Blockchain Technology secured by Quantum Mechanics


Today I come back to a more technical and scientific post here at Digital Distributed Asset. This is more of business minded Blog, but I also wanted it to post on technical topics from time to time. I am a Physics Engineer by background. I’ve also had a longtime interest in issues of economics and business generally. And when the two somehow intersect together, my measure of excitement take to an uplift stage. Science and technology aren’t exciting topics very often for the majority of people (for the scientists and technologists as myself, normally we see excitement where others take a struggle to see and feel the same…), but when coupled with the wider economy and business issues it is regarded in altogether different terms.


That for instance is the case with Blockchain technology. This is an exciting technology, being mainly an elegant and complex Software Engineering endeavour. But its business and wider economic applications make it a technology that when it will be better understood by society at large, it will become mainstream and hopefully an engine of innovation and innovative ideas that will resist boredom, and of course be… exciting. 😊


But currently Blockchain technology is still a work in progress. The maturity level isn’t yet of a normal adult (don’t take the human analogy too literally here though…), and of course stumbling blocks abound. One issue of concern is security. Security is normally a very important issue in any Information Technology development. But with Blockchain technology, given its reliance on advanced cryptography, it is critically important. It might seem like a paradox that a technology relying on advanced software precisely designed to be secure, would be the most ripe for insecurity and vulnerability of its frameworks. But that is exactly the case with advanced security software: it is where the focal point of IT security vulnerability may live. Blockchain is no different in this respect, and its broadly open-source and public nature only makes matters even more critical.


MIT Technology Review posted one other of its numerous interesting articles about technological topics. The one I share and comment here today is about Blockchains being in security danger by clever hacking with Quantum Computers. I will assume that readers of this Blog know at least what Quantum Physics is, and that they heard about Quantum Computers, so I skip an explanation here. These computers are several orders of magnitude capable of computational power out of scope by conventional computers. So they may pose a threat to conventional servers secured by conventional cryptography.


A group of Russian scientists and engineers claim to have been able to design and build a quantum blockchain system in which the security is guaranteed by quantum mechanics. They even published a paper in the Arxiv scientific papers repository called Quantum-secured blockchain.


From the MIT Technology Review article:




First Quantum-Secured Blockchain Technology Tested in Moscow:


First some background. Blockchains record a list of transactions in a way that prevents dishonest use, such as tampering or double spending. They allow any computer to keep track of this list by compiling them into a block, which is then encrypted to form a number called a hash.


The encryption process is important. It is an algorithm that is easy to calculate but hard to do in reverse (like factorization). The hash value it produces is a unique property of the block, and any tampering with the records would be immediately obvious because this would change the hash.


New transactions are next gathered together into a new block and added to the existing hash value. This is then encrypted to create a new hash for the new block. This is added to the next list of transactions when they are encrypted, and so on. The result is a chain of blocks that each contain the hash values of all preceding blocks—hence the term blockchain.


The paragraphs above provide an appropriate yet clear overview of conventional Blockchain technology that most people would understand. At the same time serves well to outline where the crucial bit of what the Russian researchers were able to accomplish with their new quantum-secured blockchain:


All the computers that store these blocks regularly compare their hash values to ensure that they are all in agreement. Any computer that does not agree, discards the records that are causing the problem.


This approach is good but it is not perfect. One way to game this system is for a dishonest user to change the list of transactions in their favor, but in a way that leaves the hash unchanged. This can be done by brute force, in other words by changing a record, encrypting the result, and seeing whether the hash value is the same. And if not, trying again and again and again until it finds a hash that matches.


But with Quantum Computers, brute force computations that with a normal conventional computer would be impractical to crack becomes easily a reality.


The security of blockchains is based on the belief that ordinary computers can only perform this kind of brute force attack over time scales that are entirely impractical, such as the age of the universe. By contrast, quantum computers are much faster and consequently pose a much greater threat.


The clever solution proposed by the Russian researchers goes to the heart of the consensus protocol enabling the Blockchain to perform transactions. This concerns the identity of the senders and receivers in a network of many nodes:


Kiktenko and co have a solution that prevents quantum attacks of this kind. Their blockchain technology is subtly different. A transaction between two individuals contains the information about the sender, the receiver, the time of creation, the amount to be transferred, and a list of reference transactions that justifies that the sender has enough funds for the operation.


The next stage uses an algorithm that allows all parties to agree that the list of transactions is honest. (…)

Next, they communicate the information they received from the other parties in the network allowing everyone to see who said what. The parties then share this information in yet another round and so on until they agree that all computers have the same information.


The proof is that it is always possible to reach a consensus in fewer rounds than there are parties, provided that at least two-thirds of the parties are honest. 

But in such a system how can Alice be sure she is receiving information from Bob and vice versa? Without this certainty, it is easy for a malicious user to game the system by pretending to be lots of different users.


Quantum computers/computing enter the stage now:


This is where quantum mechanics comes in. Alice and Bob can verify each other’s identities using a technique called quantum key distribution. This sends information using quantum particles such as photons, which cannot be copied by an eavesdropper without destroying them. In this way, Alice and Bob can be sure of each other’s identity.


So the bedrock of Kiktenko and co’s system is a quantum identification system in which each party can verify the identity of any other in a way that is guaranteed by the laws of physics. This quantum signature is attached to every transactions making it impossible to tamper with.


The setup was tested in a small network of four users. One of these users is made a rogue trying to game the system with double-spending and the quantum system was able to shut down the double-spending transaction enabling the formation of a block containing only legitimate transactions. This was a proof-of-principle that give quantum blockchain systems a stage in future research and development:


And they’ve tested it in a network of four users, one of which is attempting to game the system by double spending. “This protocol eliminates [the] double-spending transaction after the second communication round and permits the formation of a block containing legitimate transactions only,” say Kiktenko and co.


That’s an interesting proof-of-principle experiment that shows how quantum techniques can be used to secure blockchain technologies.


In spite of the promise and optimism, the hurdles in implementing a quantum-secured blockchain remain obstacles of significant difficulty to pass. The number of dishonest nodes assumed by the authors are on the low side of the spectrum and the Internet isn’t even remotely ready for quantum computing technologies’ implementations:


But it is not perfect. In particular, it assumes that fewer than one-third of the parties are dishonest. If more than a third of users agree to game the system, it becomes trivial to do so.


There are also significant technology hurdles in making this system work on a larger scale. Not least of these is the creation of a quantum Internet to allow these kinds of transaction to take place over long distances. That’s a challenge that should be overcome given that it is currently being tackled by researchers all over the world.


But if the future of quantum computers will become a reality – and this is already a development that will not come back in times of impossibility – the need to build systems that will be able to cope with the threat posed by quantum computers will be definitely real. Conventional cryptography and conventional IT security methods will have to find its way out in order to stay viable and in business. Quantum mechanical solutions may well be the only way out:


The threat from quantum computers is certainly real—and not just for blockchain technology. Any information that is currently stored using conventional cryptography will become unsecure as soon as the first powerful-enough quantum computer is switched on.


featured image: First Quantum-Secured Blockchain Technology Tested in Moscow



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