The recent interest in quantum computing, fueled by Google's assertion that a sufficiently powerful quantum machine could compromise legacy blockchains with less effort than previously thought, has sparked concerns among cryptocurrency holders. For XRP holders, experts offer a more nuanced view, suggesting that XRP's architecture may be better equipped to handle the threat than Bitcoin's.

XRP operates on the XRP Ledger, an open-source, decentralized blockchain used by fintech firm Ripple for cross-border transactions. Let's break down the details step by step.

The primary concern with quantum computing is its potential to reverse-engineer private keys from exposed public keys, thereby allowing unauthorized access to funds. Typically, a public key is exposed when a transaction is sent, making account activity a factor in quantum vulnerability, rather than the balance or the duration the address has been held. Recently, a quantum vulnerability audit of the XRP Ledger found that around 300,000 accounts, holding approximately 2.4 billion XRP, have never sent funds and thus have never exposed their public keys, making them quantum-safe by default. However, dormant whale accounts that have transacted in the past and exposed their public keys are at risk.

The audit identified two such accounts holding 21 million XRP, which, although significant, constitutes only 0.03% of the circulating supply. It's worth noting that the vulnerability of these accounts is based on the assumption that they are dormant and have not rotated their keys, a feature available on the XRP Ledger that allows users to change their signing key without moving funds. This 'key rotation' feature is a significant advantage, as it enables users to secure their accounts without exposing their public keys. Mayukha Vadari, a staff software engineer at Ripple, also highlighted the 'escrow feature' as a defense mechanism against quantum risks.

According to Vadari, funds locked in escrow with a time lock are safe due to the logic of the time lock, which prevents withdrawal until a specified time has passed, rather than relying on cryptography. While this protects the funds, the account holding the escrow can still be vulnerable to quantum attacks.

In comparison, the quantum threat to Bitcoin appears more significant due to the large portion of early bitcoin mined using the P2PK format, which directly exposes public keys in transaction outputs. Google estimates that about 6.9 million BTC are vulnerable, equating to nearly 35% of Bitcoin's circulating supply.

Unlike XRP, Bitcoin lacks a key rotation feature, leaving holders with the option to move funds to a new address, but this process temporarily exposes the public key of the old address, making it vulnerable to quantum attacks. Although the risk is still theoretical, it underscores the relative structural vulnerability of Bitcoin holders.

It's notable that Bitcoin developers have initiated proposals to develop quantum resistance, aiming to mitigate these risks in the future.