# Algorithms and Keys

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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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We already talked about are

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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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>> your image, or your data is,

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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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but it is very helpful.

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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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