### Abstract— citizens are using networks for different works

Abstract—

for the first few decades of their existence, computer networks were mainly

used by universities researches for sending mails and by corporate employees

for sharing printers. So for then, security did not get a lot of attention. But

now millions of ordinary citizens are using networks for different works like,

banking, shopping etc. so the requirement of computer security increases. The

requirement of information security within an organization have undergone two

major changes in the last several decades. With the introduction of computer

the need for automated tools for protecting files and other information stored

on the computer became an evident. This is especially the case for a shared

system, such as time sharing system and the need is even more acute for systems

that can be accessed for a public telephone or a data network. The generic name

for the collection of tools to protect data is “Computer Security or

Cryptography”.

Introduction

Cryptography is the practice and study of techniques

for secure communication in the presence of third parties (Adversaries).

Or

Cryptography is the science of using mathematics to

encrypt and decrypt data. The word Cryptography is defined from the Greek work

krypto which means “Secret Writing”. More generally, it is about constructing

and analysing that overcome the influence of adversaries and which are related

to various aspects in information security such as data confidentiality, data

integrity and authentication. Cryptography is a vital of today’s computer and

communications networks, protecting everything from business e-mail to bank

transaction and internet shopping while classical and modern cryptography

employ various mathematical techniques to avoid eavesdroppers from learning the

contents of encrypted messages. Computer system and networks which are storing,

processing and communicating sensitive or valuable information require

protection against such unauthorized access.

I.

Terminology

1. Cryptography— Study

of encryption principles and methods.

2. Plain Text — Original Messages.

3. Cipher Text —coded messages.

4. Encrypt

— Convert plain text into coded text.

5. Decrypt— Convert Cipher text into Plain Text.

Fig: 01

II.

Encryption

The process of Converting Plain Text into an

unintelligent format (Cipher Text) is Called Encryption.

III.

Decryption

The process of converting Cipher Text into

a plain Text is called decryption.

IV.

Purpose of Cryptography

1. Authentication: The process of proving one’s identity.

2. Privacy/Confidentiality: Ensuring

that no one can read the message except the intended receiver.

3. Integrity: Assuring the receiver that the

receive message has not been altered in any way from the original.

4. Non-Repudiation: A mechanism to prove that the

sender really sent this message

How does

Cryptography work???

The message to be encrypted is known as PLAIN TEXT, are transformed by a

function that is parameterized by a key. The output of the encryption process,

known as the CIPHER TEXT, is then

transmitted, often by messenger or radio. We assume that the enemy, or

intruder, hears and accurately copies down the complete Cipher Text. However,

unlike the intended recipient, he does now know what the decryption key is and

cannot decrypt the cipher text easily. Sometime the adversaries cannot only

listen the message, but also record that message and play them back later, by

inject his own messages. The art of breaking Cipher, called Cryptanalysis, and the art devising

them (Cryptography) is collectively known as Cryptology.

It will often be useful

to have a notation for relating plain text, Cipher text and keys. We will use C=EK (P) to mean that he encryption of

the plaintext C. Similarly, P=DK(C) represents

the decryption of C to get the

plaintext again.

V.

Strong

cryptography

“There are two kinds of

cryptography in this world: Cryptography that will stop your kid Sisters from

reading your files, and Cryptography that will stop major governments from

reading your files”,

VI.

Cryptography

Techniques

There are two basic

techniques for encrypting information:

Symmetric

Encryption (also called Secret key Encryption).

Asymmetric

Encryption (also called Public Key Encryption).

VII.

Key

It is a secret piece of

information that customize how the Cipher Text is transmitted into Plain Text.

Secret Key Cryptography

Also known as Symmetric

Key Cryptography. Sender and receiver use the same key and an

encryption/decryption algorithm to encrypt/decrypt data i.e. the key is shared.

Symmetric Key is Simpler and Faster but less secure.

Fig: 02

Public Key Cryptography

The problem of key distribution are

solved by Public Key Cryptography. Public key Cryptography is an asymmetric

scheme that uses a pair of keys for encryption: a public Key, which encrypts

data, and a corresponding private key to the world while keeping your private

key Secret. It is computationally infeasible to deduce the private key from the

public Key. Anyone who has the public key can encrypt information but cannot

decrypt it. Only the person who has corresponding private key can decrypt the

information. It is more secured and relatively complex.

Fig: 03

VIII.

Conclusion

Network security is the

most vital component in information security because it is responsible for

securing all information passed through networked computers. We have studied

various cryptographic techniques to increase the security of networked.

Cryptography, together with suitable communication protocols, can provide a

high degree of protection in digital communication against intruder attacks as

far as the communication between two different computers is concerned. By using of

encryption techniques a fair unit of confidentiality,

authentication, integrity, access control and availability of data is

maintained.