The Quantum Threat to Blockchain: Who’s Ready? with Alex Pruden

Table of Contents

Alex Pruden Introduction + Project 11

Alex Pruden’s path to the intersection of quantum computing and blockchain was anything but linear. After graduating from West Point in 2008, he spent nine years in the U.S. Army, including time as a Green Beret deployed to the Middle East. It was during that deployment in 2015 that he first encountered Bitcoin. His team was training Syrian rebel forces across the border from Turkey, and they briefly explored using Bitcoin as a way to compensate those fighters, people who needed to buy goods on the local economy and didn’t want to use cash. The idea never went anywhere operationally, but the concept of borderless money captivated him.

When he returned home and decided to leave the military, he enrolled at Stanford Graduate School of Business. While there, he started the Stanford Blockchain Club and began moonlighting in computer science cryptography classes. A professor took pity on him and made introductions that set his career in motion, first to Coinbase, where he interned as the company was scaling, and then to Andreessen Horowitz’s crypto team, where he became an investment partner on their first fund. That era covered major protocols like Solana and Avalanche, as well as Facebook’s ill-fated Libra project.

But Pruden discovered he preferred operating over investing. He left a16z to join Aleo, a project building privacy-preserving smart contracts, essentially a Zcash-style approach to Ethereum. As the first employee of a four-person technical team, he eventually became CEO and led the protocol from zero to launch over four years. After stepping down in 2024, he found himself reflecting on what had inspired each career pivot: just as his military experience drew him into crypto, his experience at Aleo pushed him toward post-quantum cryptography.

The catalyst was Google’s Willow paper in 2024, which described new progress in quantum computing. Pruden began wondering how difficult it would be for the crypto industry to migrate all of its cryptography to post-quantum alternatives. Having just lived through the grueling process of launching a layer-one blockchain, with its delays, its billions of dollars in secured value, and the understanding that you only get one shot at launch, he realized this transition would be a monumental effort for the entire industry. That realization led him to found Project 11, a company focused on future-proofing digital assets against the quantum threat.

Playing the Long Game: The Quantum Threat

For anyone who has publicly discussed the quantum threat to blockchain, the experience often comes with hostility. Pruden has felt it firsthand. After the Google paper was released, which cited Project 11 for helping the quantum research community understand that blockchains use a different cryptographic system than RSA, he went on a press tour that put him on a soapbox to discuss risks that many in the crypto space didn’t want to hear about. He was attacked personally and professionally.

What surprised him most was how controversial the topic remains within the field of cryptography itself. He knows respected cryptographers who believe quantum computing will never happen. On the other end of the spectrum, quantum physicists, including advisors to Project 11, such as the CEO of QuEra (a neutral-atom quantum computing company that recently raised $1.3 billion), are convinced the breakthrough is imminent. The divergence between the quantum computing research community and the cryptography community has been striking, though it has finally begun to narrow.

Part of the friction comes from the intersection of multiple complex technologies. Blockchain is still inherently complex for most people, even at the level of basic self-custody. Quantum computing is equally complex. And the people who need to solve this problem, blockchain developers, quantum physicists, and cryptographers, have not all been in the same room yet. Each group brings a necessary skill set, and when blockchain developers speak authoritatively about the likelihood of quantum computing, it raises questions about whether they truly understand a field outside their expertise.

The tribal nature of blockchain compounds the problem. The hosts note that in 2017 and 2018, Bitcoin maximalism resembled a religion in its fanaticism. Over time, some who have been deeply involved in the space, including one of the hosts, who has been in Bitcoin since 2013, have developed genuine doubts about Bitcoin’s future, not just because of the quantum threat but also because of consensus disparities and misaligned incentives that are hard to quantify but impossible to ignore.

Pruden frames the issue around trust. People invest in Bitcoin because they trust the cryptography will never be broken. They trust the network. If you try to compromise even some of that trust, $1.5 trillion in Bitcoin value becomes a very large question mark. Even without a definitive answer on when a quantum computer arrives, being proactive about this existential risk strengthens the trust these systems depend on. It seems reckless, in his view, to feel no need to plan and prepare.

The hosts add a practical dimension: it no longer matters whether individuals personally believe in quantum computing. Governments have already been working on post-quantum standards, mandating that their own systems be upgraded by 2029 or 2030 in countries including the United States, China, and Australia. Corporate systems will follow government standards, and retail and open-source projects will follow suit. At some point, post-quantum security will simply be assumed, just as cryptography evolved from pen and paper to mechanical devices to integrated circuits to software, post-quantum will eventually become the new classical standard.

What People Say Privately That They Won’t Say on a Panel

When Project 11 started about two years ago, the first reaction from the industry was outright denial, quantum computing doesn’t exist, and the very notion was laughable. Pruden says he and his team were literally laughed at at conferences. That phase has passed. The industry has accepted that quantum is real. But the new consensus has shifted to a different kind of dismissal: “If quantum is real, we can just solve it. No problem.”

This, Pruden argues, is the next barrier of ignorance. The problem has less to do with quantum computing itself and more to do with security engineering and how blockchain systems are built. Virtually every chain depends on classical cryptography, specifically elliptic curve cryptography. Aleo, for instance, uses a zero-knowledge proof system that relies on the discrete log assumption for soundness. In a post-quantum world, that proof system breaks. While you can argue about whether a specific protocol would actually be targeted, the underlying cryptographic guarantee is fundamentally broken, and that’s true universally across the space, with rare exceptions like QRL, which was built from the ground up with post-quantum security in mind.

The deeper issue is that once teams accept the problem, they then have to accept what it will take to fix it. Different teams are at different points along that spectrum. Decentralized architectures are a blessing and a curse: they enable trustless systems, but they make cryptographic migration nightmarish because of the countless dependencies scattered throughout the stack.

Consider custody. Many networks today rely on threshold cryptography, a sophisticated version of multisig, which is entirely dependent on elliptic curve cryptography. Move away from elliptic curve cryptography, and the ability to shard or share keys among multiple parties and combine them into a single signature disappears. That mechanism is the foundation of the entire digital asset custody industry. And beyond that, there’s the question of which post-quantum algorithm to adopt, since blockchains have unique performance and size constraints that make this far from a flip-the-switch scenario.

The hosts draw a sharp contrast to Y2K. With Y2K, everyone knew exactly what would happen and when. There was a hard deadline. The fix was centralized, IT departments working together. With quantum, there’s no known date. The entities with the most powerful quantum machines have every incentive to keep that capability secret. And the solution, in a decentralized blockchain world, requires the entire global community to coordinate across competing interests.

Under-Discussed Aspects of Migrating a Blockchain to Post-Quantum

One of the most under-discussed aspects of post-quantum migration is the cost, and we’re not talking about engineering hours. When a blockchain eventually has to disable legacy signature schemes, it faces a fundamental dilemma: do you freeze assets that haven’t been migrated, or do you leave them vulnerable to a quantum attacker?

This touches on the core philosophy of blockchain. The entire ethos was built on the principle of “your keys, your crypto.” Quantum computing has the potential to break that compact, you can still hold your private keys and suddenly no longer hold your crypto. There are also fungibility questions: if a token exists on a classical chain and a quantum-secure chain under the same ticker, are they really the same asset?

The hosts argue that upgrading a blockchain to post-quantum security has the potential to completely rewrite what blockchain means by eroding its trust model and foundational philosophy. It’s a theory they don’t hear discussed much in public crypto discourse.

Pruden illustrates the challenge with a concrete example beyond Bitcoin. Take Circle and USDC. Circle is a centralized company that could upgrade its smart contracts to be post-quantum secure relatively easily. But the USDC that has been issued sits under keys that Circle doesn’t control. Just as Bitcoin can’t upgrade Satoshi’s coins, Circle can’t upgrade a user’s USDC. Now imagine a payment system built on USDC, how is it supposed to distinguish between a legitimate owner and a quantum attacker? Ownership on blockchains, in a world with a cryptographically relevant quantum computer and classical assumptions, ceases to have meaning.

The hosts summarize the problem by noting that every known migration scheme, hybrid chains, forking to new post-quantum signatures, time-delayed mechanisms, shares one thing in common: the user has to do something. There is no system-wide function built into Bitcoin or other chains that can force migration. And history has shown that a significant portion of users simply won’t act.

Alex on Zcash

Zcash offers a vivid illustration of the migration challenge. As a privacy-preserving version of Bitcoin using zero-knowledge proofs, Zcash recently shipped a new shielded pool with a post-quantum recoverability mechanism, a novel approach that could help seamlessly migrate users from a quantum-vulnerable system to a post-quantum secure one. Pruden applauds this work.

But Zcash also reveals exactly why migration is so hard. The network doesn’t have just one shielded pool. It has multiple pools, accumulated over successive upgrades. Orchard, the pool that’s now meant to be deprecated in favor of the newer Ironwood pool, still holds significant funds. The pool before Orchard, Sapling, still contains roughly 20% of all shielded Zcash. You can see this yourself on the Zcash block explorer.

Every time there’s an upgrade, some users move to the new pool. And every time, without fail, there are leftovers, people who lost their keys, don’t care, or never got the memo. In a quantum scenario, the community faces an impossible choice: effectively confiscate or freeze those leftover tokens, or let a quantum computer steal them. As one host puts it, it’s not really a debate about whether coins will be taken, it’s a question of who’s going to take them. And you could have a run on the bank, orders of magnitude worse, potentially before most people even realize what’s happening.

This isn’t purely a mathematical problem. It’s a socioeconomic one. Mathematics underpins the trust model, but the downstream impacts on real people holding real value are what make this so difficult, and too often, the researchers working on solutions are thinking about it in a purely academic way, without considering what it means for a deployed monetary system.

Blockchain Philosophy and More

At its core, the conversation about post-quantum migration is philosophical. Blockchain was founded on the principle that what’s mine is mine, cryptographic ownership conferred to the end user, with no central authority able to override it. That uniquely cryptographic guarantee of ownership is, in Pruden’s view, what makes blockchains special. Even if consensus rules are controlled by a small group, the ownership of the asset sitting with the end user is what distinguishes a blockchain from any other system.

This is fundamentally different from the migration challenge facing companies like Google. Google will upgrade all its systems by 2029 with a centralized team working toward shared goals. Blockchains require the entire decentralized community to reach consensus, across competing interests, philosophical camps, and technical disagreements.

The host raises a provocative point about precedent. If the Bitcoin community could reach consensus to confiscate Satoshi’s coins, an idea CZ recently floated, it would open a door. If you can justify confiscating from the inventor of Bitcoin in the interest of protocol security, it sets a precedent for confiscating from smaller holders. It rewrites the narrative of what blockchain means.

Pruden, whose undergraduate degree is in political science, notes that blockchains are political systems as much as anything else. Questions of majority rule versus minority rights, rule of the masses versus rule of elites, come up implicitly all the time. Different ecosystems will decide for themselves where they fall on that spectrum. But there is one bright line: if one person can press a button and make everyone post-quantum secure, it’s definitively not a blockchain.

What Part of the Quantum Threat Is Still Being Underestimated?

The part that’s most underestimated isn’t the timeline of quantum computing itself, it’s the gap between talk and action. It’s far easier to write a paper about an idea than to engineer and ship it. Pruden would rather see more resources directed toward the solutions we have at hand right now, because even taking what’s currently available, it’s going to take everything the industry has just to get there in time.

A post-quantum secure transaction does not make a post-quantum secure blockchain. The full migration, from design to implementation, testing, auditing, deploying new signature schemes, sandboxing, and finally getting every user to migrate their keys, is an enormous, multi-year undertaking. And when you see announcements that a chain is “post-quantum ready,” it’s worth asking whether the people making those claims understand the difference between enabling a post-quantum transaction and completing a full migration where all legacy schemes are disabled, winners and losers have been determined, and some coins have inevitably been lost or invalidated.

Mosca’s Inequality Theorem

To frame the urgency, Pruden applies Mosca’s Inequality, a framework developed by Michele Mosca, a researcher at the University of Waterloo. The concept is straightforward: there are two timelines. One is how long until a cryptographically relevant quantum computer arrives. The other is how long it will take you to be ready. If the second bar extends past the first, you have a problem.

Most of the conversation up to this point has been arguing that people underestimate the second bar, the time it will take to get ready. But what about the first? Project 11 released a report estimating that there’s a better-than-even chance Q-Day, the arrival of a cryptographically relevant quantum computer, occurs by 2032, with as much as a 10% chance by the end of 2030, within roughly four and a half years.

Those numbers come from three sources. First, an annual global risk survey that polls cryptographers and quantum researchers on how far away they think the threat is. In the last year, expert consensus has pulled forward dramatically, shifting from 15–20 years to “almost certainly within 10.” Second, the public roadmaps of quantum computing companies, IBM, Google, IQM, QuEra, which, while they don’t usually discuss cryptographic applications directly, all point toward cryptographic relevance by the end of the decade when you read between the lines. Third, napkin math on the key bottlenecks: logical qubit counts, qubit lifetimes, the requirements of Shor’s algorithm, laser technology, and more, with a fixed annual rate of improvement applied to each.

This is where Project 11 gets its name. In Mosca’s Inequality terms, it’s already the eleventh hour. And the evidence bears that out. BIP360, the Bitcoin improvement proposal for post-quantum security, received a BIP number about a year ago. In the year since, it has essentially not moved. The proposal is at the same point it was twelve months ago. The host adds that after years of research, he has been unable to find a clean way to migrate Bitcoin to post-quantum security. Bitcoin developers are extremely creative, the time-delay transaction idea, for instance, was something he wouldn’t have thought of, but it still doesn’t fully solve the problem. At the end of the day, something important will have to be sacrificed.

There Will Be Forks, Expect Chaos

When Bitcoin forks, and the hosts believe it will, the fallout will extend far beyond the crypto community. Bitcoin is now integrated into traditional finance through ETFs, which one host describes as “papering over” Bitcoin the way gold has been papered over. When the Bitcoin community initially celebrated the ETF approval as a long-awaited recognition, this host saw it as cause for concern.

Now imagine Bitcoin forking into multiple competing chains when the quantum migration forces philosophical schisms. The host envisions idealists forming one camp, private corporate interests forming another, and possibly two or three or four factions, like the block wars, but with more prongs and higher stakes. What happens to the price of Bitcoin when it splinters? What does TradFi do when the underlying asset fractures? His distillation, built over years of study, is simple: there will be forks. Expect chaos.

Pessimistic and Optimistic Takes

Pruden offers both a pessimistic and an optimistic view.

On the pessimistic side, there are chains and ecosystems, even quite large ones, that simply will not survive the transition to a post-quantum world. They will collapse under the weight of philosophical contradictions and the sheer challenge of executing the migration. Their value will fall to zero. This could possibly be the majority of existing chains and value currently in the space.

On the optimistic side, there is no reason this problem can’t be solved. People have been building toward this for years. QRL is an example of a protocol built from the ground up for post-quantum security. Existing chains are also taking the threat seriously and working on solutions. Blockchains are built on trust, which is messy, but that messiness also embeds resilience. The real question is how much chaos the community wants to endure before reaching the other side. That choice is up to us. We can prepare now by adopting post-quantum cryptography, or we can keep fighting over incremental improvements while the clock ticks.

Some version of Bitcoin and every digital asset will definitely survive the post-quantum transition. But it’s a question of which ones, which communities, and what they’re willing to do in response.

Learn More About Project 11

For those interested in going deeper, Project 11 has compiled an extensive report on quantum computing and blockchains, available at report.project11.com. The main website, project11.com, hosts additional content covering everything from wallet architecture to specific schemes proposed for Bitcoin migration, along with a newsletter for staying up to date.

Project 11’s primary focus is building infrastructure for institutional holders of digital assets who want to begin preparing for the post-quantum world. While protocols are where cryptography ultimately lives and where assets are issued, the infrastructure layer, what institutions actually use to interact with those assets, is where Project 11 concentrates its efforts. A new product launch in this vein was forthcoming at the time of this conversation.

The report also includes an extensive bibliography with roughly a hundred sources for anyone who wants to continue researching independently.

Conclusion

The conversation makes one thing clear: the quantum threat to blockchain is not a distant theoretical concern. It is an approaching reality with a timeline measured in years, not decades, and the migration it demands will be the most complex coordination problem the crypto industry has ever faced. It will require not just new cryptography but new consensus, new infrastructure, and new answers to old philosophical questions about what ownership means on a blockchain. The industry can choose to prepare now, or it can choose to endure the chaos of an unprepared transition. Either way, the transition is coming.