Blockchain, a promising technology shows considerable transformative potential. Many experts consider its features like data security and immutability very important. However, several experts believe that quantum computing can undermine these features of blockchain. In this article, we analyze the likelihood of this. We discuss the relevant features of blockchain, e.g., data security and immutability. We look at quantum computing and how it might impact blockchain. Finally, we look at efforts to create a quantum-resistant blockchain.
What does blockchain offer?
We use the example of Bitcoin to describe what blockchain offers. A public blockchain network like Bitcoin offers the following:
Decentralization: It’s a peer-to-peer (P2P) network, and the computers on this network are called “nodes”. It doesn’t have a central administrator. All nodes have equal authority.
Distributed ledger: The entire data is replicated in all the nodes. Every node on the network has the entire ledger of all transactions. One can’t shut the Bitcoin blockchain network down by just shutting down one node.
Security: Users need to sign their transactions on the Bitcoin blockchain network by using their digital signatures. They keep their data secure by just securing their private key.
Transparency: All participants in the Bitcoin network can see all transactions.
Data integrity: The Bitcoin blockchain network stores transaction data in blocks. Blocks are data structures. Techniques like cryptographic hash function and consensus algorithms ensure that new blocks can be created only after verification.
Immutability: Cryptographic hash functions and consensus algorithms also ensure that no one can modify or delete existing blocks.
The significant promises of blockchain continue to drive its market. A MarketsandMarkets report projects that the global blockchain market will grow from $3.0 billion in 2020 to $39.7 billion in 2025.
How do the security, data integrity, and immutability features of blockchain work?
We now talk about the working of the security, data integrity, and immutability features of blockchain.
Security, thanks to digital signatures!
Bitcoin users have their digital signatures. They need to sign a transaction using this signature. Bitcoin users have their public key, which is their public address. They broadcast it publicly. Others can send digital currencies to this address.
Bitcoin users also have their private keys. They should secure it since it’s supposed to be secret. The public and private keys are linked to each other via public-key-private-key cryptography. One can find the public key easily from the private key. However, it’s extremely hard to find the private key from the public key.
Why is it so? That’s because public-key-private-key cryptography uses integer factorization to link the private key with the public key.
Let’s talk about integer factorization with an example. Consider the number 162. You can express it as (2x3x3x3x3). Therefore, the two prime factors of 162 are 2 and 3. You could find this easily. Your computer will be able to find it easily enough. That’s because 162 is a small number.
What happens when you take an exceptionally large number? You will take a very long time to find its prime factors. Your computer will take a very long time too!
Public-key-private-key cryptography uses numbers so large that today’s computers might take billions of years to find their prime factors! That makes cracking digital signatures very hard indeed!
Data integrity, thanks to cryptographic hash functions and consensus algorithms!
How does the Bitcoin blockchain network prevent the creation of a block in the wrong way? Transaction validators on the Bitcoin blockchain network are called “miners”. The transaction validation process is called “mining”.
Miners try to create a new block, which will have the cryptographic hash of the earlier block. The mining process involves rewards, therefore, it’s a competitive process.
Miners try to solve a cryptographic puzzle to create a new block. It’s a moderately difficult puzzle, however, it’s not impossible to solve.
Solving this puzzle doesn’t require skills. Miners need to key trying one number after another. They need to run this process at a high speed. They need computers with high processing power, and they run up considerable energy bills.
A miner broadcasts the answer to the network after finding the answer to the puzzle. All other miners see this evidence. This is why this consensus algorithm is called the “Proof of Work” (POW).
The Bitcoin network is large, and there are many miners. Malicious actors can’t manipulate other miners on this network. Malicious powers could try to overpower other Bitcoin miners, however, they need to control over half of the total computing power in the Bitcoin network. That would require huge computing power. Today’s computers can’t provide that.
Immutability, thanks to cryptographic hash functions and consensus algorithms!
Bitcoin is digital money, and it has no physical presence. One Bitcoin transaction is a transaction on a computer. As we know, hackers tamper with data on computers. They can tamper with a past Bitcoin transaction and divert the fund to another address. We would call that “double spending”, and the Bitcoin network needs to prevent that. How does it do that?
Take the example of a hacker trying to change a transaction in the 25th block of the Bitcoin blockchain. As soon as hackers change the data, they need to recreate the cryptographic hash of the modified block.
A cryptographic hash function always creates a different hash when the input data undergo even a minor change. The 26th block has the hash of the 25th block. Hackers then need to change the 26th block to incorporate the new hash of the 25th block. That changes the data in the 26th block! Hackers need to keep changing one block after another, and all participants in the network can see that.
Hackers need to do all of these manipulations extremely fast. They also need to overpower the computing power of the entire network so that they can manipulate all other miners. Today’s computers don’t provide enough processing power for that.
Quantum computing: What it is
A public blockchain like Bitcoin can offer a high degree of security, data integrity, and immutability since today’s computers can’t break its security solutions. Quantum computers might change that. They will likely have far more processing power than today’s computers.
We won’t explain all aspects of quantum computing here since it’s not quite in the scope of this article. We will only discuss the aspects relevant to our question of whether quantum computing can break blockchain.
As IBM defines, quantum computing “harnesses the phenomena of quantum mechanics to deliver a huge leap forward in computation to solve certain problems”. Paul Benioff, a physicist had started to work on quantum computing in 1980.
A quick recap of the evolution of the quantum theory in physics
Quantum theory in physics evolved as follows:
• Max Planck, a renowned physicist stated in 1900 that energy has units just like matters have particles. Planck called these units “Quanta”.
• In 1905, Albert Einstein stated that radiation has similar quantifiable units too.
• Louis de Broglie formulated the “Principle of wave-particle duality”. He stated in 1924 that matter and energy behave similarly at a fundamental level.
• Werner Heisenberg formulated the “Uncertainty Principle” in 1927. Heisenberg stated that if we try to precisely measure two complementary values like the position and momentum of a subatomic particle, then that act of measuring one will change the other.
“Qubit” in quantum computing: The use of the “Principle of wave-particle duality” in computing
Computing as we currently know uses “bit” as the smallest unit of storing information. A bit can have either a “0” or a “1”.
Quantum computing uses “Qubit” as the smaller unit of storing information. A Qubit can hold a “0”, a “1”, and a superimposed state of both, simultaneously. It uses the “Principle of wave-particle duality” in computing.
This materially alters the computing paradigm. Qubits allow quantum computers to have far more processing power than today’s computers.
How could this impact the Bitcoin blockchain network? Malicious actors can potentially get access to a quantum computer. They can join the Bitcoin blockchain network. The massive computing power of their quantum computer will give them over half of the total computing power on the Bitcoin network. They can then overpower other miners and manipulate the working of the consensus algorithm.
“Shor’s algorithm”: A polynomial-time quantum algorithm
Peter Williston Shor, an American professor of applied mathematics at MIT is well-known for his work on quantum computing. He had developed a polynomial-time quantum algorithm in 1995. This algorithm came to be known as the “Shor’s algorithm”.
This algorithm can solve a large prime factorization problem in a very less number of operations than classical algorithms. As a result, a quantum computer running the “Shor’s algorithm” can solve such a prime factorization problem in a few days. That’s significantly different from the capabilities of today’s computers.
How does this impact the Bitcoin blockchain network? Hackers with a quantum computer can break the public-key-private-key cryptography in the digital signatures used by Bitcoin users. They can then submit transactions by digitally signing them on behalf of the original users.
When will quantum computers break blockchain?
The research on quantum computing started in 1980. It’s still under research and development. Experts say that quantum computers will have significant use cases in fields requiring large-scale number-crunching at speed. Quantum computers might make a significant difference in cybersecurity, weather forecasting, pharmaceutical R&D, etc.
National governments of countries like the USA, China, and India are trying to develop quantum computers. Technology giants like Google and IBM are developing their quantum computers too. These organizations have made progress in their efforts. However, knowledgeable observers can’t quite say when quantum computers will be available commercially.
The general launch of quantum computers might take more than a decade. Blockchain networks don’t face an immediate threat yet from quantum computers.
A few efforts to create quantum-resistant blockchain networks
The investments in blockchain will lose their relevance if quantum computers break blockchain networks. Many researchers, experts, and developers are already working to secure blockchain from quantum computers. A few examples are as follows:
The Quantum Resistant Ledger (QRL)
A blockchain project team has developed The Quantum Resistant Ledger. The project team has implemented several post-quantum data encryption algorithms.
The team calls its solution the “eXtended Merkle Signature Scheme” (XMSS). This solution utilizes OTS (One Time Signature), which allows users to sign only one transaction with one key. This solution doesn’t involve a private key, therefore, hackers with quantum computers don’t have anything to hack!
The “quantum-safe” blockchain from a team of Russian researchers
In 2017, researchers at the Russian Quantum Center announced the creation of a quantum-safe blockchain. They combined post-quantum cryptography with quantum key distribution (QKD).
QKD uses laser beams to transmit cryptographic keys. This involves using the quantum properties of photons. The “Uncertainty Principle” formulated by Heisenberg takes over from here!
Hackers trying to intercept the cryptographic keys will need to observe subatomic particles. The very act of observing changes the quantum properties of these particles. The interception attempts by hackers make the cryptographic keys unusable!
A blockchain network using quantum entanglement
Del Rajan and Matt Visser, two researchers at the Victoria University of Wellington, New Zealand proposed a blockchain network that will use quantum entanglement. Their idea involves creating a blockchain using quantum particles. These particles are entangled in time.
One quantum particle can encode the history of all of its predecessors. Assume that hackers are trying to hack one such predecessor particle. That very act will destroy that particle. The blockchain remains though since the last particle has the entire history of the blockchain encoded.
Blockchain offers robust security, data integrity, and immutability. The limitations of today’s computers make it impractical to hack blockchain networks. Quantum computers will have much more processing power. They might break blockchain, and we reviewed these possibilities. We also reviewed efforts to build quantum-resistant blockchain networks. Watch this space for more exciting news on the quantum computing subject!