Quantum supremacy vs. Cryptocurrencies security - Can Quantum computer expose to attack Cryptocurrency network?

Since Quantum computers emerges, we all got super charged with huge enthusiasm from Industry, academia to all the way social media. But have you ever realized that quantum supremacy exposes us to risk the security, operations, communications of the entire world, from governments and multinational corporations to the individual users. Meaning lets say a criminal equipped with a functional quantum device, can crack any existing banking security, any passcode and any kind of encryption and breach the system and hack any organizations within a second. Because quantum computer can crack encryption that would take the fastest computers of today thousands of years in mere minutes. Specifically, the quantum computer performed a task in 200 seconds that would take the world’s top supercomputer 10,000 years to perform.

Quantum computers not only can breach traditional existing infrastructure within a second but also can breach most secure blockchain network exist till date and digital security infrastructure could be at risk.

The emergence of quantum computing technology could undermine the cryptography that underlies most of our modern digital infrastructure, including cryptocurrencies. Hence, this has re-ignited fears that one day quantum computers will be strong enough to break through top encryption algorithms, which could theoretically cause all cryptocurrencies to be compromised.

This article will give an idea on how quantum computers to impact the cryptocurrencies and digital infrastructure and what risks they pose.

Let’s first start with how does Cryptography Work. Cryptography is an essential part of the blockchain technology and, therefore, is crucial for any cryptocurrency. The modern cryptography consists of various areas of study, but some of the most relevant are the ones that deal with symmetric encryption, asymmetric encryption, hash functions, and digital signatures. Currently most of the public blockchain is based on Asymmetric cryptography (also known as public-key cryptography). Public Key cryptography is a critical component of the cryptocurrency ecosystem and most Internet infrastructure. It relies on a key pair to encrypt and decrypt information — namely, a public key to encrypt and a private key to decrypt. A public key can be freely shared and used to encrypt information, which can then only be decrypted by the corresponding private key. This ensures that only the intended recipient can access the encrypted information. In contrast, symmetric key cryptography only uses one key to encrypt and decrypt data.

Prior I go through why quantum computers can undermine the existing blockchain network, let’s examine how regular computers work first. In a classical computers, a bit is used to represent information, and a bit can have a state of either 0 or 1. Let’s consider the following example, where a computer must guess a 4-bit key. Each of the 4 bits can either be a 0 or a 1. There are 16 possible combinations, as shown in the table:

A classical computer needs to guess each combination separately, one at a time. Imagine having a lock and 16 keys on a keychain. Each of the 16 keys has to be tried separately. If the first one does not open the lock, the next one can be tried, then the next one, and so on until the right key opens the lock. However, as the key length grows, the number of possible combinations grows exponentially. In the example above, adding an extra bit to increase the key length to 5 bits would result in 32 possible combinations. Increasing it to 6 bits would result in 64 possible combinations. At 256 bits, the number of possible combinations is close to the estimated number of atoms in the observable universe. It is estimated that it would take millennia for a classical computing system to guess a 55-bit key. For reference, the minimum recommended size for a seed used in Bitcoin is 128 bits, with many wallet implementations using 256 bits.

So the Classical computers or even super computers are not a threat at all to the asymmetric encryption used by cryptocurrencies and Internet infrastructure. As we have understood that cryptocurrencies are bullet proof secure against classical computers, let examine how a quantum computer can breach the network

Quantum computers work with quantum bits or qubits. A qubit is the basic unit of information in a quantum computer. Just like a bit, a qubit can have a state of 0 or 1. However, peculiarity of quantum mechanical phenomena, the state of a qubit can also be both 0 and 1 at the same time due to Entanglement. When two particles are entangled, they exist in the same quantum state, and change in the state if one prompts its peer to change accordingly, no matter how far apart the two are in physical space. Pairing qubits this way leads to the exponential growth in the quantum computer’s computational power.

Let’s consider the example of cracking the 4-bit key again. A 4-qubit computer would theoretically be able to take all 16 states (combinations) at once, in a single computational task. The probability of finding the correct key would be 100% in the time that it would take for it to perform this computation.

Now lets say, A criminal equipped with a functional quantum device would be able to perform reverse calculations immensely faster, which would enable them to forge signatures, impersonate other users and gain access to their digital assets and eventually hack the cryptocurrency and even can damage the entire blockchain with 51% attack by taking over the process of updating the ledger, manipulate transaction history and double-spend coins.

It is no surprise that a considerable amount of research is being directed at investigating and developing countermeasures to the technology. Cryptographic algorithms that are assumed to be secure against the threat of quantum computers are known as quantum-resistant algorithms. On a basic level, it appears that the risk associated with quantum computers could be mitigated with symmetric key cryptography through a simple increase in key length. This field of cryptography was sidelined by asymmetric key cryptography due to the issues arising from sharing a common secret key across an open channel. However, symmetric key may reemerge as quantum computing develops. There are other avenues of research being investigated to defeat possible quantum-based attacks. These can involve basic techniques such as hashing to create large message sizes or other methods such as lattice-based cryptography. All of this research aims to create types of encryption that quantum computers would find difficult to crack.

We’re at least a decade from quantum computers being able to break blockchain cryptography. However, in order to survive against quantum supremacy, cryptocurrencies will have to moved to more quantum-proof algorithms and also scope out of how will migrate to the new version of cryptography.