ABSTRACT: Quantum cryptography uses Quantum Key Distribution

ABSTRACT: In the existing world, the INTERNET is considered as one of the keys to communication. With the use of increase in the internet, transmission is made easier which made us use the internet as a foundation for communication.

When we are communicating through the internet, protecting our information is very important. Although we can protect our information from an unauthorized user in many ways, Researchers have come up with a new technology called QUANTUM CRYPTOGRAPHY which is used to send secure data by applying laws of Quantum Physics. It has achieved the cons of traditional cryptography. Quantum cryptography is going to be future of privacy. In this survey paper, we are going to discuss BB84 protocol used in Quantum cryptography. INTRODUCTION: To prevent unauthorized users from gaining the access to our private information, we use cryptography to turn our original data into an unreadable format. To provide privacy, we use a key for encoding and decoding of our information by using a key called Secret Key.

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Quantum cryptography uses Quantum Key Distribution which uses light to send information using a wonderful law of Quantum Mechanics 4. It is considered as one of the most remarkable technology in cryptography. In future, the modern computers may soon be replaced by Quantum Computers which is considered to be most secure in present technology.Classical cryptography: This type of cryptography is used to send messages secretly. In this, for the purpose of encoding and decoding of messages bits are used. The major problem in classical cryptography is considered to be Key Distribution.

There are two types of cryptosystems: Symmetric Key Cryptography knew as Traditional Cryptography and Asymmetric Key Cryptosystem. (1) Symmetric Cryptography: In this, we use the same key for both encryption and decryption Fig 1.0 Symmetric key Encryption 4(2) Asymmetric Cryptography: In this, we use two different keys, one for encryption one for decryption Fig 2.

0 Asymmetric Key Encryption 4QUANTUM CRYPTOGRAPHY: No secret would be safe, but the researchers have come up with a new cryptography called as QUANTUM CRYPTOGRAPHY-which is not only hard to break but may be impossible to break. This works by hiding the data in photons of light particles. The key of this cryptography is a stream of photons of light particles. In this, we use Qubits which are used to carry a unit of quantum data. We use Qubits as they possess special properties which help us to solve complex problems. The main motto of using this Quantum Cryptography is we can detect the presence of third-party when two users are communicating with each other, which is considered as the major advantage. This cryptography uses Quantum mechanics, Heisenberg Uncertainty Principle, and photon polarization. Heisenberg Uncertainty Principle: This principle states that it is not possible to locate the position of an atom when it is traveling through space.

This statement was given by a German physicist Werner Heisenberg in 1927. As per Heisenberg Uncertainty Principle, and we cannot measure the state of the photon, without disturbing the system. Polarization of Photon: The principle of this is, it won’t allow the eavesdropper to copy the data of Qubits as we are using non-cloning theorem. Photon Polarization can be described as converting the unpolarized light into polarized light in a specified direction of our own. These photons have a special property called spin which will change when they are passed through the filter. In this, we have four types’ of filters: two horizontal and two diagonal. Fig 3.0 Polarization by a FilterWORKING OF QUANTUM CRYPTOGRAPHY: The main theme of this technology is it can detect/block any kind of eavesdropping by applying the wonderful law of quantum physics.

Until and unless the eavesdropper knows which filter to use, he may take a risk of applying a wrong filter and has a chance of getting the wrong output and because of this, passing through the wrong filter, the intruder cannot get the correct output. When someone intercepts in the middle, the spin of the photon changes and the receiver may get a wrong output even after applying the correct filter. Quantum Mechanics is used as a technique to detect the eavesdropping Detecting Eavesdropping: It is not possible for someone who wants to intercept in the middle to monitor the transmission of photons without getting the photons altered. When the eavesdropper comes in the middle, he/she will apply some filter in order to get the information. In this process, he may apply the wrong filter and when the photon passes through that filter, the spin of that photon changes. After getting the information, he transfers the information to the receiver, as the spin changes, the receiver may probably get the wrong output. Because of getting the wrong output even after applying the right filter, the users will get to know that there has been someone who is trying to copy their information.

QUANTUM KEY DISTRIBUTION PROTOCOLS: These protocols provide secure transactions between two end users. It produces a shared random secret key which is known only to the users used to encrypt and decrypt the messages. It can only produce and distribute a key, but not to transmit any data. The key can be used with any encryption algorithm of our choice to encrypt/decrypt a message. BB84 PROTOCOL: It is considered the first quantum cryptography protocol. Bennett and Brassard with Stephen Wiesner proposed QPKD protocol in 1984, and later it is named as BB84 protocol 2. The goal of this protocol is to let two users communicate/exchange data between them securely. Let us consider two users Alice and Bob want to communicate with each other.

Suppose Alice wants to send information to Bob, they combined select a basis of which filter to use (rectilinear or diagonal). Alice sends the photons through selected filters as the polarized light of photons. Bob then uses the same basis selected by Alice and gets the photons send by Alice in a correct order. Fig 4.0 – Steps of BB84 ProtocolBB84 WITH NO EAVESDROPPING: To detect an Eavesdropping effect, Alice will send some random bits to check whether the channel is secure.

She includes some test bits in the subset. Alice will let the Bob know which basis she used to encode them. Bob will then use the same basis to decode the information. After decoding the information, Bob tells Alice what output he got. Fig 5.

0- Comparing Measurements The test bits allow Alice and Bob to detect whether the channel is secure. If some test bits are modified in the middle, they can guess that there is an Eavesdropper in middle of transmission.GETTING THE FINAL KEY: When both Sender and Receiver make sure that the channel is secure, the test bits they used in the transaction are discarded and they will then select the Final Key from the other bits which are known only to them Fig 6.

0 – Getting the Final KeyCONCLUSION: Quantum cryptography is different from any other encryption systems before. It is considered as one of the major security development in the software industry. As this technology gets implemented, we can have secure communications and transactions in bank sectors etc. People think that it is a whole new era of privacy.

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