- It’s a race against time for Bitcoin and Ethereum as the countdown to the arrival of quantum computers that could break their cryptographic design has begun.
- The “Great Migration” is underway, as a protocol that can’t migrate to post-quantum cryptography is one with an expiration date.
Imagine waking up tomorrow only to find that the seemingly unbreakable cryptographic models of Bitcoin (BTC) and Ethereum (ETH) have been solved. Over the years, the “quantum threat,” or “Q-Day,” has been the boogeyman in crypto campfire stories.
Many initially dismissed it as Y2K-level mumbo jumbo that would never happen. Fast-forward to 2026, and it’s all becoming all too real.
“Harvest Now, Decrypt Later”
While the technology that will inevitably break the shield of Bitcoin and altcoins is still under rigorous development, cybersecurity experts warn that we are now in the stage of “Harvest Now, Decrypt Later.” The people at Palo Alto explain it as the process by which state actors and hackers are already capturing encrypted data today, so they can untangle it once quantum computing reaches that capability.
Accounts with exposed public keys, which are common in reused Bitcoin addresses or active Ethereum EOA (externally owned accounts), are vulnerable to a targeted quantum attack.
This scenario means bad actors are clearly making their move now, and the doomsday clock for crypto is near midnight. Cracking the cryptographic code is no longer a matter of “if,” but a matter of “when.”
Shor’s Algorithm: A Looming Threat
Most cryptocurrencies, including Bitcoin and Ethereum, use the Elliptic Curve Digital Signature Algorithm (ECDSA). The mathematical tool serves as a “one-way door,” keeping keys private while generating digital signatures to authenticate transactions and verify the sender’s identity.
Quantum computers do not merely work to “guess” the keys faster. They employ quantum physics, notably Shor’s algorithm, to overcome the mathematical barriers, such as the discrete logarithm problem (DLP) and integer factorization, that underpin crypto’s encryption models, which modern computers struggle to solve.
New Scientist said a quantum computer with 13 million qubits could accomplish such a feat in a whole day, while one with 317 million qubits could do that in an hour. Meanwhile, Coinbase Global Head of Investment and Research David Duong estimates that around 6.51 million BTC, or roughly 32.7% of Bitcoin’s supply, are in address types vulnerable to long-range quantum threats.
Among the vulnerable addresses are those using P2PK (Pay-to-Public-Key), a simple Bitcoin script that locks funds to a recipient’s public key directly and is already visible on-chain. Then there are the reused P2PKH (Pay-to-Public-Key-Hash) addresses, which utilize Bitcoin’s legacy script format. Next is Bitcoin inventor Satoshi Nakamoto’s 1.096 million BTC holdings, which are also stored in the blockchain’s early formats and couldn’t be moved without exposing them to the same quantum-level threat.
Lattice-Based Cryptography
Expert consensus points to Lattice-based cryptography as a solution to the looming quantum threat. Cloudflare considers it the first paradigm that will replace ECDSA,
Lattices are much harder to crack because they use high-dimensional grids of points to obscure information. Due to Lattice-based cryptography’s reliance on much more complex mathematical problems that are incredibly hard to solve, it’s the prime candidate for migration to post-quantum (PQ) security.
Simply put, Lattice-based math is like finding a needle in a massive 500-dimensional haystack, even for quantum computers. These are now being baked into new standards like Falcon and ML-DSA (Module-Lattice-Based Digital Signature Algorithm, and formerly Dilithium) at the core of the Internet, and blockchains are next for their transition to a post-quantum future.
Bitcoin and Ethereum’s PQ Approaches
The PQ approaches to the decentralized networks of Bitcoin and Ethereum differ. So far, the latter is already moving quickly, with its founder, Vitalik Buterin, amplifying the call to implement measures to get the chain ready for Q-Day.
Ethereum’s Account Abstraction (AA) allows one to basically “plug in” a new quantum-proof lock to an existing wallet without needing a new address. It enables smart contracts to implement quantum-resistant cryptography, such as PQ-signatures, without modifying the core protocol.
Moreover, the PQ solution for Ethereum decouples account logic from signatures, making the former more flexible and better prepared for upgrades, thereby introducing an additional layer of protection and improving the user experience while paving the way for quantum-safe transactions.
In Bitcoin’s case, Research from the Journal of British Blockchain Association suggests a “defensive downgrade.” Security could be improved for quantum readiness, but it could reduce block capacity by half. This is primarily due to the chain’s “ossified” structure, which makes it harder to implement radical changes without risking a network split or the so-called “hard fork” in crypto lingo.
Unlike Ethereum’s flexible nature, Bitcoin’s security is embedded directly into its foundation. Since lattices require much more communication than elliptic curves, a shift to PQ signatures, which are significantly larger in data size, would take up more space in each block.
The trade-off is that Bitcoin migrates to a quantum-safe state, but transaction fees could rise and the network could slow down dramatically. This “security tax” is the subject of a heated debate in the crypto community.
The British Blockchain Association estimates that a permissionless network like Bitcoin would incur a 60%-70% performance hit and increase permanent storage by 59x. As a result, its PQ cryptography (PQC) migration could lead to a twofold to threefold increase in transaction fees.
Playing It Safe With a Hybrid Approach
Most wallets this year are adopting a more measured approach to PQ migration to avoid breaking anything during the transition. Instead of a “hard switch,” they’re integrating hybrid architectures that use the legacy math for compatibility and the new algorithm.
We are also seeing the emergence of “Bitcoin Yellowpages,” like the one from Project Eleven. These are registries where users can link their old Bitcoin addresses to new quantum-safe keys, supposedly getting them ahead of the curve.
Final Thoughts
The quantum threat is not the end of crypto; it’s the beginning of a new era for its ecosystem. The “Great Migration” is already happening.
Is your wallet ready for the post-quantum future?
