The Quantum Threat to Blockchain
We are in the midst of multiple technological revolutions, however, two of these technologies could potentially be at odds. Blockchains are decentralized networks that are much more tamper-resistant than their centralized counterparts. Quantum computers are a paradigm shift in information processing and are much more powerful than their classical counterparts. They also have the potential to break various algorithms that are commonly used in cryptocurrencies.
What is Quantum Computing?
Computers have worked basically the same way since their invention many years ago. They encode information in bits, whose value can be either 1 or 0. This way of encoding is commonly known as binary. In computers these are represented by electrical signals and transistors. When used individually, they don’t mean a lot. However, when used in long strings, they represent answers to complex problems.
A quantum computer runs on quantum bits, or qubits. These are tiny particles suspended in extreme cold, near zero Kelvin. This is to reduce the total entropy in the system, or unwanted “noise”. The idea is to keep these particles in a state of superposition so that they can be simultaneously 1 and 0. Qubits are therefore able to process much more information at once.
Although much of this may sound like science fiction, the race to build quantum computers has already begun and industry giants like IBM, Microsoft, Google, and Intel are at the forefront. Recently, IBM unveiled a 50 qubit universal quantum computer capable of keeping its quantum state for 90 microseconds. This may seem like a very short amount of time, but it is a major step forward for the development of these systems.
A Canadian based quantum computing company called D-Wave Systems, which partners with Google, showed that its quantum annealing computer is 100 million times faster than its digital counterparts at certain tasks. Although D-Wave’s computers run a different type of architecture which does not lend itself well to the types of algorithms that pose a threat to blockchains, it shows just how powerful this new type of computing can be.
Cryptography on the Bitcoin Blockchain
In order to make sense of the threat that quantum computing could potentially pose to blockchain technology, let’s take a look at how the security protocols work in the bitcoin blockchain. Bitcoin’s protocol, like most cryptocurrencies, involves two types of cryptography, the hash functions used in the mining process, and asymmetric cryptography used to provide digital signatures on the blockchain.
Miners use their computing power to calculate a nonce for each block using the SHA-256 hash algorithm, a process whose solution is easy to verify, but difficult to find. Asymmetric cryptography is used to authorize transactions on the bitcoin blockchain. Each user is assigned a public key and a private key. As the names suggest, the public key is available to everyone and is how other people on the blockchain can transact with you. The private key gives a user ownership of the bitcoin stored at the address. For example, if Alice wants to send 5 bitcoins to Bob, Alice will first use her private key to unlock the 5 bitcoins sent to her by someone else, then she will send the coins to Bob’s public key. So can quantum computers crack both of these types of cryptography?
As it stands, if a miner controls more than 50% of the collective computational power on the blockchain, they can act maliciously, altering the blockchain to their heart’s content. So if a quantum computer comes online, will the user be able to carry out this type of attack? Divesh Aggarwal and researchers from the National University of Singapore (NUS) looked into the threat that quantum computers pose to the bitcoin blockchain. Their conclusion? The use of application-specific integrated circuits (ASIC) commonly used in bitcoin mining will likely maintain a speed advantage to quantum computers at least for the next ten years.
So it seems that mining on the bitcoin blockchain is quantum-proof, at least in the near future. However, Aggarwal and his team believe that the main vulnerability in the bitcoin protocol is the asymmetric cryptography algorithms that the blockchain employs, the public key infrastructure. This infrastructure uses something called the Elliptic Curve Digital Signature Algorithm (ECDSA) to generate keys. Given a private key, it is easy to derive the corresponding public key, however, going in reverse is computationally difficult. This is what makes the bitcoin blockchain secure… for now. The researchers at NUS note that with the use of quantum computers, it would be easy to run the process in reverse to generate private keys from public keys, effectively revealing everyone’s private keys.
On the other hand, the elliptic curve signature scheme used by Bitcoin is much more at risk, and could be completely broken by a quantum computer as early as 2027, by the most optimistic estimates. — Divesh Aggarwal
It is important to note that this problem is not unique to blockchains. Other technologies that use similar encryption methods are also at risk. In fact, much of the internet relies on encryption algorithms like ECDSA that would also have to be revised when quantum computers become more commonplace.
Post-Quantum Technology
So does this mean that bitcoin is doomed? Probably not. The NSA has announced that it has recently been working on cryptographic systems that are resistant to attacks from quantum computers. The blockchain community has also thought about future-proofing their systems. The Quantum Resistant Ledger is a project that uses the Extended Merkle Signature Scheme which the team says is much more secure than ECDSA and can protect the blockchain from unforeseen advances in quantum computing.
The nature of technology is that progress in one field tends to have a ripple effect across other fields. With advancements in quantum computing, it’s clear that blockchains and other systems that rely on modern cryptography will have to adapt, but the threat is far from immediate. The good news for blockchains is that they lend themselves well to upgrades, and have passed the test of time, lasting approximately ten years with no major hacks to the protocol. If this is any indication of the resiliency built into these systems, it is a good sign that they will last well into the future.
To read Divesh Aggarwal and the NUS team’s full analysis, click here
Image Links:
