Algorithms and Keys

Video Activity
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Time
7 hours 50 minutes
Difficulty
Beginner
CEU/CPE
8
Video Transcription
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>> We're going to continue to build on this idea that
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>> if we take plain texts and an initialization vector,
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>> and an algorithm, and a key,
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we will somehow magically create ciphertext.
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>> what our initialization vector is.
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>> It's going to add randomness to the process.
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The next thing I want to talk about is an algorithm.
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Now if you see this screen,
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you can see that we've got a series of math functions.
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Base on my 12 years of
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North Carolina Public School math.
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The functions you see,
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>> are the only math functions I can perform.
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>> Now, I can take any number and add 2,
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subtract 2, multiply or divide by 2.
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I can raise the power of 2,
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take the square root of 2, but that's it.
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I can't do any other math.
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This is my algorithm.
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An algorithm is just the collection of
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math functions that can be performed.
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We have to remember that
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>> no matter how complex your message,
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it all comes down to numbers.
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It's just a series of zeros and ones.
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Some algorithms will take that data and
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chunk it into blocks of certain sizes.
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Somebody chunk it into 128-bit blocks.
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Each block goes through a series of math functions.
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With each math function, substitution happens.
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For example, when it goes through function 3,
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it gets to multiplied by 2,
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and the result of that is
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substituted for what you originally had.
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Each of these functions is where
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the actual substitution of cryptography happens.
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For that reason, sometimes
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instead of refrained to algorithms as functions,
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you'll hear them referred to as
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S boxes for substitution boxes.
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But this is where the actual substitution
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happens in the algorithm.
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Now the problem is, I don't know
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how many functions we should
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use or the order we should use them.
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That is where our friend, the key comes in.
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A key is going to determine
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which functions are used and in what order,
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and how many overall math functions will be used.
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The key contains the instructions on how to use math.
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An algorithm and a key have to go together.
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Now, an initialization vector is not mandatory,
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A lot of times when we talk about how to encrypt,
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we do include the IV, algorithm, and key.
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But honestly,
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>> if you only had the algorithm and the key,
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>> you still have encryption.
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I will also say for future discussions
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that when I say algorithm,
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I could also just say cipher.
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Those two words are really interchangeable.
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Now, key is much more frequently used term,
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but an alternative to a key would be a cryptovariable.
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But I will probably never say
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that. I will always say key.
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