Post-Quantum Bitcoin Cash: Interview on Quantumroot

Thanks to Emmanuel Musa and Bitcoin.com News for this article:

Quantumroot Debuts on Bitcoin Cash: First Post-Quantum Vault on Bitcoin Script

Developer Jason Dreyzehner has unveiled Quantumroot, the first fully implemented, integration-ready post-quantum vault system.

Bitcoin NewsEmmanuel Musa

The full interview:

You’ve been leading development on Bitcoin Cash’s quantum-ready contract implementation. Can you explain what “quantum readiness” means in practical terms and why it’s becoming an urgent topic for blockchain security?

"Quantum ready" means that Bitcoin Cash could continue operating as sound money, even if a powerful quantum computer comes online. Cryptocurrencies that aren't quantum ready would be vulnerable to mass theft by quantum computers, and many Proof-of-Stake networks could also have their consensus hijacked.

Concern about quantum readiness has grown over the past few years following a series of quantum computing breakthroughs. We still can't be certain that a Cryptographically-Relevant Quantum Computer (CRQC) is possible, but the risk has risen enough that many businesses and institutions are already migrating.

For strongly decentralized systems like Bitcoin Cash, we can't just patch centralized servers: millions of holders need time to upgrade their wallet software and migrate to post-quantum addresses, a process which could take years. Meanwhile, cryptocurrencies are likely among the very first targets of CRQCs. By the time we're certain about the threat, it may be too late – only quantum‑ready cryptocurrencies will be able to transition smoothly.

2. How does your quantum-resistant design differ from the cryptographic protections currently used in Bitcoin and other major blockchains, and what specific threats does it aim to mitigate?

Quantumroot is uniquely ready for global scale. Bitcoin Cash's highly parallel architecture – the "UTXO model" – offers lower-level control than account-based systems, allowing Quantumroot to offer 100-1000x lower fees than equivalent vaults on Ethereum (and layer 2s reintroduce quantum-vulnerable signatures). Quantumroot uses a hybrid strategy for maximum efficiency and privacy: UTXO-based pre-quantum spending, with a hidden path for account-based, post-quantum recovery.

Quantumroot even outperforms today's most common BCH/BTC single-signature wallets ("P2PKH" or "P2WPKH") in important use cases. For example, for users who regularly buy or earn Bitcoin Cash (dollar-cost averaging), Quantumroot can save more than 10% on sweep transaction fees.

As for threats mitigated: Quantumroot is a highest-level, NIST Category 5 post-quantum vault, expected to remain secure for decades into the post-quantum era. It implements the standard LM-OTS signature scheme (RFC 8554), which itself relies only on SHA256 for security – no lattice-based or other relatively-experimental cryptography. From a cryptographic-security perspective, Quantumroot is maximally conservative.

Lastly, Quantumroot is highly-composable with other CashVM contracts: it enables post-quantum multi-signature vaults (30+ signers), threshold and fallback conditions, time-delayed withdrawals, percentage or amount-based pre-authorizations, inheritance and business-continuity configurations, destination-based withdrawal rules, and more.

3. What makes Bitcoin Cash particularly well-positioned to adopt quantum-secure features sooner than other networks, and what upgrades or consensus changes, would be required for full integration?

Post-quantum vaults have been possible on Bitcoin Cash since 2023, but Quantumroot uses features of the May 2026 Upgrade (activated November 15 on the Chipnet preview network) to make them highly efficient. All remaining work is at the wallet integration level – no further consensus changes are required.

Similar to the Ethereum Virtual Machine (EVM), Bitcoin Cash's restored Bitcoin Script (now called CashVM) enables wallet developers to implement new protocols without a network consensus upgrade. However, CashVM is uniquely powerful: transaction-level parallelization makes CashVM 100-1000x more efficient to validate than EVM and other account-centric VMs.

Fully-validating, archival BCH nodes run on consumer hardware and still outperform clusters of high-powered, centralized sequencers required by account-based networks. That translates to higher capacity, 100-1000x lower fees, and strong censorship-resistance – exactly what's needed to migrate millions of users to post-quantum vaults and applications.

4. Some argue that quantum threats are still decades away, while others believe the timeline is much shorter. From your vantage point, how real and how near-term is the risk to existing blockchain signatures and user funds?

Cryptographically-Relevant Quantum Computers (CRQCs) might never arrive – or they could arrive before 2030. Whatever the timeline, the asymmetry of the risk demands urgency: networks caught unprepared are unlikely to survive.

For more than a decade, the orthodox Bitcoiner response to the quantum threat has been, "If quantum computers ever work, Bitcoin will be the least of our concerns!"

This dismissive attitude helped to justify the Taproot upgrade, which worsened BTC's quantum vulnerability by deliberately omitting non-confiscatory upgrade paths for Taproot addresses as recently as 2021.

Governments, power grids, hospitals, aviation, fiat banking, the wider internet – much of the world is deploying or already running quantum-ready infrastructure.

Meanwhile Bitcoin, Ethereum, and other cryptocurrencies have millions of users to migrate, 0% migrated, and no practical migration paths available.

Fortunately, Bitcoin Cash wallets can already begin integrating practical, post-quantum vaults for May deployment. Better yet, Bitcoin Cash's quantum readiness doesn't come at the cost of network throughput, transaction fees, or user experience. Quantumroot offers immediate efficiency, privacy, and user experience advantages – even if Q-Day were still decades away.

5. If Bitcoin Cash successfully implements quantum-secure signing, how could this reshape its role in the global digital economy? Could quantum safety become a competitive advantage against other cryptocurrencies?

Quantum readiness makes Bitcoin Cash more reliable, both as sound money and as a peer-to-peer cash system. Yes, that's a competitive advantage, especially among top cryptocurrencies. It reinforces BCH's position as a multi-decade reserve asset, ready to safely store and transmit value in the post-quantum era.

Beyond quantum security, Quantumroot also highlights the competitive advantage of Bitcoin Cash's transaction-level parallelism: CashVM has matured into the most powerful programming environment for sound money – combining low fees, high throughput, and home-node decentralization.

Discussion on x.com: