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Security in Quantum Era enabled through Quantum Cryptography
Somya Agarwal Senior Management Trainee | November 19, 2020

Across all the sectors, there are a few common trends such as increased digitization, proliferation of IoT, and increased device connectivity. Such trends bring increased risks, threats, and vulnerabilities to data, devices, and systems. Scientists, engineers, and researchers rely on various cryptography methods to securely process and transmit information across distances. The most popular types are public and private key cryptography. There are broadly two aspects to cryptography. One is the algorithm and the other is a key. For implementing secure cryptography, relying on the security of the key is more important than relying on the security of the algorithm, as algorithm information is publicly available. The security of the key is of utmost importance. Without the key, it is impossible to decrypt the information.

Due to increased threat perception, and with computers becoming more powerful, the already existing algorithms can be decoded and the keys can be stolen. Security experts are looking beyond classical cryptography, which is based primarily on mathematics. They are now looking toward quantum cryptography – based on physics and quantum mechanical phenomena of subatomic particles like photons – to offer secure solutions to key exchange problems.

Quantum cryptography is based on the usage of particles/ waves of light and their intrinsic quantum properties to develop keys that are used with an algorithm to send information.

Quantum cryptography is based on the usage of individual particles/waves of light (photon) and their intrinsic quantum properties, to develop keys that are used with an algorithm to send the information. In Quantum Cryptography, a classical algorithm such as RSA, DES, etc. can be used to encrypt the information, and quantum coding is used to generate & send the key. This is known as Quantum Key Distribution. It works on the protocol BB84, which was developed in 1984 by Bennet and Brassard. Quantum cryptography system will allow for a more secure transfer of the keys with this technique of Quantum Key Distribution (QKD).

Quantum cryptography can solve key exchange problems which classical cryptography cannot through Quantum Key Distribution (QKD technology)

In Quantum Key Distribution (QKD), photons are used to generate the key for cryptography and a classical encryption/decryption algorithm may be used. As per the intrinsic property of photons, it is not possible to measure the photons without altering its behavior. Due to this intrinsic property of photons, any system secured by quantum cryptography is more secure against attacks such as eavesdropping or passive interception.

Photons particles are small discrete packets of light, with no mass and it can spin in all the possible directions at once. This state of light/photon is known as the unpolarized state. For the creation of unpolarized photons LEDs (Light Emitting Diodes) can be used. LEDs can create a single photon at a time rather than multiple photons at the same time. To convert an unpolarized photon into polarized photon, polarization filters can be used. A photon, with the help of different polarization filters, can take 4 possible spin states. The inherent property of photon particles is that once they are polarized, it becomes impossible to measure photons with a filter, except by a filter like the one that initially produced their current spin. For example, if a photon with a circular spin ( / ) is measured through a vertical filter ( | ), either the photon will not pass through the filter or the filter will change the photon's polarization, causing it to take a vertical spin ( | ). Due to this, the information on the photon's original polarization is lost, and also any information attached to the photon's spin is lost.

The potential applications of QKD network include securing critical infrastructures (for instance, the Smart Grid), financial institutions such as banks, and national security. China is in the process of deployment of a 2000 km QKD network between Shanghai and Beijing. In Tokyo, QKD technology was used to transfer sensitive genome data between two sites. UK and Singapore have collaborated to co-develop a ‘QKD Qubesat’ satellite, which is expected to be operational by 2021. It is based on the CubeSat standard that will use QKD technology from Singapore to test the secure distribution of cryptographic keys over distances.

Standardization bodies are already working on standards to make this process easier. The National Institute of Standards and Technology (NIST) has selected 15 algorithm submissions for the third phase of a research competition focused on quantum computing-based cryptography. By 2022, NIST plans to choose algorithms and standardize them.

Challenges in Quantum Key Distribution (QKD)

  • The original quantum cryptography system was built in 1989 by Charles Bennett, Gilles Brassard, and John Smolin which sent cryptographic keys over a distance of 36 centimeters. Since then, with more technological advancements newer models have reached a maximum distance of 150 kilometers (about 93 miles). This new distance is still far short of the current distance requirements needed to transmit information with a modern computer and telecommunication system.
  • The cost of equipment and infrastructure required to implement quantum cryptography is quite high.
  • Because of the distance that a subatomic particle needs to travel, due to interference with other particles, the qubits may interchange from 1 to 0 and vice-versa.