When crypto investors discuss quantum computing, they invariably worry about its potential to undermine encryption. Quantum computers alone do not pose such a mortal threat, however. It’s their capacity to exploit Shor’s algorithm that makes them formidable.
That’s because Shor’s algorithm can factor large prime numbers, the security behind asymmetric encryption.
Another quantum algorithm can potentially undermine the blockchain as well. Grover’s algorithm helps facilitate quantum search capabilities, enabling users to quickly find values among billions of unstructured data points at once.
Unlike Shor’s algorithm, Grover’s algorithm is more of a threat to cryptographic hashing than encryption. When cryptographic hashes are compromised, both blockchain integrity and block mining suffer.
One-way hash functions help to make a blockchain cryptographically secure. Classical computers cannot easily reverse-engineer them. They would have to find the correct arbitrary input that maps to a specific hash value.
Using Grover’s algorithm, a quantum attacker could hypothetically find two inputs that produce the same hash value. This phenomenon is known as a hash collision.
By solving this search, a blockchain attacker could serendipitously replace a valid block with a falsified one. That’s because, in a Proof-of-Work system, the current block’s hash can verify the authenticity of all past blocks.
This kind of attack remains a distant threat, however. Indeed, achieving a cryptographic collision is far more challenging than breaking asymmetric encryption.
A somewhat easier attack to pull off using Grover’s algorithm involves proof-of-work mining.
Using Grover’s search algorithm, a quantum miner can mine at a much faster