There are actually a few different ways a quantum computer can snap a blockchain.
For one, blockchain transactions are secured with digital signatures based on elliptic curve cryptography (ECC). ECC coincidently is also used on the internet to encrypt user data and website traffic.
However, ECC is not “quantum-safe,” according to Post-Quantum’s Cheng, meaning that a powerful quantum computer could theoretically decrypt user private keys and forge transaction signatures on their behalf.
“Once that trust is broken, that will be the end of cryptocurrencies,” said Cheng, adding:
“If you can no longer tell whether [the right] people are signing transactions to you or not, then you have destroyed trust. This cryptocurrency world is based on a distributed, trustless environment.”