# Blockchain vs Quantum computer

**Aug. 6, 2018**

All of us have long been accustomed to the fact that information is stored in a centralized manner, that somewhere there is such a database that contains all the transactions of banks, a database with information on real estate transactions, etc.

And there is a danger that in such a system, you can wake up one morning and find out that your apartment or car no longer belongs to you. And it can happen not even on the orders of some official or hacker, but simply by changing one of the fields in the database.

*So what to do if such a system carries a threat?*

I think it's worth considering decentralized data storage.

Imagine that if on each computer there is a copy of the same database, with all the transactions and then an attack on one or even several nodes of such a network will not bring any result.

And here is just **BLOCKCHAIN** is the paradigm that offered a way to store distributed registries.

The idea itself is quite simple and probably therefore it is very interesting.

The blockchain itself is a chain of blocks, in each of the blocks information about some transactions and so on is recorded. further blocks are interconnected and all this is stored on different computers and no one can manage such a network.

Then it turns out that blockchain is cool, blockchain will help us stop worrying about the security of our data, because this is a distributed network, moreover it is a transparent network, each of the nodes of this network can take a look at themselves on the computer what transactions were made today, yesterday and so on and moreover this platform can be formed even if we do not know counterparties and can not trust them in advance.

That is, sort of like really welcome to a new world of secure data storage, with full confidence and without any doubt, but in fact it remains a question and let everyone answer for it after reading this article.

First, let's look at what the blockchain is based on in terms of security. On the one hand, these are mechanisms for trusted authentication, that is, we need to know that we are talking with the node whose name we see on our computer and it is provided through electronic digital signatures. The second big block is complex mathematics, cryptographic hash functions, in simple language it is such a complex task that allows you to actually "seal" the block so that in the future no one else can edit it.

You probably heard about bitcoin, ethereum, other crypto currency and heard about mining, so mining is the same mathematical problem, when people are looking for solutions to complex mathematics, and they are looking for them together, spending a huge amount of energy using huge resources. Although the solution of this task does not have a practical meaning in itself, that is, it will not work for useful calculations, for example, for calculating new materials, or for searching, new stars, because the task does not bear any meaning. Because of this, many analysts often say that blockchain, more precisely its implementation of the form bitcoin, resembles a financial pyramid. People are doing some senseless task, and for this they receive money, capitalization is growing, they again make a meaningless task and again receive money and all costs that are being carried out in the mining, they are actually aimed at ensuring safety.

*But is security really achieved, or are there any agents who can break this security?*

In fact, there are such agents, despite the fact that **blockchain** as a technology is very young, even now we see the danger from the quantum computer.

If we are talking about a quantum computer, then let's look at three main directions in its calculations that exist today.

The first of these is the problem of various optimization, **database** search or logistical tasks - this is Grover's algorithm.

The second big class of tasks is to try to simulate the behavior of new substances on a **quantum computer**, for example to find superconductivity at room temperature or a molecule that can cure from an incurable disease.

And the third big block, this is the factorization problem for prime numbers, it sounds complicated, but in fact it is a problem that can be easily solved in one direction and difficult in another, so if you multiply two numbers on any piece of paper, then you can not find the multipliers from the given product even a computer and even a super computer if the number is long enough. Here is a quantum computer such problems can be solved and thus a quantum computer poses a threat to the blockchain. And what is the threat? Look, the factorization of prime numbers is actually a mechanism for attacking those very digital electronic signatures, which means that we can break trusted authentication, which means we can not be sure that we are talking to the node that we need, not the hacker who under it is masked.

The second task is the optimization task of Grover's algorithm - it allows to accelerate the mining, the acceleration of mining is not only a plus, if one is so accelerated that it can count faster than the rest, then he will automatically be able to generate any blocks he wants, including fake ones and in this case it's the collapse whole bitcoin system.

It looks like science fiction, but now we can expect that quantum computers will appear in the horizon of 5-10 years that will already begin to solve useful or "useful" tasks and it is quite possible on the horizon for 10 years, an attack on blockchain can be carried out.

And what, it turns out that the new technology has not had time to turn around properly and immediately bury it?

Oddly enough, one of the solutions exists, it also lies in the field of quantum technologies.

This is the very same quantum cryptography that can not be cracked. Imagine two black boxes, we take individual photons and write one bit for one photon and then we transmit one thing to them, here in this box these photons form further, they go along the fiber, here more fibers of 25 kilometers are wound up and enters another box, here the quantum world is arranged in such a way that it is impossible to consider the state of 1 quantum particle as invisible, even if you have a quantum computer, this can not be done, because here we are protected by nature.

With the help of such a box, these two boxes, or a large number of boxes, you can restore confidence in terms of authentication. Then we will know for sure that we are talking with the right counterpart.

But then there remains the second task, such as an attack on mining. Strangely enough, mining does not need to be protected at all. In fact, there are other algorithms that allow you to raise a blockchain without using mining. For example, the Byzantine consensus is, on the one hand, a simpler system, but it requires that in our network of trusted nodes (about which we know for sure that they are not intruders) should be 2/3 or more. If such a system exists, it can indeed form the right blocks, even if the remaining third will constantly send some misinformation. In conclusion, I want to say that I think blockchain is an incredibly wonderful idea, a very good paradigm in which you can definitely believe, but you do not have to believe it blindly, you have to understand with what tools there everything is implemented in the depths. Now if we believe in this, but not blindly, understanding how and for what they work, then you can invest in blockchain, bitcoin and so on.