The short answer is yes, quantum computing does pose a potential threat to blockchain security, however, that’s not the complete answer. For one thing, quantum computers are still in the process of being developed, and none exist just yet.
Also, while the technology has what it takes to disrupt blockchain security, it’s quite possible that by the time quantum computers are manufactured, blockchain technology would have advanced enough that they could counter the new threat.
Cryptographers are aware of the theory behind quantum computing and are already working on developing quantum-resistant systems for better security. To understand what this all means better, we need to backtrack a little and look at each element individually.
Let us take a closer look at why a blockchain is so secure right now and what could happen when quantum computers come into play.
The popularity of blockchain technology has arisen from how secure the network is. Peer to peer (P2P) transactions can be carried out online without the need for a middle-man or regulatory body and can be completely safe. Two aspects that make a blockchain so secure are its decentralization and the use of a public and private key. a blockchain is monitored by nodes that are spread out all across the internet. These nodes keep track of transactions and store them.
The nodes are constantly in communication with each other and ensure that they all have the same information. Every time a new transaction is carried out, the information is stored in a block. A node can verify whether the block is valid or not and accordingly, accept or reject it. Accepted blocks are stored on top of existing blocks and get added to the chain. Immediately, all other nodes on the network get updated with the same information.
All transactions carried out on a blockchain require a public and private key. The public key allows the nodes to verify the transaction, while the private key keeps the transaction secure between the two parties involved. Private keys are derived from complex mathematical formulas and are impossible to crack at the current computing potentials.
Compromising a Blockchain
To compromise the security of a blockchain, a hacker has to either decrypt the private key or hack at least 50% of the nodes simultaneously. Both of these methods are virtually impossible at the current speed and computing power of existing computers. But, in theory, they are not beyond the scope of a quantum computer. Estimates have put quantum computers at 100 million times faster than the computers of today.
Shor’s algorithm is a quantum algorithm which when run on a quantum computer has the potential to crack private keys in a fraction of the time it would take now. Hacking multiple nodes simultaneously will also be possible with quantum computing. Where classical computing uses a binary system of ones and zeroes, quantum computing uses qubits which can exist in the values between 0 and 1. This system allows them to store much more information and be much faster than existing computers.
Ultimately, quantum computing can pose a threat to a blockchain, but the technology is yet to be fully developed.