The recent focus on quantum computing, sparked by Google's assertion that a powerful enough machine could compromise legacy blockchains with less effort than previously thought, has led to a nuanced discussion about the vulnerability of various cryptocurrencies, including XRP and Bitcoin. For XRP, experts suggest its architecture may offer better protection against quantum threats than Bitcoin's.
XRP operates on the XRP Ledger (XRPL), an open-source, decentralized blockchain used by Ripple for cross-border transactions. A key aspect of blockchain technology is the use of private and public keys for transactions.
The private key is used to sign transactions, while the public key is derived from it and used to generate a wallet address for receiving funds. However, a sufficiently powerful quantum computer running Shor's algorithm could potentially reverse-engineer a private key from a public key, allowing it to drain funds from an account. The vulnerability is most significant when a public key is exposed to the network during a transaction. Recently, a quantum vulnerability audit of the XRP Ledger found that approximately 300,000 accounts holding 2.4 billion XRP have never sent funds and thus have not exposed their public keys, making them quantum-safe by default.
In contrast, dormant 'whale' accounts that have transacted in the past and exposed their public keys are at risk, but the audit found this issue affects only a small percentage of the circulating supply. The XRP Ledger's feature of allowing signing key rotation without moving funds provides an additional layer of protection against quantum threats, although it requires users to be active and aware of the need to rotate their keys. Mayukha Vadari, a staff software engineer at Ripple, also pointed out the 'escrow feature' as a defense mechanism, where funds locked with a time lock are protected not by cryptography, but by logic, preventing withdrawal until a specified time has passed.
While this protects the funds, the account itself can still be vulnerable to quantum attacks. In comparison, Bitcoin's exposure to quantum threats appears more significant due to its larger scale and the use of formats like P2PK, which directly expose public keys in transaction outputs. Google estimates that about 6.9 million BTC are vulnerable, equating to nearly 35% of Bitcoin's circulating supply, a much larger figure than XRP's 0.03%.
The lack of a key rotation feature in Bitcoin leaves holders with the option of moving funds to a new address, but this process temporarily exposes the public key of the old address to potential quantum attacks. Although the risk is still theoretical, it highlights the relative structural vulnerability of Bitcoin compared to XRP.