# What is Quantum Cryptography?

**Cryptography**

The process of concealing or coding information so that only the intended recipient can read it is known as cryptography. **Cryptography** has been used to code messages for thousands of years and is still used in bank cards, computer passwords, and e-commerce.

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**Table of Content:**

**What is meant by Quantum Cryptography?****QKD’s History****What is the distinction between post-quantum and quantum cryptography?****How does Quantum Cryptography Work?****Difficulties in Quantum Cryptography****Conclusion**

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**What is meant by Quantum Cryptography?**

The process of encrypting data or converting plain text into scrambled text that can only be read by someone with the appropriate “key” is known as cryptography. By extension, quantum cryptography simply employs quantum mechanics principles to encrypt and transmit data in an unhackable manner.

While the definition appears straightforward, the complexity lies in the quantum mechanics principles that underpin quantum cryptography, which include:

- The particles that make up the universe are inherently uncertain and can exist in multiple locations or states at the same time.
- Photons are generated at random in one of two quantum states.
- A quantum property cannot be measured without causing it to change or be disturbed.
- Some quantum properties of a particle, but not the entire particle, can be cloned.
- All of these principles have an impact on how quantum cryptography works.

QKD enables two parties to generate and share a key that is then used to encrypt and decrypt messages. QKD refers to the method of distributing the key rather than the key itself or the messages it enables users to send.

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**QKD’s History**

In the 1970s, Columbia University’s Stephen Wiesner proposed quantum conjugate coding, which was the first proposal of quantum cryptography. Wiesner’s paper appeared in 1983. Years later, Charles H. Bennett developed the concept of secure communication based on Wiesner’s work. Bennett also invented BB84, the first quantum cryptography protocol to use nonorthogonal states. Furthermore, Artur Ekert discovered another method to QKD based on quantum entanglement in 1990.

**What is the distinction between post-quantum and quantum cryptography?**

- Post-quantum cryptography refers to cryptographic algorithms (typically public-key algorithms) that are thought to be secure against a quantum computer attack. These complex mathematical equations can be solved by traditional computers in months or even years. Quantum computers running Shor’s algorithm, on the other hand, will be able to break math-based systems in seconds.
- Unlike mathematical encryption, quantum cryptography uses quantum mechanics principles to send secure messages and is completely unhackable.

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**How does Quantum Cryptography Work?**

- QKD transmits light particles, or photons, between parties via fiber optic cables. Each photon has a different quantum state, and when they are sent together, they form a stream of ones and zeros.
- In this stream of quantum states that make up ones and zeros, qubits are the binary equivalent of bits. When a photon arrives at its destination, it is forced to take one of two paths into a photon collector by a beam splitter.
- The receiver will then send data about the sequence of photons sent to the original sender, which the sender will compare to the emitter, which would have sent each photon.
- Photons in the wrong beam collector are discarded, leaving only a specific bit sequence. This bit sequence can then be used as a key to encrypt data. Any errors and data leakage are removed during the error correction and other post-processing steps.
- Delayed privacy amplification is another post-processing step that removes any information an eavesdropper may have gleaned about the final secret key.
- The two most common types of QKD are prepare-and-measure protocols and Entanglement-based protocols. The focus of prepare-and-measure protocols is the measurement of unknown quantum states.

This protocol is capable of detecting eavesdropping and determining how much data was potentially intercepted.

- Entanglement-based protocols deal with quantum states in which two objects are linked to form a combined quantum state. Entanglement states that measuring one object has an effect on the other.

If an eavesdropper gains access to a previously trusted node and modifies something, the other parties will be notified.

- The mere act of attempting to observe photons changes the system, making an intrusion detectable by implementing quantum entanglement or quantum superpositions.
- Discrete variable QKD (DV-QKD) and continuous variable QKD are two other types of QKD (CV-QKD). DV-QKD will encode quantum information in variables and use a photon detector to measure quantum states.
- A DV-QKD protocol is an example of the BB84 protocol. Before sending light to a receiver, CV-QKD encodes quantum information on the amplitude and phase quadrants of a laser. The Silberhorn protocol employs this method.

**Here are some examples of QKD protocols:**

- Decoy state
- BB84
- E91
- Silberhorn
- KMB09

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**Difficulties in Quantum Cryptography**

**The three major challenges to QKD are:**

- the integration of QKD systems into the current infrastructure
- the distance photons can travel
- the use of QKD in the first place.

For the time being, establishing an ideal infrastructure for QKD is difficult. Although QKD is completely secure in theory, flaws in tools such as single photon detectors create numerous security vulnerabilities in practice. It is critical to think about security analysis.

One of the most significant challenges of QKD is that it relies on a pre-existing classically authenticated communication channel. This means that at least one of the participants has already exchanged a symmetric key, resulting in an adequate level of security. Another advanced **encryption**** **standard can be used to secure a system without using QKD. However, as the use of quantum computers increases, so does the possibility of an attacker exploiting quantum computing’s ability to crack existing encryption methods, making QKD more relevant.

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**Conclusion**

New technology is being developed all the time to improve high data rates and increase the overall effective distance of QKD. With new networks and companies offering commercial QKD systems, QKD is becoming more widely used in commercial settings.

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