# Cryptography PPT Presentation

## Introduction to Cryptography PPT Presentation:

We all have head a lot about cryptography. Let us learn some things in detail about cryptography in this document. Cryptography was long back discovered and used by Egyptians 4000 years back. Let us learn types of cryptography.

a.)    Mono alphabetic Cipher

In this type the message or cipher text is being read or decoded based on the frequencies of the occurrence of the letters or words.

It is further classified in

a.)    Stream Cipher

Stream cipher as the name suggests each character is being replaced from the plain text. Stream cipher encrypts one character at a time and decrypts one character one at time. One bit at a time is considered for encryption and decryption in stream cipher.

b.)  Block Cipher

In block cipher block of characters is being considered at a time and encrypted.      Block cipher encrypts and decrypts a block of characters XOR combination of blocks in being considered.

b.)    Vigenere

This method of cryptography is based on shifting of alphabets in plain text.

One time pad contains less repetition of text equally longer to plain text. One time pad helps to maintain perfect secrecy as there are number of combinations can be formed.

d.)    Play Fair

Play fair was invented by Sir Charles Wheatstone. In this method of cryptography a matrix of 5X5 is being considered. If two same letters are found in a same Colum then it is being replaced by the next letter. Or the two letters ate kept at the two corner of the rectangle. Birthday theorem is also used.

e.)    Feistel cipher

Feistel cipher was being developed by IBM developers in the year 1950’s. Luby – Rackoff’s proof of feistel Cipher.

f.)     DES

Des is most popular cryptography algorithm. It was been developed by IBM in 1947. After two years NBS (now called as NIST) made advancements in this algorithm. But there was some drawback of DES to overcome them 3DES was been developed and it is more secure than DES.

g.)    AES

3DES was secure but it operability was slow and to overcome its drawbacks NIST invented AES (Advanced Encryption Standard). After this Rijindael algorithm was also invented and it was more efficient, well adaptable to modern processors, suitable for smart cards, flexible and dedicated in terms of hardware.
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