Community Release - Author: John Ma

Introduction

Quantum computers have powerful computing power and can solve complex operations much faster than conventional computers. Some experts estimate that quantum computers could break encryption in just minutes, whereas the fastest computers today would take thousands of years. As a result, most current digital security infrastructure may be affected, including the cryptography mechanisms that cryptocurrencies such as Bitcoin rely on.

This article will introduce the differences between quantum computers and conventional computers and explain the risks that the former brings to cryptocurrency and digital infrastructure.

Asymmetric encryption and Internet security

Asymmetric encryption is also called“ "Public key cryptography" is an important component of the cryptocurrency ecosystem and much of the Internet infrastructure. Its operating principle is to rely on a pair of keys to encrypt and decrypt information - the public key is responsible for encryption, and the private key is responsible for decryption. In contrast, symmetric encryption uses a single key to encrypt and decrypt data.

The public key can be shared at will, and the encrypted information can only be decrypted by the corresponding private key, ensuring that the information is only open to the designated recipient.

One of the advantages of asymmetric encryption is that it facilitates the exchange of information without having to share keys through unreliable channels. Without this element, basic information security on the Internet cannot be achieved. For example, the concept of online banking based on the inability of untrusted parties to securely encrypt information is simply fanciful.

For more information, please read "Comparison of Symmetric Encryption and Asymmetric Encryption".

Part of the security mechanism of asymmetric encryption relies on a major premise, that is, the algorithm for generating key pairs significantly increases the difficulty of deriving the private key from the public key, and deriving the public key from the private key. The key is relatively simple. Mathematically, it is called a "trapdoor function" - it is easy to calculate in the forward direction, but difficult in the reverse direction.  

Currently, most modern algorithms for generating key pairs are based on the known mathematical trapdoor function. Cracking these trapdoor functions requires huge amounts of computing power and takes a long time. Even the most powerful computers available today take a significant amount of time to perform calculations.  

However, if quantum computers are successfully developed, the situation will greatly change. In order to fully understand why quantum computers are so powerful, we must first understand how conventional computers work.  

Classical computers

The computers we currently know can be called "classical computers". The operations of a classical computer are performed in sequence. After one operation task is completed, the next one can start. The reason is that the memory of a classical computer must obey the laws of physics and can only be in a state of 0 or 1 (off or on).

Through various hardware and software methods, computers can break down complex operations and ultimately improve efficiency. However, the essence cannot be changed. Computational tasks must be performed one by one in order.

Let’s take an example: the computer needs to guess a 4-digit key. The status of these 4 bits may be 0 or 1. There are 16 possibilities, as shown in the following table:

Classic computers need to guess these 16 possibilities one by one, one guess at a time. This is like using 16 keys to open a lock. Each key needs to be tried once. If the first one doesn't open, try the next one until the lock is unlocked.

As the password length increases, the number of combinations increases exponentially. In the above example, if the key length is increased to 5 digits, there will be 32 relevant combinations. Increase to 5 digits, and there will be 64 types. Increased to 256 bytes, the number of combinations is close to the estimate of atoms in the observable universe.

However, the computing speed of classical computers can only increase linearly. Doubling the computing speed can only double the number of guesses in a given time, and this linear increase lags far behind the exponential increase in the number of combinations.

According to estimates, it would take a classical computer system thousands of years to crack a 55-bit key. For reference, Bitcoin recommends using a mnemonic phrase of no less than 128 bits, and many wallets even require 256 bits.

It seems that classical computers cannot threaten the asymmetric encryption used by cryptocurrencies and Internet infrastructure.

Quantum Computer

There is a class of computers that are in their early stages development stage. After the technology matures, it will be easy to solve the problem in the above example - this is a quantum computer. It focuses on the behavior of subatomic particles, based on fundamental principles stated in the theory of quantum mechanics.

In classical computers, information is represented by "bits". The state of a bit can be 0 or 1. Quantum computers also have corresponding units—qubits. It is the basic unit of information for quantum computers. Like bits, qubits can have a state of 0 or 1. However, the unique phenomenon of quantum mechanics determines that the state of a qubit can be 0 and 1 at the same time.

For this reason, many universities and private companies are actively involved in the research and development of quantum computing. They invest a lot of time and money in the hope of overcoming abstract theoretical and practical engineering problems in this field and breaking through the frontiers of human science and technology.

However, quantum computers also have "side effects": quantum operations can easily crack the basic algorithm of asymmetric encryption, fundamentally endangering all systems that rely on asymmetric encryption.

Let’s return to the 4-digit key cracking example in the previous section. Theoretically, a 4-bit quantum computer can test 16 combinations at the same time and complete the task in a single operation. In this operation, the probability of finding the correct key is 100%.

Anti-quantum cryptography

Quantum computing technology can easily break through the cryptographic defenses of modern digital infrastructure, and even cryptocurrencies are not immune.

From individual users to governments and multinational corporations, security, operations and communications around the world will be affected. Of course, R&D institutions and personnel will not "just sit still" and are intensively investigating and developing countermeasures. Encryption algorithms that can withstand quantum computers are called "quantum-resistant encryption algorithms."

Fundamentally, we can easily reduce the risk of a quantum computer breaking the key through symmetric encryption simply by increasing the key length. In order to avoid the security risks of sharing keys in public channels, asymmetric encryption marginalized symmetric encryption and gradually replaced it. However, the development of quantum computing may bring renewed attention to the latter.

The security problem of sharing public keys in public channels is expected to be solved by quantum cryptography. Progress has been gradually made in the field of counter-eavesdropping. Using the same principles used to develop quantum computers, we can detect eavesdroppers on public channels and determine whether a shared symmetric password has been accessed or tampered with by a third party.

In addition, other means of resisting quantum attacks are also being developed. The use of basic techniques such as hashing to create large messages and methods such as lattice cryptography are effective means. The goal of all this research is to find types of encryption that would be difficult for quantum computers to break.

Quantum computers and Bitcoin mining

Bitcoin mining also uses passwords learning mechanism. Miners compete to solve cryptographic puzzles and earn block rewards. If a miner uses a quantum computer, he can dominate the entire network. The network loses its decentralized characteristics and is extremely vulnerable to 51% attacks.  

However, some experts believe this is not an imminent threat. Application specific integrated circuits (ASICs) can mitigate the effectiveness of such attacks, at least for the foreseeable future. In addition, if multiple miners use quantum computers, the risk of attacks will be significantly reduced.

Summary

With the continuous development of quantum computers, asymmetry It seems that it is only a matter of time before encryption is impacted. Let us not worry about it for the time being. There are still huge theoretical and engineering issues to be overcome in this field.

Information security is about to face a huge threat. Everyone should be prepared and actively respond to future attacks. Fortunately, many people are working on how to deploy countermeasures to existing systems. In theory, these countermeasures would protect critical infrastructure from the threats posed by quantum computers.

Just as end-to-end encryption is fully implemented in common browsers and messaging software, quantum-resistant standards can be widely deployed in the public domain. Once standards are established, the cryptocurrency ecosystem can relatively easily integrate the strongest defenses against external attack vectors.