QNu Labs


Quantum 101: A Dive into Quantum Cryptography

FEBRUARY 20, 2024 | QNu Labs

In cybersecurity, where data protection is paramount, traditional cryptographic methods have long been the stalwart guardians of sensitive information. However, as computing power advances, so too do the tools available to potential attackers. In the ever-evolving landscape, the emergence of quantum cryptography offers a promising solution to the challenges of secure communication in the digital age.

Understanding Quantum Cryptography

Quantum cryptography could well be the first application of quantum mechanics at the single-quantum level.

Unlike traditional cryptography, which is built on mathematics, quantum cryptography is built on the laws of physics. Specifically, quantum cryptography relies on the unique principles of quantum mechanics:

  • Particles are inherently uncertain: On a quantum level, particles can simultaneously exist in more than one place or more than one state of being at the same time, and it is impossible to predict their exact quantum state.
  • Photons can be measured randomly in binary positions: Photons, the smallest particles of light, can be set to have specific polarities, or spins, which can serve as a binary counterpart for the ones and zeros of classical computational systems.
  • A quantum system cannot be measured without being altered: According to the laws of quantum physics, the basic act of measuring or even observing a quantum system will always have a measurable effect on that system.
  • Particles can be partially, but not cloned: While the properties of some particles can be cloned, a 100% clone is believed to be impossible.

Quantum Key Distribution (QKD)

Quantum Key Distribution is one of the foundational concepts of quantum cryptography. QKD enables two parties to generate a shared secret key with which they can encrypt and decrypt messages securely. The underlying idea is the use of quantum properties to detect any attempt to eavesdrop on the communication.

How It Works

QKD systems work by sending individual photon light particles across a fibre optic cable. This stream of photons travels in a single direction and each one represents a single bit, or qubit, of data—either zero or one. Polarised filters on the sender’s side change the physical orientation of each single photon to a specific position, and the receiver uses two available beam splitters to read the position of each photon as they’re received. The sender and receiver compare the sent photon positions to the decoded positions, and the set that matches becomes the key. 

To better understand QKD, imagine two people, Alice and Bob, who need to establish a secure connection. They can use QKD to create a secure cryptographic key by sending polarised photons over a fibre optic cable. The cable doesn’t need to be secured because each photon will have its own randomised quantum state. Should someone, let’s call her Eve, be eavesdropping, Alice and Bob will always be able to tell because it’s impossible to observe a quantum state without also affecting it. In this way, QKD systems are considered to be unhackable. If Bob and Alice detect a change in the quantum states of the photons, they’ll know Eve is eavesdropping. And if Eve is eavesdropping, Bob and Alice will always be able to detect it.

Why is quantum cryptography important?

To date, traditional data encryption has generally been sufficient for maintaining secure communications in most cybersecurity settings. However, the rise of quantum computing poses an existential threat to even the most secure traditional cryptographic algorithms.

Like quantum cryptography, quantum computing is a rapidly emerging technology that also harnesses the laws of quantum mechanics. Compared to our fastest and most cutting-edge classical computers, quantum computers have the potential to solve complex problems orders of magnitude faster. 

Today’s cryptosystems can be divided into two main categories, symmetric systems, which use one secret key to both encrypt and decrypt data, and asymmetric systems, which use a public key that anyone can read and private keys that only authorised parties can access. Both types of cryptosystems create these keys by multiplying large prime numbers and rely on the massive computing power required for factoring large numbers to ensure that these encryption keys can’t be cracked by eavesdroppers or hackers.

Even the most powerful supercomputers on earth would require thousands of years to mathematically break modern encryption algorithms like the Advanced Encryption Standard (AES) or RSA.

But a fully functional quantum computer—should one be perfected—could potentially find the solution in only a matter of minutes.

For this reason, the use cases for quantum cryptography are endless. If anything from corporate information to state secrets must be kept secure, when quantum computing renders existing cryptographic algorithms obsolete, quantum cryptography may be our only recourse for securing private data. 

The Road Ahead

Ongoing research and technological advancements continue to push the boundaries of quantum cryptography. Innovations in quantum hardware, such as the development of more efficient qubit storage and manipulation techniques, promise to make quantum cryptographic systems more accessible in the future.

As we look ahead, the integration of quantum cryptography into existing communication networks could herald a new era of secure and private communication, safeguarding sensitive information against the ever-present threat of cyberattacks.



American Physical Society