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