Blockchain, as a technology, is based on the merger of two branches of mathematics: cryptography and game theory. Conditionally speaking, cryptography protects the blockchain network from external influences, guarantees the security and validity of the signature of the owner of the asset (secret key) when it is moved. Game theory strategies protect against internal attacks by dishonest players on the network and guarantee the stability of the system.

## A Quantum Threat to the Blockchain

The emergence of “quantum danger” is associated with the emergence of information that a quantum computer is able to affect the “brute force” on the blockchain. This attack lies in the fact that the change in the body of the transaction will not be reflected in the change of the hash. For example, you can retroactively insert the address of another recipient into a transaction, and then select the nonce variable so that the hash remains unchanged. For today’s computers, this is an unaffordable task because of the huge number of calculations.

But a quantum computer is a completely different matter. Theoretically, it is able to perform simultaneous calculations in parallel universes to calculate all possible values of the variable, and then select the desired one.

Moreover, in the case of bitcoin blockchain, we are talking about a variable size of only 4 bytes (8 bits). Another problem may be the calculation of the private key on the public key. These threats can be attributed to external influences. But there is a possibility and internal.

Imagine what would happen if a quantum computer became a mine in the blockchain. In this case, the problem of 51% capacity will become very urgent. A miner using a quantum computer will monopolize the recording of blocks and will be able to control the chain and maintain a particular branch. This is what game theory calls “kill the king” or Grim Trigger. The result of violating such a strategy is chaos, which will eventually lead to the destruction of the system.

### What is Fundamentally Different From a Conventional Quantum Computer

In a normal computer, a unit of information can have two values: 0 or 1. At the level of the signal — on or off. This is called a bit of information. If you present the information as a sphere, the binary notation system that is used in ordinary computers recognizes only the values at the poles of the sphere. Two poles-two values.

In a quantum computer, a unit of information can be at any point on the surface of a sphere. A quantum computer uses qubits. Not only can a qubit be 0 or 1, it can be zero and one at a time, or it can take any value between them.

Mathematical algorithms used for both types of computers are the same, and their implementation is very different. Quantum computing requires its own programming languages, its own operating systems, its own processors and other elements of hardware, and its own specialists.

While all this is under development and research. There are only highly specialized quantum computers and only a few of them in the world. Each quantum computer is unique and there are no universal systems. After a while, everything will be: unification, universal programming languages, high-class programmers and so on.

Read also about cloud mining: That it how to use also the calculator of earnings.

### Protection Options

The emergence of working versions of quantum computers will fundamentally change the world. This will seriously affect cryptography in the state in which it operates now. Therefore, in parallel with the development of quantum technologies is the development of cryptographic information security systems. This also applies to the blockchain.

While we can observe the gradual improvement of cryptographic protection of the block chain and transactions:

- The complexity of encryption algorithms and their use of combinations.
- The use of other mathematical relationships between the public and private keys.
- Development of practical implementations of already known theoretical cryptographic algorithms.
- Creation of quantum blockchain.
- Use of quantum computers for cryptographic protection of information.

### The Complexity of Encryption Algorithms

An example from paragraph 1 can be considered a company QBit. They suggest using the X11 encryption algorithm instead of the SHA-256 that Bitcoin runs on. The new algorithm uses 11 hashing functions and can calculate hashes much faster. The developers claim a reduction of energy consumption and the much higher speed of transaction processing.

This option cannot be considered a solution in the prospect of quantum computers. Moreover, it disrupts the Nash equilibrium on which Bitcoin’s stability is built. Nakamoto believed that mining blocks should be difficult, inefficient and expensive to prevent internal corruption miners.

### The Use of Other Mathematical Relationships Between the Public and Private Keys

Implementation of the second paragraph on this point may be the Quantum Resistant Ledger (BULLDOGS). They suggest USING the xmss (eXtended Mergele Signature Scheme) algorithm to complicate the definition of the relationship between public and private keys.

The scheme uses one-time private keys that are generated each time you want to sign a message. The principle of” one message — one key ” now significantly enhances the security of signing transactions.

Bitcoin developers advise To use a new public key for each message. BULLDOGS went on, but in a similar way.

At the moment, there is no defined algorithm for a quantum computer that allows, like the shore algorithm, to open private keys generated using ECDSA (SHA-256) for Bitcoin. But if there is a method of shore, we can not say with certainty about the impossibility of another algorithm for the quantum computer.

### The Development of New Encryption Algorithms

The most promising for protection against quantum computers now seems to be the algorithms based on multidimensional lattices. You need to know the secret route through the nodes of a multidimensional spatial grid to read the information encrypted in this way. No matter what kind of information it is: private key, transaction or text.

Recently, it was reported that such algorithms are likely to be vulnerable, but then it turned out that this applies to simplified schemes created for a faster encryption process.

### Creating a Quantum Blockchain

The quantum technology of the blockchain is developed by a group of E. O. Kiktenko. The standard system of quantum cryptography of the Swiss firm ID Quantique was used to create it. Which is based on the scheme mentioned above, in which each pair of nodes is connected using a quantum key distribution line.

In fact, the whole thing boils down to a quantum signature tied to each transaction and transmitted in the form of quantum particles (photons). According to the laws of physics, such signals can not be copied listening device. As a result of this impact, they will collapse.

### The Use of Quantum Computers for Cryptographic Protection of Information

Currently, there are too many uncertainties in this topic and the need to use them in the blockchain.

Blockchain is a decentralized system. The appearance of a quantum computer in the network, generating private keys or some other cryptographic things, destroys the basic idea of the block chain.

For the blockchain mission to be preserved, there must be a network of quantum computers connected via quantum Internet.

## Conclusion

“Quantum danger” for the technology was announced and the development of protection against it has already begun.

To date, the task of complicating encryption algorithms. The problem of quantum encryption must be solved tomorrow. And the implementation of quantum blockchain on quantum distributed networks expects its solution the day after tomorrow.

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