### Theory:

Teacher: "Is anyone here know how did our ancient Kings convey a message from the castle to their troops in a battle".

(The teacher observed the mumbling in the classroom. Then he saw one student raised a hand to speak).

Ramesh: "I think they could have used a secret language which does not make sense to the enemies".

Teacher: "Exactly, Ramesh. But they did not use any new languages. They used a usual language with a secret code which only they can understand".

(There is a slight sense of confusion in the classroom.)

Vinitha: "What is that secret code? How did they use it"?

Teacher: "Let me make it clear with an example. In an exam hall, Vinitha wants to convey something to Ramesh secretly. If she says it in a usual way, the examiner will catch her.

So, she says the word 'science' as 'tdjfodf' with the key is $$1$$. Knowing the key also the encrypted word, Ramesh decode the encrypted message to understand it.

Key $$1$$ refers to how many numbers the alphabet are shifted along with the letters. Since the key is $$1$$, the letters in the science are shifted to $$1$$ alphabet".

Ramesh: Wow, sounds interesting!

Vinitha: It seems exciting! But do we use this sort of coding in our daily life?

Teacher: "Excellent! question Vinitha. The study of the secure encrypted technique is called Cryptology. And Many countries used the encryption code in the World Wars to deliver a message.

Even in our digital world, we use this encryption technology in many situations, such as bank transaction and online encrypted conversation (what's app, Facebook), websites, and many more.

Now we all understand the basic idea of Cryptology, it is now time to dive into the concept more."

Fundamental technical details for Cryptology:
 Plain text The original message is called plain text. Cipher A set of rules that describes the process of converting the Cipher text into Cipher text. Cipher text or Cipher number The encrypted output (converted message into code) is called Cipher text or Cipher number.We usually write the Cipher text capital letters, and plain text in lowercase Key A secret key is to use something to generate the Cipher text from the plain text. Encryption and Decryption The process of converting the plain text to the Cipher text is called encryption and the vice versa is called decryption.

Reference:
https://www.shutterstock.com/image-vector/students-audience-young-people-sitting-tables-1206339283