- [Instructor] Cryptography is one of the
most important controls available to
information security professionals.
Encryption protects sensitive information
from unauthorized disclosure
in many different environments.
And many other security functions
depend upon cryptography to function properly.
So, what is cryptography?
Cryptography is the use of mathematical algorithms
to transform information into a form
that is not readable by unauthorized individuals.
Cryptography does, however,
provide authorized individuals with
the ability to transform that
encrypted information
back into readable form.
Cryptography depends upon two basic operations.
The first, encryption,
converts information from its plaintext form
into an encrypted version
that is unreadable.
This is known as ciphertext.
The second operation, decryption,
performs the reverse transformation.
Using an algorithm to transform that
encrypted ciphertext
back into plaintext format.
I've used the term algorithm a couple of times.
If you're not already familiar with algorithms,
they are simply a set of mathematical instructions
that one follows to achieve a desired result.
Think of an algorithm as a mathematical recipe.
Algorithms are very similar to computer code,
and in fact, computer code is often designed
to implement mathematical algorithms.
Let's take a look at a basic algorithm
designed to convert temperatures
from Fahrenheit into Celsius.
The algorithm has an input.
The temperature in Fahrenheit.
And then it takes that input through a
series of steps.
First, it subtracts 32 from the input,
then multiplies the result by 5,
and divides that result by 9.
This provides us with the output,
the final result, which is the Celsius equivalent
of the temperature that was input in Fahrenheit.
Encryption algorithms work in similar ways,
except the steps are a little different.
Encryption algorithms have two inputs.
The first is P, the plaintext message.
And the second is K, the encryption key.
They then go through a series of steps
that transform the plaintext using the key.
I'll skip over the details of how encryption algorithms
work for now, because we'll be discussing them
extensively during the rest of this course.
The encryption algorithm then has
a single output, C, the cipher text.
Decryption algorithms perform the reverse operation.
They also have two inputs, the ciphertext message
and the decryption key.
And they go through a series of steps
that convert the ciphertext
into plaintext using that decryption key.
And then they return the
plaintext message as output.
Encryption and decryption are the
two basic concepts of cryptography.
I'm going to fill in the details
throughout the rest of this course.
You'll see how different cryptographic algorithms
use different steps,
and learn more about the roles of
different types of cryptographic keys.