The recent surge in interest in quantum computing, fueled by Google's claims that a powerful enough machine could breach legacy blockchains with relative ease, has sparked concerns among cryptocurrency holders. For XRP holders, experts offer a nuanced assessment: the architecture of XRP may be better equipped to withstand quantum threats than that of Bitcoin. XRP operates on the XRP Ledger, an open-source, decentralized blockchain utilized by Ripple for cross-border transactions. Let's delve into the details.

The quantum threat that has been making headlines is the potential for a powerful machine to reverse-engineer private keys from exposed public keys, thereby draining funds. Typically, public keys are exposed when sending transactions, while receiving funds only exposes the wallet address.

This means that account activity, rather than balance or address longevity, is what makes users vulnerable to quantum attacks. A recent audit of the XRP Ledger found that approximately 300,000 accounts, holding 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 accounts for only 0.03% of the circulating supply. It's worth noting that this vulnerability assumes these accounts are inactive and unable to utilize the 'key rotation' feature, which allows users to swap their signing key without moving funds. This feature, available to all users, enables them to change their account 'lock' without moving house, keeping their funds safe.

Mayukha Vadari, a staff software engineer at Ripple, highlighted the 'escrow feature' as an additional defense against quantum risk. Funds locked in escrow with a time lock are protected not by cryptography, but by logic, as the time lock prevents withdrawal until a specified time has passed.

While the time lock safeguards the funds, the account that locked them can still carry quantum risks. In comparison, the quantum threat to Bitcoin appears more severe.

A significant portion of early Bitcoin was mined using a format that exposed public keys directly, including Satoshi Nakamoto's 1 million BTC, which has never moved. Google estimates that around 6.9 million BTC are vulnerable, accounting for nearly 35% of Bitcoin's circulating supply. These coins are essentially 'sitting ducks' for potential quantum attackers.

Furthermore, Bitcoin holders face a structural problem: the lack of a key rotation feature, leaving them with only one option - moving funds to a new address. However, this process exposes the public key of the old address, making it vulnerable to quantum attacks. Although this risk is still largely theoretical, it highlights the relative structural vulnerability of Bitcoin holders. It's worth noting that Bitcoin developers have already initiated proposals to develop quantum resistance.