cryptography basics part iv

COMPOSITION OF CIPHERS

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In previous articles of cryptography we learnt how to encrypt a text using block substituted ciphers and transposition ciphers.these are good ciphers to a noob but these ciphers are cakewalk for a man having appreciable knowledge of cryptography.so let us make our ciphers even harder to crack using composition of ciphers.
so what really is composition of ciphers?? it is nothing but making a harder cipher using ciphers we already know.Double columnar cipher which we learnt in previous section is an example of this approach.
First let us apply this for block substituted ciphers.we learnt monosubstituted cipher and polysubstituted cipher.let us try to combine both the ciphers.
let us take the example "WELCOME TO FREE LEARN HACKING"

1. write the text in the blocks of length 5 "WELCO METOF REELE ARNHA CKING "
2. first applying key for polysubstituted cipher take 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
   our encrypted text will become "XGOGT NGWSK SGHPJ BTQLE DMLRL"
3. Now apply monosubstituted cipher ,deciding our key as replace each alphabet with their second successor like A from C
   now our text will become "YHPHU OHYTL JHIQK CURMF ENMSM"

This our new secret code and believe on me it is better than previous one.

Now let us experiment for route ciphers and columnar transposition cipher.we will be first performing route cipher and then columnar transposition

1. let us take the example "WELCOME TO FREE LEARN HACKING"
2. write the text in the blocks of length 5 "WELCO METOF REELE ARNHA CKING "
3. now we will apply route cipher therefore write in form according to the figure given below
   
4. now the encrypted text becomes WMRAC KINGA EFOCL EEERN HLOTE
5. now applying transposition cipher we get "WMRAC EEERN KINGA HLOTE EFOCL"
our new crypted text.

hey isnt it great forming powerful ciphers from existing ciphers we already know. we can also make composition of transposition cipher and substituted cipher, any permutation in your mind could result in a new cipher.

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

cryptography basic

CRYPTOGRAPHY BASICS

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What is cryptography?
cryptography is art of changing any simpler text to a secret code.so how are hacking and cryptography related?hacking is simply gaining access to any system,while the work of cryptography is to encode a simpler text to secret code to provide confidentiality and information security.having knowledge of cryptography helps to make our system more secure.

cryptography is study dealing with mathematics and computers both.so to achieve command on it we have to learn some basic mathematics.
lets catchup some information regarding functions..

what is functions?
let us take Y as a function of X
Domain:the values which is given as input
Range:the values which came as output
So elements in X constitutes domain,and elements in Y which are also called as image constitute range
it is a relation satisfying the below conditions
1.Each element of X should have one image in Y
2.No element in X could have two or more corresponding values in Y
3.Y could have one or more than one values of X
4.It is not mandatory that each element in Y should have corresponding X.

Bijective funtions:functions in which each element in X has only one image in Y and no element in Y should be empty

Inverse function:If Y is made to be codomain then X will automatically become image of Y if the function is bijective function, otherwise inverse of a function is not possible

Trapdoor one way functions:They are the most important type of functions for cryptography.By definition one way function is that function whose inverse is hard to find unless some very essential information is given which is called trapdoor.so for now only we will keep ourselves reserve with this definition only and will exploit trapdoor functions in our next topic