I told my girlfriend you can’t do this to me. She told me I won’t accept or send any letter anymore. I used to send her a letter via her friend and she did the same. But after a few days her friend started reading our letter and started teasing her. So I started adding 2 indexes in every alphabet letter (I write a as c, b as d, c as e and so on) sometimes I add 2 sometimes 4 sometimes any number and I used to write that number on that letter too and she did the same. But after a few days her friend cracked that too and she got to know that we are writing keys on letters her friend used to decode. Then we were stuck on what to do now. Then I found one more way there in the market. There was a pair of (Pen and Spectacle ) If you write anything with that pen so a person who has that Spectacle can see the text written. So we bought two pairs and exchanged pens with each other. Now we can clearly and without any problem we can communicate with each other.
The first mode of communication is called symmetric cryptography where a single key is shared between two parties, the same key is used to encrypt and decrypt.
Symmetric Methods are AES, DES.
The second mode of encryption is called asymmetric cryptography in which public key, private keys are used. A public key is used to encrypt the data and the person who will have a private key will be able to read the message.
Asymmetric Methods are RSA, ECC.