Off the Block: Can quantum computers break Bitcoin? Experts weigh in

A sufficiently powerful quantum computer could break the cryptographic keys that secure crypto wallets. That is not a fringe concern. It is the honest starting point for a serious conversation about what the quantum threat actually means in practice, and how far away it is.

In the 19th episode of Off the Block, 21shares Global Head of Research Eliézer Ndinga and Senior Researcher Karim AbdelMawla convened experts from Project Eleven, Castle Island Ventures, Coinbase, Anza/Solana, and the Ethereum Foundation to work through the question properly.

Understanding the quantum threat to digital assets

The episode was designed as a companion to 21shares' research paper Quantum computers can't break Bitcoin yet, which assessed the current state of quantum hardware against the specific cryptographic standards that Bitcoin and Ethereum rely on. The “yet” in that title carries real weight: the threat is directionally real, the timeline is genuinely uncertain, and different blockchains face different levels of exposure depending on how their cryptography is structured and how prepared their developer communities are to upgrade it.

For investors holding crypto through an exchange-traded product (ETP), the implications are distinct from those facing direct wallet holders. Those implications get direct treatment in the episode, alongside a debate about what should happen to the large quantity of bitcoin sitting in abandoned wallets, including coins mined in Bitcoin's earliest days, if quantum capability were ever to advance to the point where those wallets become vulnerable.

Current capabilities and cryptographic exposure

No. Current quantum computers cannot break the cryptographic standards that secure Bitcoin. The cryptographic method Bitcoin relies on, elliptic curve cryptography (ECC), would require a quantum computer far more powerful than anything that exists today. Estimates on when that threshold could be reached vary widely among researchers, and the Bitcoin network has the ability to upgrade its cryptographic standards before that point, though doing so requires broad coordination across the network's developers, miners, and users.

No. Bitcoin addresses that have previously been used to send transactions expose their public key onchain, which creates greater theoretical vulnerability than addresses that have only received funds. Older address formats carry more exposure than modern ones. This means the risk profile for a long-dormant wallet using an older format is different from that of an address created recently using current standards. The episode covers Bitcoin's specific exposure at the 05:28 mark.

Custody implications and network governance

ETP investors do not hold private keys directly. Custody is handled by the product's appointed custodian, which means the relevant variables are the custodian's key management practices and their readiness to migrate to quantum-resistant cryptography when standards advance. ETP investors should review the custody arrangements disclosed in their product's documentation. The episode addresses this directly at the 24:28 mark. Past performance is not a reliable indicator of future results, and holding assets through an ETP does not eliminate all risk.

A significant quantity of bitcoin, including coins mined during Bitcoin's earliest years, sits in wallets that have not been accessed in many years. If quantum computing capability were to advance to the point where older wallet formats became vulnerable, it would raise a governance question: whether the Bitcoin network should take steps to protect or quarantine those coins before they could be exploited. This debate has no settled answer. Any resolution would require a network-wide governance decision, and the episode discusses the competing views at the 28:22 mark.