Editorial Feature

Quantum Cryptography

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Quantum technologies are gaining a lot of interest at the moment, and these technologies range from quantum computing, quantum optics, and quantum communication technologies. One of the key features of quantum technologies is that they are meant to be much safer than classical technologies.

The reason that quantum technologies are set to be more safe than classical technologies is that they have an extra layer of encryption (alongside the classical channels) that enables data to be transferred with a much lower possibility of it being hacked and stolen. This is quantum cryptography.

Quantum Cryptography

While quantum cryptography is the general field of encrypting quantum technologies and making them safer for use, it is an area where there are different technologies and mechanisms that can provide an extra safety layer. The defining feature of these technologies, and one of the reasons why quantum technologies have such promise in a world where hacking is commonplace, is that certain cryptographic tasks can only be performed through the quantum network, and as such are not possible with classical networks. This makes them much harder to hack, as it is impossible to copy data that exists in a quantum state, as the superimposable nature of the quantum states (and ability to exist in more than one state simultaneously), means that the quantum state will be switched and the data can’t be retrieved. So, in theory, quantum technologies are not hackable, but we will see if this manifests in practice when quantum technologies are used in the real world.

Quantum Key Distribution

The most prominent quantum cryptography technology is quantum key distribution, and a lot of work has been done over the last few years on this encryption technology. It is an encryption method that has already found use in high value transactions. Quantum key distribution is a technology that doesn’t encrypt the data itself, but it is a method that encrypts the communication channels between users. In quantum key distribution, secure ‘keys’ are distributed between users. These keys are a random number sequence that is generated from the random polarization of photons.

These types of quantum cryptographic systems utilize more than one communication channel—the safer quantum communication channel, as well as the conventional classical channel. Both channels have a role to play in the encryption between communication points. The classical communication channel operates as normal, but this channel can also be used as a way of seeing if anyone has tried to hack into the system. This is because no data is contained in this channel, but it can still be penetrated by hackers. The data in quantum key distribution communication lines is transmitted via the quantum network and is held within the quantum bits (qubits). So, even when hackers try to hack into the network, they will enter the data-empty classical network, but because classical networks have a highly correlated signal, any imperfections in the signal at the receiving end of the communication channel will show that a hacking attempt has taken place.

Quantum Cryptography Technologies

Two other quantum cryptography technologies which have the potential for use in quantum technologies are quantum coin flipping and quantum commitment. Both technologies are a type of protocol for when distrusted parties are involved. These technologies are based on only sending a qubit value or sequence to another party to ensure that the people are who they say they are.

Quantum coin flipping involves sending a random sequence of qubits via a single photon to someone who the first person does not trust. Once the receiving person receives the qubits, it changes (and will not give the same output again), meaning that if anyone tries to intercept the information, the interception is easily detectable. It is a process that is used when instructions are being issued over long distances, between parties that do not know each other. The receiving party has to take note of the sequences and the relaying of this information back to the sender can inform the sender whether the receiver is being truthful or not.

Quantum commitment is slightly different to quantum coin flipping, but it is also used with potentially distrustful parties. In this approach, a certain value is attached to the qubit(s) being sent over to a receiving party. However, the receiver cannot see this value until it is revealed by the sender. It is only revealed once the sender believes that the receiver is trustworthy, which is often determined via quantum coin-flipping. So, both encryption methods can be used together.


There are also various other quantum cryptography methods that are either in the idea or the testing stage, but as it stands, these encryption technologies are not quite as developed as the ones mentioned above. However, they could become more established in years to come and be used in conjunction with the more developed methods mentioned here. For quantum technologies to be realized worldwide, there will need to be a lot of quantum cryptographic methods utilized to keep all the data that will be generated, transferred, and stored safe.

Sources and Further Reading

  • “Quantum cryptography”- Gisin N. et al, Reviews of Modern Physics¸ 2002, DOI: 10.1103/RevModPhys.74.145
  • “Quantum key distribution network for multiple applications”- Tajima A. et al, Quantum Science and Technology, 2017, 10.1088/2058-9565/aa7154
  • Quantum Cryptography - Extreme Tech

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Liam Critchley

Written by

Liam Critchley

Liam Critchley is a writer and journalist who specializes in Chemistry and Nanotechnology, with a MChem in Chemistry and Nanotechnology and M.Sc. Research in Chemical Engineering.


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