Quantum Cryptography For Beginners: From Basics To Blockchain by@karkuzhali

Quantum Cryptography For Beginners: From Basics To Blockchain

Karkuzhali Selvarajan HackerNoon profile picture

Karkuzhali Selvarajan

Postgraduate Theoretical Physicist. Science Enthusiast. Also interested in inducing existential blues, haha.

You might have already heard about the calamitous and incontrovertible threat that quantum computing poses to our traditional security system, leading to a global crash in the digital economy and the potential end of the world as we know it. But did you also know that quantum cryptography (QC) not only solves the quantum threat and potentially scales the blockchain to an entirely new level?

In 2016, NIST started an open competition for quantum-safe algorithms that will enable information security against quantum attacks. Since then, many tech companies have joined the race and started to commercialize post-quantum cryptography (PQC). On the other hand, studies suggest that PQC is not a viable solution and that cryptosystem based on quantum mechanics is the ultimatum. To help explain this concept, we’ll talk about 

What quantum mechanics takes away with one hand and gives back with the other. 

Furthermore, we’ll discuss the basics of quantum cryptography and how it can help with web 3.0.

Table of Contents

  1. Basics of Quantum Cryptography
  2. Quantum Cryptography + Blockchain = Quantum Blockchain?
  3. Quantum Key Distribution 
  4. The Quantum Internet 
  5. How Quantum Cryptography Can Help The Quantum Blockchain

Basics of Quantum Cryptography

1. What is Quantum Cryptography in Simple terms?

Quantum cryptography is a quantum information technology where cryptosystems are developed based on the principles of quantum mechanics rather than a complex math problem such as the ones used by RSA, Diffie-Hellman, & ECC. 

2. What is Quantum Cryptography used for? And what is quantum-safe cryptography?

Quantum cryptography is an alternative method to post-quantum cryptography to address the threats that a fully realized quantum computer poses by providing unconditional security or information-theoretic security. PQC is also known as quantum-safe or quantum resilient cryptography,

PQC uses classical algorithms that are believed to be robust to both quantum and classical threats to our security systems, but many researchers report that these efforts are a temporary solution. And it’s only a matter of time that development in quantum computing or the Number Theory supersedes it. This unviability of PQC propels the impending need for quantum cryptography.

3. Why Is Quantum Cryptography Unbreakable? 

The usage of quantum principles such as the uncertainty principle, entanglement, non-orthogonal quantum states, etc., to develop algorithms and schemes makes quantum cryptography unbreakable in theory. The only question of information security with QC then comes from the interoperability of quantum cryptography with our classical infrastructures such as consensus and other protocols.

Quantum Cryptography + Blockchain = Quantum Blockchain?

While blockchain is the current digital revolution, estimates predict that we’ll develop a functional quantum computer in the next few decades, at the earliest. 

To comply with these advancements on both the quantum and the blockchain front, researchers and industry experts have been working on the framework of the quantum blockchain based on quantum cryptography for a while now. 

Blockchain doesn’t need an introduction, but here’s a quick summary: Blockchain is a type of immutable and consensus-based distributed ledger technology (DLT). The key purpose of Blockchain and other such DLTs is to establish a decentralized and trustless peer-to-peer network, to eliminate the need for intermediaries in many business sectors.

But what is quantum blockchain? It is a type of DLT based on the quantum key distribution (QKD) and other quantum cryptographic schemes. 

Quantum Key Distribution 

Quantum key distribution is a quantum cryptography method that is used to securely generate and distribute secret keys using the laws of quantum mechanics. Blockchain is pretty secure on paper, but threats against it both from hackers and the quantum are still a major problem. Thus, QKD aims to establish a new cryptosystem with information-theoretic security, that is better than our conventional system. 

QKD protocols are broadly Discrete-variable (DV) and Continuous-variable (CV) based. DV-QKD encodes information on a single photon to transmit information, whereas CV-QKD encodes information on the amplitude and phase quadrature of a beam of photons. The differences between DV & CV-based QKD also come from its detection techniques and efficiency.   


A QKD communication channel.

To successfully establish QKD networks, the problems with quantum teleportation need to be addressed. This is because bits of quantum information can’t be transmitted in long distances, due to the no-cloning theorem. They can only be teleported from one location to another, and there is a problem with decoherence too. 

In the quantum blockchain, QKD is the key protocol that will authenticate all transactions. As of now, a functional quantum cryptography protocol that can achieve reasonably high key rates at long distances has two conundrums: 

A fully device-independent QKD is secure on all grounds but it has very low key rates. On the other hand, a more practical QKD requires some level of trust with the source and measurement device which makes it vulnerable to side-channel attacks.   

This is the trade-off between security, key rates, and distance with QKD protocols that exist today. 

The Quantum Internet

While controversy still brews around the quantum supremacy domain, the field of quantum information has progressed. Companies such as ID Quantique, Samsung, and many others have commercialized quantum cryptography and are preparing for the post-quantum world, laying the foundations of the quantum era. 

Beyond QKD, Quantum cryptography has applications such as quantum digital signature, quantum random number generator, quantum data locking, etc all of which cumulatively form the quantum internet or the quantum blockchain.

How Quantum Cryptography Can Help The Blockchain


Quantum cryptography is a domain with its limitations and works in progress, but if there is an absolute advantage that is to be outlined over our conventional cryptosystem, it ultimately comes down to security and efficiency. 

Security and efficiency are two of the main technical criticisms of Blockchain. Quantum computers are capable of parallel computing due to the principle of superposition that results in faster computation. Quantum cryptography is provably a secure way to distribute secret keys. And as already stated, the solution to quantum-safe blockchain lies in more research that gives us a pragmatic framework of a cryptosystem that is secure, scalable, and efficient. Experts state that

The ultimate workable framework is likely an amalgamation of PQC & QC with web 3.0. 

Final Thoughts on Quantum Cryptography

Quantum cryptography as a part of quantum information technology promises many technological advancements that seem complex and fictitious as much of this field is still under research and development. It functions on the principles of quantum mechanics and provides information-theoretic security, unlike the traditional cryptosystem that is based on complex math problems and is vulnerable to quantum threats. 

Quantum cryptography is a matured technology that is in rivalry with blockchain tech, but studies show that the ultimate amalgamation of quantum cryptography with blockchain is inevitable

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Karkuzhali Selvarajan HackerNoon profile picture
by Karkuzhali Selvarajan @karkuzhali.Postgraduate Theoretical Physicist. Science Enthusiast. Also interested in inducing existential blues, haha.
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