In day to day life the security of the data transferred through networks has become more important. The important message sending by army and many secrete agencies is done by various methods of encrypting algorithm and decrypting algorithm. This algorithm may be steganography, cryptography and many more. The paper contains the few details about Cryptography its algorithm and its types. This article tells us how cryptography is used to encrypt data and then decrypt data using various methods. Cryptography is basically the algorithm of sending the secrete message so that no unauthorized person cannot read the data. There are two types of cryptography method Classical cryptography and Quantum cryptography. Let us first learn few things about classical cryptography.

            Classical cryptography is also known as on-time pad method. It contains possible number plain text, possible number of cipher texts. Also key is used for encryption and decryption. The classical cryptography uses the mathematical way to send the secrete message. This becomes quite difficult to work with. Whereas quantum cryptograph yields solution to this in more efficient way.

            Bit is the most important representation in the computer. Here quantum system uses qubit representation of bits. Quantum cryptography is based on quantum mechanics. Quantum cryptography proves its efficiency in transfer of data by providing the facility to detect the presence of third party in the network who want to disturb the message or data.  Quantum cryptography uses qubits since qubits dose not allow cloning of the bits during transfer and so that the data cannot be disturbed and the originality of the data is maintained. Lets us have a look at the protocols used in quantum cryptography.

a.)    BB84 Protocol.

b.)    Ekert Protocol.

c.)    Quantum bit Protocol.

d.)   BB84 Quantum Bit Protocol.

Quantum cryptography data transfer takes place through the optic fiber and this may sometimes lead to problems in traversing the data at longer distance. Thus quantum key works more efficiently between the computers which are directly connected to each other and not in the machines connected to each other through optic fibers. The other drawback of the quantum cryptography is the users using this algorithm are not able to authenticate each other.

Concluding this paper tells us that Quantum cryptography is provides the feasible and the appropriate way to transfer the data by maintaining its secrecy. Further developments will help us to transfer this data through long distance. 

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