day.

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Almost all of them use discrete logarithms.

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The exception to that,

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if you'll remember, was RSA.

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RSA, the relationship between the keys is

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based on the idea that

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it's very easy to multiply

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two really large prime numbers together,

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but it's incredibly difficult to

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factor out what numbers were used.

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That's the relationship with the keys.

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The others use this concept of discrete logarithms.

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We're not going to go into that in this class.

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But Diffie-Hellman and ECC and

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ElGamal, everything but RSA.

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Again, just a last little chart that's a wrap up.

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You may want to do a screen capture here just so that

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you have this and make sure that you're solid on,

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how keys are addressed,

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where the performance issues are,

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how many keys are necessary or

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would be needed in each environment.

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This is a good wrap up.

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We just wanted to roll

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everything together and make sure we have

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an understanding of the way symmetric algorithms

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work versus the way asymmetric algorithms work

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