Will quantum computers destroy bitcoin?


Will a quantum computer one day appear and use its greatest computational power to mine all Bitcoin and empty all wallets? While some believe this could happen in the long term, others disagree, saying there is no fear for a long time.

Let’s take a look at an article in which two Canadian computer science professors discuss whether quantum miners pose a threat, and if so, what.

The way to follow

The following idea serves as the basis on which the writers formulate their question: If a miner grows too strong, the network may be in danger. You can direct 51% of the attacks if you have the absolute majority, but even if you don’t, you can still deal damage by engaging in “aggressive” or “selfish” mining.

What happens, then, if a miner uses quantum computing to such an extent that their share of the hashrate increases disproportionately?

This is all really basic and has happened before: mining progress accelerates with technological advancement.

It often happens quickly instead of gradually.

Leading processors were replaced by graphics cards starting in 2011 and Asics stopped making graphics cards in 2013.

During these times, the efficiency grows quadratically or exponentially rather than linearly.

Since conventional processors have mostly reached their limits, quantum computers may represent the next big thing.

This shouldn’t be a problem on its own, as bitcoin’s game theoretical principles encourage rational players to be reliable and stay online.

However, a technological leap can be challenging and can open doors for adversarial forces to work irrationally to undermine Bitcoin.

Knowing when it might happen makes sense, therefore.

What needs to happen for traditional Asics to be replaced by quantum computers in Bitcoin mining?

Unsorted Database Search

It is possible to see miners creating a lot using their computational power when talking about bitcoin mining.

They produce random hashes, and if a hash satisfies a set of scarcity standards, the miner discovers a block.

Another term for it would be a brute force attack against the SHA256 hash algorithm.

The miners are attempting to partially reverse a cryptographic hash function, according to the two professors.

It is “equivalent to looking for a checked item in an unordered list of things (an unstructured search)” to do this “partial inversion of a hash function”.

Although it seems like a minor issue, everything else depends on it.

Since quantum computers are limited in what they can accomplish, finding a specific item in an unordered list is one of the few tasks at which quantum computers have been shown to be superior to conventional computers.

A traditional computer has to go through each entry one at a time while performing a brute force attack or scanning a messy database.

It can be compared to a two-dimensional pointer that navigates between objects.

The chance of success approaches 50% once you’ve seen half the tickets.

A traditional computer therefore requires, on average, N/2 operations, where N is the total number of objects that can be processed.

The benefit of quantum computers is this: multiple qubits can simultaneously represent all imaginable variations, since a qubit can be both 0 and 1.

It can be compared to a pointer that points in N dimensions. The answer is already in the qubits if they are in this “superposition”.

However, as soon as you measure, the solution is ruined.

This is the infamous quantum paradox: if you count, you force the quanta into a certain but random state.

The quantum computer therefore knows the answer, but in a cruel twist, when you go to pick it up, it devalues ​​it.

Grover’s formula squares the realistic acceleration

Grover’s algorithm, which was created by Lov Grover in 1996, is a technique for checking the result.

The qubits identify false results and inhibit them by combining various “quantum gates,” which are the operations of quantum computers.

With each iteration, or the so-called Grover iteration, the probability of arriving at the correct answer increases.

The level of complexity in everything is enormous.

But one thing is certain: the Grover method can significantly speed up such searches if the correct number of iterations is used.

Grover only requires n attempts to locate a particular item in an unordered list.

As a result, it is almost four times faster.

Two instances: Both conventional and quantum computers need two trials if there are four objects.

In contrast, a quantum computer is discovered after 2,280 attempts when there are 5,198,400 pieces, but a normal computer must be executed more than two million times.

This difference is significant, particularly for activities with very high N or that are very hard. The so-called quantum advantage is this difference.

One of those jumps that can completely disrupt an ecosystem. at least conceptually.

The quantum advantage is disappearing

Actually, a quantum miner runs into a specific problem: he cannot locate a block until he measures the result, forcing him to stop the operation.

Therefore, you must plan how many iterations you will perform in advance.

The query is challenging. because there are drawbacks to having too many as well as having too few.

More iterations increase the danger that another miner will be faster and the probability that the correct answer will be found.

Conversely, fewer iterations reduce the probability of a legitimate outcome and, as a result, the quantum advantage.

A quantum computer could fully utilize the quantum advantage if it had infinite time. However, mining prohibits it. Between too few and too many iterations, a balance must be struck.

The researchers created a Markov chain containing all the potential outcomes to determine the best tradeoff.

A mathematical representation of potential, largely random, or partially unexpected sequences is called a Markov chain.

Such a string shows which path through the probability maze, or the best setting of Grover’s algorithm, often leads to the best results.

This would take, surprisingly, 16 minutes.

Two notable discoveries

Let’s say it takes a quantum miner 16 minutes to read the output of Grover’s algorithm. When compared to the long-term drawbacks, its benefit over traditional mining is maximum.

Scientists claim that this benefit exists regardless of the challenge.

Because it can be used, the result is quite impressive. Here, two serious results can be seen:

First of all, by using this strategy, the miner excludes himself from about 80% of the blocks. This is the result of things that are discovered in less than 16 minutes.

With the remaining 20%, you increase your chances of success.

The overall mining power that quantum computers should be able to achieve must not exceed this without compromising effectiveness.

Second, the time between blocks is usually shorter for cryptocurrencies. Ethereum and Ripple only have a few seconds, while Dogecoin and Litecoin have a few minutes.

With these blockchains, the quantum advantage is not true, so quantum miners are getting a nosebleed. In mining, they are already quantum safe.

Parallelization of quantum computers also appears to be a dead end.

Grover’s method makes this conceivable, however the authors’ calculations show that it only improves performance by a factor of m.

The element is m for traditional computers, which makes it quadratically larger.

Therefore, it is doubtful that quantum computers are useful for mining.

Megahashes: 78

These calculations already significantly reduce the threat posed by quantum computers.

But the most important question remains unanswered: What must happen before quantum miners gain an advantage over traditional miners?

When, if ever, will a quantum computer be used to find out which block will be less expensive?

The cost per grover iteration and the ratio of hashes needed for a block to the grover iterations needed are the two determining elements in this.

The authors make this calculation using the example of a currently prevalent quantum computer that has a “gate speed” of 66.7 megahertz.

The gates, or quantum processes, are the gates.

According to the researchers’ calculations, this quantum computer could perform 224 Grovers every second.

Sense? A hash rate of 78 mega hashes per second is equivalent to 224 Grover iterations.

That equates to a minuscule portion of the Bitcoin hashrate and is far less than contemporary Asics achieve. It would be absurd to perceive any threat here.

Possibly future versions that are more energy efficient

But are quantum miners at least more productive if they don’t pose a threat? So is it possible to transition to quantum mining, even if only gradually? Also, when?

The energy cost of a Grover iteration only needs to be 3.49 × 105 times that of a conventional hash to be most effective.

A quantum computer would need an efficiency greater than 3.49 x 105 x 10-10, or about ten J at each Grover iteration, to be as energy efficient as traditional miners, which have an energy efficiency of 10-10 joules per minute. hash maybe even 2240 J/s.

That seems really demeaning. However, quantum computers need relatively little power.

The quantum bits transform into a superconductor after the system cools to 15 millikelvins, or near absolute zero, and need almost little electricity and generate almost no heat.

A quantum computer is still uneconomical at the moment due to cooling relative to electricity.

But as technology develops, this should change.

In conclusion, Bitcoin users should rest easy knowing that they are a bit smarter and can no longer imagine the terror of a world run by quantum computers.

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