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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