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You are here:Open notes-->CSSCryptography-->Cryptography

**Cryptography**

# How to study this subject

# Official Notes

# Notes from other sources

# Cryptography and its Types

Cryptography is technique of securing information and communications through use of codes so that only those person for whom the information is intended can understand it and process it. Thus preventing unauthorized access to information. The prefix “crypt” means “hidden” and suffix graphy means “writing”.

In Cryptography the techniques which are use to protect information are obtained from mathematical concepts and a set of rule based calculations known as algorithms to convert messages in ways that make it hard to decode it. These algorithms are used for cryptographic key generation, digital signing, verification to protect data privacy, web browsing on internet and to protect confidential transactions such as credit card and debit card transactions.

**Techniques used For Cryptography:**

In
today’s age of computers cryptography is often associated with the
process where an ordinary plain text is converted to cipher text which
is the text made such that intended receiver of the text can only decode
it and hence this process is known as encryption. The process of
conversion of cipher text to plain text this is known as decryption.

**Features Of Cryptography are as follows:**

**Confidentiality:**

Information can only be accessed by the person for whom it is intended and no other person except him can access it.**Integrity:**

Information cannot be modified in storage or transition between sender and intended receiver without any addition to information being detected.**Non-repudiation:**

The creator/sender of information cannot deny his or her intention to send information at later stage.**Authentication:**

The identities of sender and receiver are confirmed. As well as destination/origin of information is confirmed.

**Types Of Cryptography:**

In general there are three types Of cryptography:

**Symmetric Key Cryptography:**It
is an encryption system where the sender and receiver of message use a
single common key to encrypt and decrypt messages. Symmetric Key Systems
are faster and simpler but the problem is that sender and receiver have
to somehow exchange key in a secure manner. The most popular symmetric
key cryptography system is Data Encryption System(DES).

**Hash Functions:**There
is no usage of any key in this algorithm. A hash value with fixed
length is calculated as per the plain text which makes it impossible for
contents of plain text to be recovered. Many operating systems use hash
functions to encrypt passwords.

**Asymmetric Key Cryptography:**Under
this system a pair of keys is used to encrypt and decrypt information. A
public key is used for encryption and a private key is used for
decryption. Public key and Private Key are different. Even if the public
key is known by everyone the intended receiver can only decode it
because he alone knows the private key.

Playfair Cipher with Examples

Hill Cipher

Vigenère Cipher

Caesar Cipher in Cryptography

Substitution Cipher

Keyword Cipher

**Difference between Monoalphabetic Cipher and Polyalphabetic Cipher**

Difference between Block Cipher and Stream Cipher

Block Cipher modes of Operation

Data encryption standard (DES) | Set 1

Difference between AES and DES ciphers

RSA Algorithm in Cryptography

Implementation of Diffie-Hellman Algorithm