How Blockchain consent mechanisms can resist quantum computers

The quantum calculation is extremely powerful and could theoretically dominate the mining networks. How can blockchain resist this level of consent?

Quantum computers are on track to become a force that should not be underestimated and cryptography is one of the areas where the first quantum computers are applied. This fact has serious implications for the blockchain technology, which is based on cryptography in various ways.

In the first part of this two-part series on quantum computing and blockchain, we discussed how quantum computers could be used to decipher the cryptographic schemes currently used to protect cryptographic addresses. Although this is the most urgent concern, it is only one way quantum computing could affect the safety of the blockchain.

Cryptography is also an integral part of proof-of-work and other blockchain consent mechanisms. While encrypted addresses store value and must be impossible to break, the work trial algorithms are limited to making use of hard cryptographic problems to drive competition between miners.

Miners can solve these problems to gain symbolic prizes and gain partial control over a blockchain. At the moment, hundreds of thousands of Bitcoin miners compete on the network, which means that no one has significant control over the Bitcoin blockchain.

This achieves decentralization: countless blockchain participants work independently, but collectively form a system that is safe and generates value. However, a fairly powerful quantum computer could theoretically dominate a large mining network alone.

Fortunately, there are many factors that will prevent this from happening in the real world. Let's take a look at how some different consensus mechanisms handle the threat posed by quantum computers.

Work-proof blockchains like Bitcoin use mining networks to generate value. Each node or miner is responsible for solving a problem or a cryptographic puzzle. Discovering a solution involves testing different inputs that could produce a given hash. It is said that the most powerful computers have a higher hashrate: they solve more puzzles and hash more blocks.

Quantum computers with sufficient power would be able to test many different solutions simultaneously, allowing a quantum computer to solve problems quickly. If a quantum computer could solve problems more efficiently than half the mining network, it could perform a majority attack. At first glance, this is plausible: quantum computers are exponentially faster than traditional computers.

However, there are some reasons why quantum computers are unlikely to do such an attack on a mining network. First of all, someone should program a quantum computer to extract Bitcoin more efficiently than traditional ASICs and computers. This is not a trivial task, and quantum computers will not outperform traditional computers in many areas for years or decades.

Moreover, when quantum computers generally become useful, they are likely to be widely available. In this case, quantum computers would be used by many different nodes on a data mining network and no single quantum computer would pose a threat to the rest of the network.

Although work testing networks can, in theory, be dominated by a powerful quantum computer, other consensus mechanisms do not depend on the raw power of the computer. In these cases, quantum computing poses even less a threat to blockchain consensus.

For example, consent to the stake test distributes control over a blockchain based on the number of tokens that each node blocks in a contract. Although proof-of-stake still requires nodes to do computational work, the probability of a node validating a block depends on the number of tokens they represent, not on their computing power.

This provides a degree of resistance against quantum computers and other powerful mining devices. The book of the Quantum Resistant Ledger has adopted a test consent for the stake for this reason. However, consent to the stake test is used much more widely than this – in particular, it is part of the next Casper protocol of Ethereum.

Consensus on the stake test is already becoming popular because it prevents large-scale mining operations and mining titans (such as Bitmain) from dominating a blockchain network. These giants represent a more imminent threat than quantum computers, although quantum computers are more powerful in theory.

Consent to the stake test is rapidly gaining ground in the blockchain world, but there are other ways to create limits that could protect against quantum dominance. Both of the following approaches provide resistance against today's most powerful mining efforts as well as tomorrow's quantum computers.

One way to approach this is to introduce hybrid consensus mechanisms. For example, the Hcash cryptocurrency, which has a quantum resistance, combines two different types of consensus: proof of work and proof of the stake. This makes most of the attacks not feasible, but keeps mining activity profitable.

There are also much more experimental approaches. For example, IOTA does not allow powerful computers or rich stakers to validate as many transactions as possible. In reality, it does not involve mining or stakeout at all. The basic consensus system is very experimental and it is difficult to say whether a majority attack against the IOTA would succeed or be convenient.

Researchers at the University of Wellington have proposed a blockchain based on quantum mechanics at a fundamental level. This blockchain would encode data on quantum particles and quantum entanglement would be used to create a truly immutable blockchain.

This innovation would change the blockchain technology to a much more fundamental level of the consensus mechanism. The resulting quantum blockchain would also be much harder to attack. The current blockchains are considered immutable, but in reality they are very difficult and expensive to tamper with. A quantum blockchain would be impossible to tamper with due to the laws of physics and the way the weather works.

This solution may seem far away, with good reason: a public blockchain that runs on this system would be based on a network that is very different from what we have today. However, it is one way that blockchain technology could one day make use of quantum technology.

At this point it should be clear that quantum computers do not necessarily represent a threat to most blockchains at the consensus level. The work trial networks, even if susceptible to majority attacks, will probably benefit from the gradual introduction of quantum computers. Other mechanisms, such as the pole test, are even less susceptible to quantum dominance.

However, powerful computers in general pose a threat. Although the major blockchains like Bitcoin and Ethereum are fairly safe, smaller blockchains often become targets for majority attacks. Quantum computing could be used to protect blockchain platforms in ways that have never been seen before, although it will take time to implement these innovations.