Hey Guys, this is Ram here from 
EngineeringMentor.com
In this video, we will talk about some of the basics of cryptography
like what is cryptography and why do we need it etc.
After that we will discuss the traditional cryptography model
which is based on encryption and decryption of messages.
So let's start.
When we are talking about communication over a network
we need to make sure that there is some sort of security
for the information being communicated.
Now a question might pop up in your mind 
as to why do we need this security during transmission?
Let me explain this with an example.
Suppose you are shopping online with your laptop
and you use your credit card for payments. 
At this time your credit card information is sent to the server for verification. 
Now the server at the end of this line
might provide security for your information
 when the information is within the server.
But what about the time when it is under transmission? 
If there is no security here, the information is vulnerable. 
A hacker might easily tap out your credit card information
and empty your pockets!
You wouldn't want that, do you? 
So the information needs to be protected when it is travelling through the network.
If you just think about the things you do over the internet
it is easy to point out many such examples where you need security.
Whether it is sending personal emails
or any web transactions
or confidential information being 
transmitted between military organizations
everywhere SECURITY is an important requirement!
So how do we provide this security during transmission then?
Well, One way of ensuring security can be use of CRYPTOGRAPHY
Cryptography is a field of network security
which deals with hiding "real" infromation
when it is under transmission between two parties.
Usually, the real information is transformed
or hidden into another message and transmitted over the network.
This transformed message in itself will make no sense
even if any hacker gets hold of this information. 
When it reaches the destination
the reciepent will know a method to de-transform
the garbage message into its original message
which was sent by the Sender
I will give you a simple Example.
Let us say a boy Bob wants to send a message
"I love you" to his girlfriend Alice
Now he wouldnt want anyone else to see this message
Let us say he uses a software to convert the message
 into some numbers say "143"
and this software is available is only with Alice and Bob and nobody else
Now 143 is sent across the network to Alice
If a hacker gets hold of this message 143
he will not be able to guess what is the real information 
because he does not have this conversion software
So the real information is safe
When the message reaches Alice, 
she will use the same software
to convert 143 to real message, "I love you"
And she will be happy seeing the message,won't she!
So this method of transforming message at sender's side
and de transforming at reciever's side
forms the basic model of Cryptography.
Converting real information into what looks like garbage value
this process is called as Encryption
meaning to say you are hiding or locking the real information into some other form
And the process of extracting real information back from this meaningless text
is called as Decryption
meaning to say we are unlocking 
or extracting the original message that was sent
Let us now see this cryptography model a little more technically.
So this is the skeletion of the model
Let us define it more clearly
First, the information to be transmitted
is called as plain text(or message)
is fed to an Encryption system
The Encyrption system uses a key to convert the plain text to encyrpted form
which looks like garbage value
This is also called as cipher text
A corresponding key is used at the other end
to decrypt the cipher text back to original message
When we say a "key"
it actually means a piece of string value
which is fed to encyprtion and decryption algorithms
along with the text for transformation
This is similar to locking your valuable things in a box
and sending it across
At the other end the reciever will use the secret key
to open the box and read the message you (Sender) sent.
If a hacker were to tap out the message being transmitted in the network
he will get the encrypted message, say "143"
Now he will not have the key to decrypt this message
so this cipher text will not mean anything to him
He may try to use several methods to break this code
and get the hidden message out of this
This art of trying to break ciphers forms a different branch of study
called as Cryptanalysis
but we will not go into that right now
This Encrption and Decryption together ensure security of the message
being transmitted across the network
This whole encryption and decryption strategy
is based on the premise that
both sender and reciever share some unique keys
which is not known by any outsiders, 
like the hackers.
Depending on how the keys are shared
we can classify crytography as 
Symmetric and Asymmetric
If the keys used by both parties are same
then it is called symmetric key cryptography
or private key cryptography
If both parties use different keys for encyrption and decryption
then it is called asymmetric key cryptography
or public key cryptography
We will stop it here for this video
In our next videos in cryptography series
we will discuss private and public key cryptography in detail
and also the various methods and algorithms
used under these to ensure security of messages.
