The emergence of quantum computing has sparked concerns about the security of legacy blockchains, with Google suggesting that a powerful enough machine could compromise them with relatively less effort. For XRP holders, the outlook is more nuanced, with experts suggesting that the architecture of XRP is better equipped to handle this 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 threat to blockchains comes from the potential for a sufficiently powerful quantum computer to reverse-engineer private keys from exposed public keys, thereby draining funds. Typically, a user's public key is exposed when they send a transaction, and their wallet address is generated from this public key.

However, XRP's design includes features that mitigate this risk. Recently, a quantum vulnerability audit of the XRP Ledger found that approximately 300,000 accounts, holding around 2.4 billion XRP, have never sent funds and thus have never exposed their public keys to the network, 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 these accounts hold only about 0.03% of the circulating XRP supply. The XRP Ledger's account-based system and the ability to rotate signing keys without moving funds are key features that enhance security.

This 'key rotation' feature allows users to change their account's signing key without having to move funds, effectively changing the 'lock' on their account without moving it. Experts like Vet highlight that while this feature is available to all users, the problem lies with long-dormant accounts whose owners may have lost their keys or are no longer active.

Mayukha Vadari, a staff software engineer at Ripple, points to the 'escrow feature' as another defense mechanism. Funds locked in escrow with a time lock are safe due to logical constraints rather than cryptographic ones, as the time lock prevents withdrawal until a specified time has passed. However, it's worth noting that while the time lock protects the funds, the account itself can still carry quantum risks. In comparison, the quantum threat to Bitcoin appears more significant due to its scale and structural issues.

A substantial portion of early Bitcoin was mined using a format that directly exposed public keys, including Satoshi Nakamoto's 1 million BTC, which has never moved. Google estimates that about 6.9 million BTC are vulnerable, equating to nearly 35% of Bitcoin's circulating supply. Bitcoin holders face a structural problem in protecting their funds, as the blockchain lacks a key rotation feature, forcing holders to move funds to a new address, which temporarily exposes the old address's public key to potential quantum attacks.

Although this risk is still theoretical, it underscores the relative vulnerability of Bitcoin holders. It's notable that Bitcoin developers have initiated proposals to develop quantum resistance.