Abstract— is even more acute for systems

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


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Cryptography is the practice and study of techniques
for secure communication in the presence of third parties (Adversaries).


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.




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


The process of Converting Plain Text into an
unintelligent format (Cipher Text) is Called Encryption.


The process of converting Cipher Text into
a plain Text is called decryption.


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.   



“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”,



There are two basic
techniques for encrypting information:

Encryption (also called Secret key Encryption).

Encryption (also called Public Key Encryption).



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


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