Quantum Technologies How Will Cryptography Change?

Cryptography, or encryption, is used by websites and messaging apps to keep information secret. When you visit a website with a secure connection (i.e., one that displays a padlock icon next to the URL in your web browser) to make a purchase or log into your bank account, the website uses encryption to transfer data in a manner that prevents unauthorised access to your private information. Quantum information science, which exploits the properties of Quantum Technologies to develop new technologies, has the potential to alter our understanding of encryption in two significant ways.

Post-quantum cryptography, also known as quantum-proof cryptography, seeks to develop encryption methods that cannot be cracked by algorithms or calculations executed by future quantum computers. If and when quantum computers become a reality, current encryption methods will not necessarily remain secure.

Consider RSA cryptography

RSA is a widely-used secure data-transmission system upon which Internet browsers and digital signature software are constructed. It generates public and private sets of codes, or keys. When you use an internet browser or sign a document using a digital signature, for example, the process occurs in the background. The private key in RSA consists of two large prime numbers generated by an algorithm and kept confidential. Using an algorithm, the product of these two integers is combined with an exponent to generate the public key. Anyone can encrypt information using the public key, but only the owner of the private key can decrypt the information.

The encryption system relies on the fact that factoring the large integer in the public key to determine the two prime numbers that make up the private key is prohibitively time-consuming and computationally intensive. In contrast, Shor’s algorithm, which was published in 1994 by mathematician and Caltech alumnus Peter Shor (BS ’81), describes how, in theory, quantum computers could efficiently factor extremely large numbers. Therefore, Shor’s algorithm may be the undoing of RSA cryptography.

Quantum cryptography employs the laws of quantum physics to transmit confidential data in a manner that renders eavesdropping impossible. Quantum key distribution (QKD), the most extensively researched and practical method of quantum cryptography, employs a series of photons to transmit a secret, random sequence known as the key. Users will determine if the key has been compromised by comparing measurements obtained at both ends of the transmission. Someone who wiretapped a phone could intercept a secret code without the knowledge of the respondents. In contrast, there is no way to “listen in” on or observe a quantum encrypted key without disturbing the photons and altering the outcomes of the measurements at each end. This is because of a law in quantum mechanics known as the uncertainty principle, which states that measuring a property of a quantum system may alter other properties of the quantum object (in this instance, a photon).

“Perpetual Security”

Thomas Vidick, a Caltech professor of computation and mathematical sciences who teaches courses on quantum cryptography, asserts that QKD is only appropriate for data that must be kept private in the distant future.

“If you encrypt your data today using standard ways, it will probably stay secret for the next ten years. Today’s cryptography is predicated on maths that is difficult to solve, but in 50 years it may not be so difficult. Suitable for credit card transactions. It may not apply to medical records or government information that is intended to remain secret for a prolonged period of time.”

Is quantum cryptography currently in use?

The effectiveness of QKD has been demonstrated by scientists, but it is not extensively utilised due to significant technological limitations. A single-photon laser transmits a signal through a fibre optic cable, one photon at a time, in order to transmit a quantum key. This technique is slower than current communication technologies and requires the installation of a dedicated fibre optic cable between the two parties. For instance, Amazon could not use quantum encryption to secure customer transactions because it would require cables between its servers and the individual devices used to make purchases. Distance also plays a role. When fibre optic cables are used to transmit data, as in residential internet and cable systems, the data is sent over greater distances using repeaters. However, these repeaters disrupt the quantum state that is essential for QKD.

Using a combination of fibre optic cables with “trusted relay nodes” as repeaters and a satellite that transmits photons through the atmosphere, Chinese researchers have demonstrated QKD over long distances. However, additional research is required to develop a system that transmits keys efficiently and reliably.

Theoretically, quantum cryptography is unbreakable because eavesdropping is always detected, but its applications in practise are limited. Vidick states, “If you build a house, it will only be as strong as its weakest pillar.” “To create a truly usable system, it may be necessary to combine quantum cryptography with non-quantum elements, and these non-quantum elements may be susceptible to attacks that theorists have not considered.”


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