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Introduction :

There is an obvious need to communicate or to keep certain information unknown to the public or to anyone except those, who are intended to know that information. Cryptography is the process of achieving this result. Basically, Cryptography is the art and science of keeping messages secure. When we say

messages we could be referring to plain text files as well as any other types of files such

as executable files. Basically, the point of cryptography is to allow any user to keep his

data secure and not readable from not desired individuals. In this paper we discuss about Cryptography, types of Cryptography, importance of Cryptography and an application of it.

What is Cryptography?

Cryptography is the art of changing the form of the original information (the plain text) so that it becomes unintelligible for anybody except for those, who are intended to understand it. This process is called encoding. The result of the encoding is the cipher text. The process of restoring the original form of the information is the decoding or deciphering.

Key :

So-called secure methods of encoding and decoding digital information use some information in addition to the original data; this is the cryptographic key, or simply the key. The knowledge of the key is crucial for the decoding process. Everyone who knows this key (and the applicable method) is able to restore the original data.

Cryptosystem :

A cryptosystem (or cryptographic system) is the package of all procedures, protocols, cryptographic algorithms and instructions used for encoding and decoding messages using cryptography.

There are two kinds of cryptosystems: symmetric and asymmetric.

a) Symmetric cryptosystem: A cryptosystem that uses the same key(secret key) for encryption as decryption. This is also called Private Key Cryptosystem. Only people who are authorized to encrypt/decrypt the messages should know the key.

b) Asymmetric cryptosystem: A cryptosystem that had different keys for encryption(public key) and decryption(private key) and is impossible to derive the decryption key from the encryption key. This is also called the Public Key Cryptosystem. For this system encryption key is made public and the decryption key is kept secret.

Private or Symmetric or Secret Key Cryptography

Secret-key encryption uses one key, the secret key, to both encrypt and decrypt messages. This is also called symmetric encryption. The term "private key" is often used inappropriately to refer to the secret key.

In secret-key cryptography schemes, a single key is used to encrypt data. A secret key may be held by one person or exchanged between the sender and the receiver of a message. For example, if you encrypt data for storage on a hard drive, you remember the key and usually don't give it to someone else. But if you want to send secure messages to a business partner using symmetric cryptography, you need to make sure your partner knows the key that will decrypt the messages.

If secret-key cryptography is used to send secret messages between two parties, both the sender and receiver must have a copy of the secret key. However, the key may be compromised during transit. If you know the party you are exchanging messages with, you can give them the key in advance. However, if you need to send an encrypted message to someone you have never met, you'll need to figure out a way to exchange keys in a secure way. One method is to send it via another secure channel or even via overnight express, but this may be risky in some cases.

As mentioned, secret-key cryptography is often used to encrypt data on hard drives. The person encrypting the data holds the key privately and there is no problem with key distribution. Secret-key cryptography is also used for communication devices like bridges that encrypt all data that cross the link. A network administrator programs two devices with the same key, and then

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