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A Brief Introduction to Cryptography


Nowadays the Internet is an important part of Life.  We are using the Internet for sending confidential data also like password, for storing army secrets. But the Internet is insecure medium.  Do you know why?
 
Insecure Medium:
Imagine you are sending a data.  In the internet world, data are separated as packets and send to the destination.  Do you think the data directly reaching the destination?   If you think so, ) .you are wrong.  The packets are going through different routers.  Finally, the data is sent to the user.  In this gap, Intruders(i mean attackers) takes advantages.  Intruders can see what you are sending.  Because your data are simple and easy to readable by anyone.


How to secure the data?
We can not stop the intruders and their activities.  But we can make our data as Unreadable for Intruders.  For this purpose, the Cryptography is introduced.

Introduction to Cryptography:
Julius Ceaser who introduce the Cryptography technology.  Cryptography is technology in which we are changing the plain text to unreadable text(known as cypher t).

In your home you put money in the locker,  Isn’t it?  The locker probably has the key to open.  Imagine thief is coming to your home to steal.  if he wants to open the locker, certainly he needs the key.  Without the key, he can not do. Yeah, I can hear what you are saying, he can break the locker.  If the locker is very strong, he can not open it at all.

Likewise in cryptography also we are going to create a Key for our data.  So that Intruders can not read the data.  It is possible to read the data if the encryption(will explain later) is weak.  So we need to encryption method very strong.

Terminologies used In cryptography: Plain Text:
original data or text is known as Plain text.
Cipher Text:
The encrypted message(unreadable message).
Encryption:
Changing the Plain text to unreadable.
Decryption:
Changing the cypher text to plain text.


Traditional Encryption Methods:

  • Ceaser Cipher
  • Mono Alphabetic Cipher
  • Play Fair Cipher
  • Hill cipher
  • PolyAlphabetic Cipher
  • Rail Fence Technique.
Ceaser Cipher:
  Simplest encryption method.  In this method, we are going to replace the alphabets with shifted alphabets.


Eg:
Consider Plain text is:  break
if we use Key is 3, then the cipher text will be  found by:


 b+3 r+3 e+3 a+3 k+3
Shifted to three alphabets final ciphertext is:

euhdn


If the intruders see the cypher text(here “Kuhn”) , hackable .he can not understand anything.   But this method hackable.  Because intruders can try 25 shifts and finally he can get the result.
Many encryption methods are introduced to make better security.

Today  Encryption methods:

  •  AES(Advanced Encryption Standard)
  • DES(Data Encryption Standard)
  • RSA(Name of the creators).
  • MD5(Message Digest -5)
  • SHA(Secure Hash Algorithm
For the secure transaction, SSL (Secure Socket Layer ) is introduced.

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