What Quantum Computers Mean for the Future of Blockchain
Bitcoin-mania may have passed but the blockchain revolution it kicked off is quietly humming away. Financial institutions, governments, and start-ups are all finding innovative ways of using blockchain to build fairer, more robust systems.
However, some observers are now concerned that it could all be undone by another groundbreaking advance: quantum computers.
Harnessing the power of quantum computing will help propel humanity into the next stage of its evolution. Quantum computers draw on the almost mystical properties of quantum physics in order to process vast amounts of data at an unprecedented speed.
An excellent quantum computing explainer for the uninitiated
Instead of relying on 1s and 0s (bits) to represent data, quantum computers are able to use a qubit, a two state quantum system. This allows a quantum computer to process a large number of different outcomes simultaneously, rather than being forced to process a huge string of binary code. Quantum computers are designed to capture and contain qubits in a stable state and then leverage two important aspects of quantum mechanics to process large amounts of data.
Superposition: Qubits can hold all possible combinations of 1 and 0 simultaneously. This allows a quantum computer with multiple qubits to process a large number of different outcomes simultaneously. As a quantum computer holds more qubits, its processing power grows exponentially.
Entanglement: Quantum Computers can generate qubits that are entangled, this means that it is possible to change the state of one qubit and predictably alter the states of other qubits that it is entangled with. This allows running multiple calculations simultaneously, squeezing more processing power out of a single qubit.
The potential applications of quantum computers are incredible. We are collecting more data than ever before and quantum computers are perfect for processing it. This is particularly true when it comes to research projects that require understanding multiple outcomes, such as predictions or simulations.
As quantum computers grow in power it will become easier for us to process increasingly complex simulations. This will have extra effects in countless sectors and fields of study, rapidly accelerating human progress.
The same properties that make quantum computers excellent for research make them a major security threat. Your entire online life could be endangered by quantum computers: from your passwords to your whatsapp messages and even to your online banking. This is all dependent upon cryptography, which is the same technology that powers blockchains and cryptocurrencies.
There are three main kinds of cryptography:
Symmetric-Key Cryptography: Both the sender and receiver use a single key. The sender encrypts plaintext and gives the ciphertext to the receiver. The receiver can apply this key to decrypt the message and recover the plain text. This is one of the oldest forms of encryption and is relatively rudimentary.
Public-Key Encryption: One of the major advances that makes blockchain technology viable. Two related keys, the public key and private key, are used. The public key can be shared without revealing the identity of the private key. The public key is used to encrypt the data and only the private key can decrypt it.
Hash functions: A fixed-length hash value is computed which makes it difficult to recover the contents of the plain text without brute-forcing it using sheer computing power. This is often used to encrypt passwords and also for cryptocurrency.
All cryptography relies on mathematics to protect it. Without the correct key, computers are forced to process incredibly complicated calculations. This means it could take years, or even centuries, to brute force a properly encrypted file. This is also the basis of Proof of Work cryptocurrencies like Bitcoin and what helps to secure them.
The vast processing power of quantum computers could render this protection worthless overnight. It would be theoretically possible for bad actors to rip away the protection of encryption and reveal the contents of a file without the key. This would be particularly dangerous for blockchains as a quantum computer would then be able to process fraudulent transactions or data.
The threat is likely still in the distance. Decoherence means that even small changes in temperature, slight vibrations, or other variables can cause a quantum computer to break down. This means that for the moment they are not viable and this gives cryptographic experts and blockchain companies time to prepare.
In the general cryptography world, the main effort is towards building quantum-proof cryptography. The NIST launched a competition in 2016 to develop new standards in cryptography and while the winners have not yet been announced, a consensus seems to be forming around the best approach: lattice-based cryptography.
Instead of using traditional math to encode data, lattice-based cryptography uses grids with billions of individual points across thousands of dimensions. Breaking the code would require finding the correct path from one specific point to another, which is difficult without the map or key. It's important to note that the keys required to unlock lattice-based cryptography would need to be small enough to be practical in real-world use.
For blockchains, there are a few key problems.
The first is user behavior. Novice crypto users, or those engaging in proof of stake (PoS) blockchains, often reuse one wallet address. This means that a quantum computer could use the public key to find and break the private key, stealing the contents of the wallet. The second threat is that quantum computing could be used to more easily cause a 51% attack on proof of work (PoW) blockchains.
Particl and Cold Staking
Proof of stake Relies on users “locking” a specific amount of their currency in order to secure transactions on the blockchain. It is less energy-intensive than proof of work. Unfortunately, most forms force a user to reveal their public address to gain access. Given that most people will be keeping their coins in a single wallet, this is a huge security flaw.
The solution is something called cold staking used by Particl. This approach leverages multi-signature addresses so you can stake from multiple computers. Users would then be able to spend their money through a mobile wallet.
As the stake-only machine is broadcasting a public key different from the mobile wallet key, it is almost impossible to link the private and public keys. In order to steal coins an attacker would need to know both keys, which requires more than a quantum computer.
PoW remains one of the most popular consensus methods, and is the one used by Bitcoin itself. For the moment, quantum mining is unlikely to be profitable but a bad actor may have motivations other than profit.
In order to fully protect from the threat of quantum computers, projects like the Quantum Resistant Ledger (QRL) have sprung up. The QRL is the first industrial implementation of the eXtended Merkle Signature Scheme (XMSS). This hash-based signature scheme is more advanced than ECDSA and should be significantly more difficult for a quantum computer to crack.
The big challenge for cryptography specialists and blockchain developers is that cryptography moves slowly. It can take 10 or 20 years to standardize or implement new cryptographic algorithms into products. If moves aren’t taken now, the cryptographic community could find itself unprepared for the quantum future.
Written by the Rebellion Team & Edited by Calvin Ma, Gihyen Eom & Alexander Fleiss