cryptography basics part iii

CRYPTOGRAPHIC BASICS PART III

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In previous article we learnt about classification of cipher codes and then detailed analysis of two types of block ciphers maonosubstituted block cipher and polysubstituted block cipher.
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
cryptography basics part ii
today we will look to another type of block cipher known as transposition cipher,
Transposition cipher:It follows method of encryption by which position of simple text are shifted according to a regular pattern to form cipher text.
We will discuss three types of transposition ciphers here

• route cipher: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. now write in form according to the figure given below
     
  3. now the encrypted text becomes WMRAC KINGA EFOCL EEERN HLOTE
• columnar transposition:

we will use the same text "WELCOME TO FREE LEARN HACKING"

1. write the text in the blocks of length 5 "WELCO METOF REELE ARNHA CKING "
2. now write in form given below
   1 3 5 2 4
   W M R A C
   E E E R K
   L T E N I
   C O L H N
   O F E A G
3. now we have to chose a key suppose we chose our key as "CRYPT" then we will mark it in ascending order C-1 P-2 R-3 T-4 Y-5 whichever occurs first in alphabets
4. now the encrypted text becomes WMRAC COLHN EEERK OFEAG LTENI

double columnar transposition:

here we will repeat the same task two times we will use the same text "WELCOME TO FREE LEARN HACKING"

1. write the text in the blocks of length 5 "WELCO METOF REELE ARNHA CKING "
2. now write in form given below
   1 3 5 2 4
   W M R A C
   E E E R K
   L T E N I
   C O L H N
   O F E A G
3. now we have to chose a key suppose we chose our key as "CRYPT" then we will mark it in ascending order C-1 P-2 R-3 T-4 Y-5 whichever occurs first in alphabets
4. now the new text becomes
   1 3 5 2 4
   W M R A C
   C O L H N
   E E E R K
   O F E A G
   L T E N I
5. Now we will again apply the key crypt in the same manner
6. our encrypted text become WCEOL AHRAN MOEFT CNKGI RLEEE

There are hundreds of types of transposition cipher available.you can also make your own transposition cipher but it should be logically correct.
Transposition ciphers prove to be better cipher than substitution cipher
In next article we will be getting knowledge of more different powerful techniques.

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