cryptography basic part II

CRYPTOGRAPHIC BASICS PART II

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In earlier article we learnt about functions .
today we will be messing our hands in real stuff,encryption with primitive methods
The one not following my cryptography posts reading for first time must took a glance at older posts by the link given below
cryptographic-basics-part-i
Basically encrypyion and decyption is done by the use of a key,which is designed by encryptor to encrypt it.
Basically key is divided in two broader categories

• Symmetric key
• Public Key

In this article we will focus on symmetric keys
Symmetric keys have been used ancient times so it has a wide history,Ancient greeks ,ancient egyptians used it,But the most recognised incident is the use of symmetric keys by nazis during world war II with the help of Enigma machine,Enigma was considered as an uncrackable machine.Had not been there the great cryptanalyst Alan Turing,British would have suffered a lot.

Symmetric key:the key used for encryption and decryption is same rhe actual text and ciphered text are easily convertble function. Once a cryptanalyst knew the original key used for encrypting the text he could easily decrypt the ciphered text.therefore the key used should be kept secret and passed through secured channel while the ciphered text could easily passed through unsecured channel.

Symmetric Keys too are classified in two other broader categories

• Block ciphers
• Stream ciphers

Block ciphers : these ciphers encode the text to a block of fixed length and then precede according to key

here we will discuss only substituted block ciphers
there are two kinds of substituted ciphers:

• monosubstituted cipher
• polysubstituted cipher

Monosubstituted cipher:this encode using a single pattern for key,for example:
let us encode the text according to monosubstituted block cipher
Our text is "WELCOME TO FREE LEARN HACKING"
we will follow the steps:

1. first make block of fixed length for text say 5
   then our text will become WELCO METOF REELE AENHA CKING
2. now comes the crucial step deciding the key,let us decide the key as replace each alphabet with their second successor like A from C
   now our text we look like YGNEQ OGVQH TGGNG CTPTC EMKPI

Bravo you have encrypted your first code...

Polysubstituted ciphers: in this we follow different pattern for text for each position at the code block,for example let us encode the same text used above using polysubstituted block cipher
Our text is "WELCOME TO FREE LEARN HACKING"
we will follow the steps:

1. first make block of fixed length for text say 5
   then our text will become WELCO METOF REELE AENHA CKING
2. now comes the crucial step deciding the key,let us decide the key as replace first alphabet by its first successor,second alphabet by its second successor,third alphabet by its third successor,fourth alphabet by its fourth successor,fifth alphabet by its fifth successor
   now our text will look like XGOGT NGWSK SGHPJ BTQLE DMLRL

Polysubstituted cipher is much hard to crack in compariso to monosubstituted cipher...
we will learn some more powerful ciphers in next article till then keep on making ur information secretive using these ciphers